Essentials of General, Organic, and Biochemistry by Macmillan International Higher Education

The essential chemistry for health careers and everyday life.

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The essential chemistry for health careers and everyday life. Guinnâ&#x20AC;&#x2122;s Essentials of General, Organic, and Biochemistry uses health and medicine as the framework for learning the fundamentals of chemistry. The newly-revised third edition focuses on core concepts and necessary math skills with a newly revamped organization. Easily-digestible content is served in shorter, concise chapters, while medical applications make chemistry meaningful for students preparing for future careers in nursing and other allied health professions. Paired with SaplingPlus and an embedded e-book, students will be able to focus their study with adaptive quizzing and understand the relevance of chemistry through videos, animations, and case studies. Integrates Health and Medicine Chemistry is the central science, yet students often struggle to see its connection to their lives and career goals. Examples from medical and allied health fields and other consumer-based examples illustrate the fundamental concepts of chemistry throughout the entire GOB sequence of topics. Content is tailored to motivate students and help them understand how chemistry applies to their lives and majors. Supports Student Success The third edition of Essentials of General, Organic, and Biochemistry ensures students successfully learn chemistry by reinforcing core concepts, math skills, and problem-solving techniques. Bolstering studentsâ&#x20AC;&#x2122; abilities in these areas builds confidence and provides the necessary foundation they need throughout the course. Promotes Independent Practice with SaplingPlus Guinnâ&#x20AC;&#x2122;s third edition of Essentials of General, Organic, and Biochemistry is now paired with SaplingPlus, promoting student study and practice. Adaptive LearningCurve assignments help direct purposeful reading and study, while tutorials and case studies help students synthesize and apply their understanding. In addition, students and instructors will have access to the acclaimed Sapling Learning online homework and access to industry-leading peer-to-peer support for help with implementation and technical support.

New Edition! Essentials of General, Organic, and Biochemistry, Third Edition Denise Guinn, The College of New Rochelle Publishing December 2018 (ÂŠ2019) ISBN: 978-1-319-07944-4 Loose-Leaf Version ISBN: 978-1-319-19286-0 SaplingPlus (Twelve-Month Access) ISBN: 978-1-319-25238-0

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D EN IS E G U IN N received her B.A. in chemistry from the University of California at San Diego and her Ph.D. in organic chemistry from the University of Texas at Austin. She was a National Institutes of Health postdoctoral fellow at Harvard University before joining Abbott Laboratories as a Research Scientist in the Pharmaceutical Products Discovery Group. In 1992, Dr. Guinn joined the faculty at Regis University, in Denver, Colorado, as Clare Boothe Luce Professor of Chemistry, where she taught courses in general chemistry, organic chemistry, and the general, organic, and biochemistry course for nursing and allied health majors. In 2008, she joined the chemistry department at The College of New Rochelle in New York where she teaches organic chemistry, biochemistry, and the one-semester GOB course for nursing students. She has published in the Journal of Organic Chemistry, the Journal of the American Chemical Society, and the Journal of Medicinal Chemistry. She has two adult sons, Charles and Scott, who also assisted in the revision of the second and third editions. She currently resides in Nyack, New York with her dog, Puck, where she enjoys kayaking on the Hudson River in her spare time.

Integrates Health and Medicine Chemistry is the central science, yet students often struggle to see its connection to their lives and career goals. Examples from medical and allied health fields and other consumer-based instances illustrate the fundamental concepts of chemistry throughout the entire GOB sequence of topics. Content is tailored to motivate students and help them understand how chemistry applies to their lives and majors.

Concepts in Context: Each chapter opens with a short, practical, and real-life example of a health-related topic connected to the chapter concepts. These stories immediately immerse the student in a high-interest topic related to health and medicine.

Authentic Images: Photos related to clinical practice, as well as consumer and healthcare products, reinforce chemical concepts and show their applications.

Chemistry in Medicine: Guinn concludes each chapter with an in-depth look at how the chemical principles described in the chapter directly apply to health care issues.

Case Studies: Available as student handouts, case studies allow students to apply what they learn to more challenging problems, connect the chemistry they are learning about with medical topics, and provide instructors with tools for active learning. Students also have the opportunity to synthesize their understanding by working through paired case studies in SaplingPlus.

Supports Student Success The third edition of Essentials of General, Organic, and Biochemistry ensures students successfully learn chemistry by reinforcing core concepts, math skills, and problem-solving techniques. Bolstering studentsâ&#x20AC;&#x2122; abilities in these areas builds confidence and provides the necessary foundation they need throughout the course.

Core Concepts: These boxes in the margin emphasize important concepts within each chapter and provide a quick study tool for students reviewing chapter content.

Math Tips: These boxes in the margin refresh students on key mathematical techniques at relevant points in the text.

Guidelines: These boxes throughout the text provide step-by-step instructions for key chemistry operations (such as calculations or nomenclature).

Additional features to help students with problem solving and math skills: Worked Exercises: The author walks students through the steps for solving problems, pointing out important concepts and explaining each necessary step to solve a problem.

Practice Exercises: Additional Practice Exercises follow the Worked Exercises, allowing students to test their understanding of the material.

There is also a Math Appendix that provides students with a primer of necessary math skills.

Promotes Independent Practice with Guinnâ&#x20AC;&#x2122;s third edition of Essentials of General, Organic, and Biochemistry is now paired with SaplingPlus, promoting student study and practice. Adaptive LearningCurve assignments help direct purposeful reading and study, while tutorials and case studies help students synthesize and apply their understanding. In addition, students and instructors will have access to the acclaimed Sapling Learning online homework and access to industry-leading support for help with implementation and technical support.

SaplingPlus now includes a new VitalSource e-book. This e-book is also available through an app that allows students to read offline or have the book read aloud to them. Additionally, students can highlight, take notes, and search for key words.

LearningCurve is an adaptive quizzing system that promotes purposeful reading and study. These game-like formative assessments are available for every chapter of the text.

Tutorial Questions take students through a multi-concept question by breaking it into individual stepped-out problems. These activities help students break down complex problems and guide them with hints and targeted feedback at each step, building their confidence and competence. Students can then apply these problem-solving skills when they tackle similar problems on their own. In addition, Case Studies give students the opportunity to build upon their knowledge and synthesize their understanding. These more challenging problems apply chemistry concepts to medical topics.

Anatomy of a Sapling Problem Sapling offers multiple question types that enhance student engagement and understanding. Each problem includes hints, answer-specific feedback, and detailed solutions, ensuring student learning and emphasizing the pedagogical value of homework.

Hints attached to every problem encourage critical thinking by providing suggestions for completing the problem, without giving away the answer.

Targeted Feedback is included for each question, specifically targeting each studentâ&#x20AC;&#x2122;s misconceptions.

Detailed Solutions reinforce concepts and provide an in-product study guide for every problem in the Sapling Learning system.

Table of Contents

1. Matter, Energy, and Measurement

For improved flexibility, discussion on compounds from the previous edition has been divided into two shorter chapters: Chapter 3 on “Ionic and Covalent Compounds,” and Chapter 4 on “Molecular Geometry, Polarity, and Intermediate Forces of Attraction.”

2. Atomic Structure and Radioisotopes 3. Ionic and Covalent Compounds 4. Molecular Geometry, Polarity, and Intermolecular Forces of Attraction 5. Chemical Quantities and Introduction to Reactions

For improved flexibility, discussion of chemical quantities and reactions from the previous edition has been divided into two shorter chapters: Chapter 5 on “Chemical Quantities and Introduction to Reactions” and Chapter 6 on “Chemical Reactions: Energy, Rates, and Equilibrium.” Additionally, a new section on the basic types of reactions has been added to Chapter 5.

6. Chemical Reactions: Energy, Rates, and Equilibrium 7. Changes of State and Gas Laws 8. Mixtures, Solution Concentrations, and Diffusion

Expanded discussion of heating and cooling curves. Specific heat discussion moved here from Chapter 1.

Discussion on eq/L has been replaced by discussion of ppm and ppb.

9. Acids and Bases, pH, and Buffers 10. Introduction to Organic Chemistry: Hydrocarbon Structure

Expanded discussion of acids and bases as electrolytes.

11. Alcohols, Phenols, Thiols, Ethers, and Amines 12. The Carbonyl Containing Functional Groups

Reorganized chapter. For example, discussion of branched hydrocarbons now follows discussion of aromatic rings.

13. The Common Organic Reactions in Biochemistry 14. Carbohydrates: Structure and Function 15. Lipids: Structure and Function 16. Proteins: Structure and Function 17. Nucleotides and Nucleic Acids 18. Energy and Metabolism

The discussion of stereoisomers moved to this chapter. An expanded discussion of Fischer and Haworth projections is included.

Section on protein architecture reorganized, to go from primary to tertiary structure to functional type.

A letter from the author

In teaching the general, organic, and biochemistry course for the past 26 years, it has been a great pleasure and opportunity to be part of the curriculum development of this course. In writing the first edition of Essentials of General, Organic, and Biochemistry, our goal was to make it obvious why chemistry is a cornerstone in the education of todayâ&#x20AC;&#x2122;s health care professionals by using health and medicine as the framework for learning the fundamentals of chemistry. The third edition contains additional medical applications, and the organization of material into smaller chapters. There seems to be a consensus that integrating medical applications throughout the text effectively engages students in the course early on, while at the same time making it feasible to learn the fundamental concepts of chemistry in a one-semester course. Based on feedback from hundreds of instructors, the chapters on solutions and acid base chemistry have been rewritten and appear before the chapters on organic chemistry. The third edition contains additional in-chapter worked exercises and practice exercises that help students learn problem solving and critical thinking skills. I hope that you feel, as I do, that the third edition has retained the elements of the previous editions that worked so well, while incorporating some organizational changes that better support student learning.

Science Photo Library/Alamy Stock Photo

Mixtures, Solution Concentrations, Osmosis, and Dialysis ConCepts in Context:

How the Kidneys Filter

Our blood Chronic Kidney Disease affects 14 percent of the united States population, and causes more deaths than breast cancer or prostate cancer according to the u.S. Department of Health and Human Services. When a personâ&#x20AC;&#x2122;s kidneys are destroyed by disease, a kidney transplant becomes the only option for the patientâ&#x20AC;&#x2122;s long-term survival. In the interim, the patient must undergo dialysis three or four times a week. Dialysis is a procedure that performs the function of the kidneys. Today, about half a million americans are on dialysis and 95,000 are actively awaiting a donor kidney according to unOS (united network for Organ Sharing). To understand how the kidneys filter our blood, we need to understand mixtures, the subject of this chapter. Mixtures are a type of matter composed of two or more elements or compounds. blood is a complex mixture that contains water, ions, elements, and molecules in addition to red blood cells, white

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Contents 8.1 Types of Mixtures 8.2 Solutions: Dissolving Covalent and Ionic Compounds in a Solvent 8.3 Solution Concentration 8.4 Solution Dosage Calculations in Medicine 8.5 Solution Dilution Calculations 8.6 Osmosis and Dialysis

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blood cells, and platelets. Maintaining the proper balance of these components of blood is essential, as our cells are constantly absorbing and releasing substances into the blood. In each kidney, blood enters through the renal artery and is then filtered by the one million nephrons in a kidney (Figure 8-1 insert). Our kidneys filter more than 200 liters of blood a day, removing cellular waste, toxins we may have ingested, and about two liters of surplus water, which exit the kidneys as urine through the ureters and are stored in the bladder until eliminated. This filtering process is performed by special membranes in the kidneys known as nephrons, which are selectively p ermeable membranes that allow some components of a mixture but not others to cross the membrane.

Figure 8-1 Blood enters the kidney through the renal artery, where it is filtered through the selectively permeable membranes in the nephrons. Waste and excess water exit the kidney through the ureter.

Kidney Nephron

Renal artery

Blood

Urine

Renal vein

Ureter

When the kidneys stop functioning, the body retains water and waste products, which causes swelling most noticeable in the hands and feet. When large molecules like proteins are detected in the urine, it is often a symptom of kidney damage, as normally proteins would not be removed by the kidneys but would be retained in the blood. Hemodialysis, or “dialysis” for short, is a life-support treatment that filters the blood and performs the function of the kidneys until a donor kidney can be located. Dialysis is described in the Chemistry in Medicine at the end of this chapter. ●

Core Concept: Mixtures are composed of two or more elements and/or compounds.

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n chapters 2–4 you learned about elements and compounds. In this chapter, you will learn about mixtures, a combination of two or more elements or compounds in any proportion. Mixtures are the most abundant type of matter. Air, gasoline, blood, and a cup of coffee are all examples of mixtures. This chapter begins with classifications of the different types of mixtures. We then focus on solutions, the most common type of mixture, and learn what it means at the molecular level for a compound to dissolve in a solvent. In section 8.3, we describe how to calculate the concentration of a compound or element in solution, the way scientists and medical professionals quantify how much of a particular compound or element is present in a mixture. We will learn that a blood test measures the concentration of important molecules, ions, and gases in the blood, which are used to assess

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8.1 • T ypeS OF MIX TureS

the health of a patient. At the end of the chapter, you will learn how to identify the components of a mixture that can cross a selectively permeable membrane, something your kidneys do routinely as they filter the blood and remove cellular waste products from the blood.

8.1

types of Mixtures

An important characteristic of a mixture is that it can be separated into each of its components (pure elements and compounds) through physical separation techniques. For example, we routinely separate out undesirable compounds in tap water using a carbon filter installed on the faucet (Figure 8-2a), or in a pitcher, such as the Brita shown in Figure 8-2b. Much more sophisticated techniques are available for separating mixtures in the laboratory and the clinic, and new separation techniques are continually being developed. Blood is a mixture containing many important components, including ions, molecules, and blood cells. In a blood test, a sample of blood is separated into its components and the quantity of some of the components is measured. Blood tests are used for a variety of purposes, including identifying illegal substances such as narcotics, steroids, and doping agents in the blood. This type of separation and analysis of a blood sample is routinely performed on athletes in major athletic competitions, such as the Olympics and professional sports.

Homogeneous and Heterogeneous Mixtures Mixtures are broadly classified as homogeneous or heterogeneous. The components of a homogeneous mixture are evenly distributed throughout the mixture, whereas the components of a heterogeneous mixture are unevenly distributed throughout the mixture. For example, a cup of coffee containing water, coffee flavors, caffeine, and sugar is a homogeneous mixture because these components are evenly distributed throughout the cup of coffee (Figure 8-3a). A piece of granite is a heterogeneous mixture because the components are not uniformly distributed throughout the mixture (Figure 8-3b). We see the various components of the rock are clumped together. There are two types of homogeneous mixtures: solutions and colloidal dispersions. These mixtures differ in the size of the minor component of the (a) Homogeneous mixture

Core ConCept: A mixture can be separated into its pure compounds and elements by physical separation techniques.

Core ConCept: The components of a homogeneous mixture are evenly distributed, whereas the components of a heterogeneous mixture are unevenly distributed throughout the mixture.

(a)

(b)

(a) Homogeneous mixture

(b) Heterogeneous mixture

Figure 8-3 (a) Coffee is a homogeneous mixture because its components are evenly distributed throughout the mixture. (b) Granite is a heterogeneous mixture because its components are unevenly distributed throughout the mixture. [(a) © D. Hurst/Alamy; (b) © sciencephotos/Alamy Stock Photo]

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Figure 8-2 Undesirable components of tap water can be removed by a commercial carbon filter, such as those installed on (a) a water faucet or (b) a Brita pitcher. [Layne Kennedy/Corbis Documentary/Getty Images; RomarioIen/Shutterstock]

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mixture, as described in the sections below. The most common type of heterogeneous mixture is a suspension, which contains undissolved solid particles in a liquid. Table 8-1 compares the characteristics of solutions, colloidal dispersions, and suspensions. Mixtures in which the major component is water are known as aqueous mixtures, abbreviated “aq” in a chemical equation. Blood is an aqueous mixture because the main component is water. table 8-1 Characteristics of a solution, a Colloidal dispersion, and a suspension Homogeneous Type of Mixture

Solution

Term for Major Component of Mixture

Solvent

Heterogeneous

Colloidal Dispersion

Suspension Medium

Colloid

particle

Size of Minor Component(s)

less than 1 nm

Minor Component

Small molecules and ions

1 nm – 1,000 nm 11 mm2

aggregates of molecules or ions; large molecules such as proteins (egg) and complex carbohydrates (starch)

greater than 1,000 nm 11 mm2

Physical Appearance of Mixture

Transparent

Opaque

Turbid and cloudy; individual particles visible

Examples of Mixture

Salt water, sugar water, alcoholic beverages, blood serum

Milk, mayonnaise, blood plasma, smoke, hand lotion

pepto-bismol, whole blood, sand in water

studiomode/Alamy Stock Photo

large insoluble particles, such as blood cells, sand, coffee grounds

Catherine Bausinger

Term for Minor Solute Component(s) of Mixture

Solutions Core ConCept: The main component of a solution is the solvent, and the minor components are the solutes: Solute(s) + Solvent = Solution.

Core ConCept: Solutions contain the smallest particles (,1 nm) dissolved uniformly throughout a solvent.

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The main component of a solution is known as the solvent, and the other one or more components are known as solutes. The solute and the solvent together are known as a solution. The solutes in a solution are less than 1 nm in diameter and dissolve in the solvent. Solutes include soluble monatomic ions, small polyatomic ions, small molecules, and elements. Solutions in which a solid solute is dissolved in a liquid solvent appear transparent although they may be colored, such as the blue aqueous solution of copper sulfate, CuSO4, shown in Figure 8-4. Solutions are not limited to solid solutes in liquid solvents. Table 8-2 shows some familiar solutions composed of solutes and solvents in all three states of matter at room temperature: solid, liquid, and gas. For example, dry

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air is a solution of nitrogen and oxygen where both the solute (oxygen) and the solvent (nitrogen) are gases. Nitrogen is the solvent because it is the major component of air. Mixtures composed of only gases are always solutions. Alcoholic beverages are aqueous solutions containing the solute ethanol 1C2H6O2, a liquid at room temperature. Dental amalgam is a solution composed of a solid solute, silver (Ag), in a liquid solvent, mercury (Hg). Metal alloys are solutions composed of a solid metal solute in a solid metal solvent. For example, bronze is an alloy of tin (solute) in copper (solvent).

table 8-2 solutions Composed of solutes and solvents in

Gas Solvent

Liquid Solvent

Solid Solvent

three states of Matter Solvent

Solute

Solution

Cu (s)

Sn (s)

bronze, a metal alloy

Hg (s)

ag (s) and Cu (s)

amalgam used in dentistry

ethanol (l)

I2 1s2

Tincture of iodine

H2O 1l2

ethanol (l)

alcoholic beverages unopened carbonated beverage

n2 1g2

CO2 1g2 O2 1g2

H2O 1l2

Figure 8-4 An aqueous solution of copper sulfate, formed by dissolving copper sulfate, CuSO4 1s2, the solute, in water (l), the solvent. [1989 Chip Clark/ Fundamental Photographs]

air

Colloidal Dispersions

The main component of a colloidal dispersion is called the medium, and the minor component(s) are known as colloids. Colloids range in size from 1 nm to 1 mm. Colloids include large molecules like proteins, starch, and fats, and small molecules or ions that are clumped together, known as aggregates, and evenly distributed throughout the medium. A colloidal dispersion is unique because the medium consists of particles that are much smaller than the colloids. Consider, for example, a colloidal dispersion of a protein in water: the water molecules are much smaller than the protein molecules, as illustrated in Figure 8-5. Because of the larger size of colloids, colloidal dispersions have an opaque appearance.

Core ConCept: A colloidal dispersion contains colloids, particles which are 1 nm to 1 mm in diameter.

Colloids

Figure 8-5 In a colloidal dispersion, the medium is composed of particles much smaller than the colloids.

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Examples of colloidal dispersions include milk, gelatin, and blood lasma, all of which contain proteins as the colloids. Colloidal dispersions p are also found in all three states of matter at room temperature. For example, hair gel and ointments are liquid colloids in a solid medium. Suspensions Core Concept: The particles of a suspension are larger than 1 mm. Suspensions are heterogeneous mixtures whose particles settle upon standing.

Whole blood

Blood plasma (55%)

Blood cells (45%)

Figure 8-6 Whole blood (left). Blood cells collect at the bottom of the test tube (right) after spinning at high speed in a centrifuge. The top layer is blood plasma, a colloidal dispersion.

Particles, the minor component of a suspension, are larger than 1 micrometer in diameter and can often be seen with the naked eye. In the absence of stirring, the particles of a suspension eventually settle due to gravity and their larger mass. The main component of a suspension is called the medium. The particles in a suspension are easily separated from the medium by filtration or with a centrifuge. A centrifuge is a standard piece of laboratory equipment that spins samples at high speed to separate the large particles from the medium in a suspension. Whole blood is a suspension. Blood cells are the particles in a suspension that can be removed from whole blood with a centrifuge. The mixture that remains is a colloidal dispersion known as blood plasma (Figure 8-6). Proteins and clotting factors are often removed from blood plasma, resulting in a solution known as blood serum, which contains ions, elements, and molecules dissolved in water. Some oral medications are formulated as suspensions because the active pharmaceutical ingredient is not soluble in any acceptable medium. Medications formulated as suspensions are often more suitable for children, who may have difficulty swallowing capsules. Suspensions must be shaken prior to use because the particles of active pharmaceutical ingredient settle upon standing.

Worked Exercises

Solutions, Colloidal Dispersions, and Suspensions

8-1 Classify the mixtures below as homogeneous or heterogeneous.

a. coffee grounds in water b. an alcoholic beverage c. sweat

Solution:

a. heterogeneous (a suspension), because coffee grounds are large visible particles in a medium of water, and they will eventually settle b. homogeneous, because the ethanol is evenly distributed throughout the aqueous mixture c. homogeneous, because sweat is a mixture of ions evenly distributed throughout an aqueous solution 8-2 Indicate whether the following examples represent a solution, a colloidal disper-

sion, or a suspension. Explain your reasoning. a. a glass of iced tea with a small amount of sugar b. clean dry air c. chalk dust in water d. hand lotion

Solution:

a. a solution, because sugar is a small molecule solute that dissolves in water forming a transparent solution b. a solution, because it is a mixture of nitrogen and oxygen gases. A mixture of only gases is always a solution

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8. 2 â&#x20AC;˘ Solutions: Dissolving Covalent and Ionic Compounds

259

c. a suspension, because chalk does not dissolve in water; instead the larger chalk particles will settle to the bottom and the smaller ones will float and both are visible to the naked eye d. a colloidal dispersion, because it is an opaque mixture with a uniform distribution of the colloids (medium-sized particles) in the medium 8-3 Identify the solute and the solvent in the solutions below. Refer to Table 8-2 if

necessary. a. an intravenous (IV) bag of 0.9% physiological saline (NaCl in water) b. a chlorinated pool, that is, a pool that has had calcium hypochlorite, Ca1OCl2 2, added to it c. a tincture of iodine

Solution:

a. solute: NaCl; solvent: water (it is present in the greater amount) b. solute: Ca1OCl2 2; solvent: water (it is present in the greatest amount) c. solute: iodine 1I2 2; solvent: ethanol (it is present in the greater amount) PRACTICE EXERCISES (You can find the answers to the Practice Exercises at the end of the chapter.)

2 3

Classify each mixture below as homogeneous or heterogeneous. a. a chocolate chip cookie b. calamine lotion c. an unopened bottle of a carbonated beverage d. the contents of an IV bag What is the difference in the size of the solutes in a solution, the colloids in a colloidal dispersion, and the particles in a suspension? Indicate whether the following mixtures are solutions, colloidal dispersions, or suspensions. a. 1 g of sugar dissolved in 35 mL of water b. Pepto-Bismol for the relief of an upset stomach, which must be shaken before use c. the contents of an unopened bottle of mineral water d. milk Identify the solute(s) and the solvent in each of the following solutions. a. a mixture of 5 mL of ethanol and 25 mL of water b. 200 g of water containing 6 g of NaCl and 2 g of sugar c. a gaseous mixture of 0.005 L of CO2 and 2 L of O2

8.2â&#x20AC;&#x192; Solutions: Dissolving Covalent and Ionic Compounds in a Solvent In this section, we focus on solutions and examine what occurs at the molecular level when different types of solutes dissolve in various solvents to form a solution. When a solute is added to a solvent, we observe the solute seeming to disappear; we say the solute has dissolved in the solvent. On the molecular level, individual solute particles become surrounded by solvent molecules, known as solvation or, when the solvent is water, hydration.

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Solvation of Covalent Compounds The solubility of a solute in a solvent depends on the polarity of the solute and the polarity of the solvent. Solutes dissolve in solvents with similar polarity, often expressed as “like dissolves like.” Thus, polar solutes dissolve in polar solvents, and nonpolar solutes dissolve in nonpolar solvents. Moreover, polar solutes do not dissolve in nonpolar solvents, and nonpolar solutes do not dissolve in polar solvents, as summarized in the diagram below.

Core Concept: “Like dissolves like” summarizes the observation that polar solutes dissolve in polar solvents and nonpolar solutes dissolve in nonpolar solvents.

Polar Solute

Nonpolar Solute

Polar Solvent

Soluble

Insoluble

Nonpolar Solvent

Insoluble

Soluble

Table 8-3 shows some common polar and nonpolar solvents. Hydrocarbons with five or six carbon atoms, such as pentane and hexane, are common nonpolar solvents because they are liquids at room temperature. Carbon dioxide in the liquid phase is used commerically as a nonpolar solvent. table 8-3 Common Polar and Nonpolar Solvents Polar Solvents Name

Nonpolar Solvents

Structure

Name

Carbon dioxide

Water H

Methanol

Hexane

H C

Structure

Ethanol H

2-Propanol

Pentane O

Diethyl ether

(isopropyl alcohol) H

Acetic acid H

H H

Nitrogen O

Ethylene glycol H

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Argon O

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8. 2 • SOluTIOnS: DISSOlvIng COvalenT anD IOnIC COMpOunDS

What happens at the molecular level when a covalent compound dissolves in a solvent? Intermolecular forces of attraction between solute molecules are broken and new intermolecular forces of attraction between the solute and the solvent are formed. No covalent bonds are broken during solvation. Solvation of polar Solutes in polar Solvents

When a polar solute containing hydrogen bonds is added to a polar solvent containing hydrogen bonds, the hydrogen bonds between solute molecules are replaced by hydrogen bonds between solute and solvent molecules. For example, when methanol is added to water, hydrogen bonds between methanol molecules are replaced with hydrogen bonds between methanol and water, forming a solution as shown in Figure 8-7.

Core ConCept: During solvation of a polar covalent compound, hydrogen bonds between polar solutes are broken and new ones are formed between the solute and solvent molecules. No covalent bonds are broken.

H O

Hydrogen bond

C H

Two methanol molecules hydrogen bonding

H C

H 1

Hydrogen bonds

H O

O H

Solvation

H Three water molecules hydrogen bonding

C H

H H H

One methanol and two water molecules hydrogen bonding

Figure 8-7 Hydrogen bonds between methanol molecules and some hydrogen bonds between water molecules are replaced by hydrogen bonds between methanol and water molecules.

Solvation of nonpolar Solutes in nonpolar Solvents

Nonpolar solute molecules interact with each other through dispersion forces. When a nonpolar solute dissolves in a nonpolar solvent, new dispersion forces of attraction are formed between solute molecules and solvent molecules. Dry-cleaning solvents are nonpolar solvents used to clean clothing by dissolving nonpolar components of dirt and stains with a nonpolar solvent rather than the polar solvent water; hence the reference “dry” cleaning. Immiscible liquids and the Hydrophobic effect

A nonpolar and a polar liquid are immiscible: two mutually insoluble liquids that form separate layers (Figure 8-8). Oil and vinegar is a familiar example of immiscible liquids. Oil is a nonpolar liquid and vinegar is a polar liquid. At the molecular level, water and a nonpolar liquid do not mix because that would require that water molecules sacrifice their hydrogen bonds to other water molecules to organize around the nonpolar molecules with which they cannot form hydrogen bonds (higher potential energy). Instead, the liquids form separate layers, known as the hydrophobic effect, which is driven by the natural tendency for solutions to attain their lowest potential energy. A nonpolar compound in water is said to be hydrophobic, from the Latin meaning “water fearing,” and polar compounds are hydrophilic, from the Latin meaning “water loving.”

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Figure 8-8 A nonpolar and a polar liquid form two immiscible layers. The less dense liquid is on the top. [Editorial Image/Science Source]

Core ConCept: The tendency for a polar and a nonpolar liquid to separate into two layers is a result of the hydrophobic effect.

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Supersaturated Solutions

There is a limit to how much solute will dissolve in a solvent at a particular temperature. For example, when sugar dissolves in water, hydrogen bonds between sugar molecules are replaced by hydrogen bonds between sugar molecules and water molecules. However, if we continue to add sugar, we eventually run out of water molecules to form hydrogen bonds with the sugar molecules. At this point, the solution is supersaturated and we observe sugar settling at the bottom of the glass (Figure 8-9 right). AÂ saturated solution contains the maximum amount of solute soluble inÂ solution at a given temperature (Figure 8-9 left). A supersaturated solution has more than the maximum amount of solute soluble in solution and exhibits properties of a suspension. Ionic compounds, discussed below, can also form supersaturated solutions. Kidney stones are caused by supersaturated solutions of calcium salts, such as calcium phosphate, Ca3 1PO4 2 2, and calcium oxalate, CaC2O4. When these calcium salts precipitate in the kidneys, they form kidney stones, which can be very painful when they pass through the urinary tract.

Core ConCept: A saturated solution contains the maximum amount of solute that can dissolve in a solvent at a given temperature. A supersaturated solution contains more than the maximum amount of solute and appears as a precipitate.

Figure 8-9 Left: a saturated solution showing the solute dissolved in the solvent. Right: a supersaturated solution showing some solute precipitated at the bottom of the glass. [Catherine Bausinger]

Worked exerCise types of solvents 8-4 Which of the following solvents are polar? Explain.

a. carbon dioxide, O

b. hexane, H

water, H2O

d. methanol, H H

solution:

The solvents c. and d. are polar because they have one or more polar O i H bonds, a bent geometry, and few C i C and C i H bonds. Therefore, they have hydrogen bonding intermolecular forces of attraction.

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8. 2 • Solutions: Dissolving Covalent and Ionic Compounds

WORKED EXERCISE Supersaturated Solutions 8-5 Student A adds 50 g of sodium nitrate, NaNO3, to 100 mL of water and observes

a clear colorless solution. Student B adds 100 g of sodium nitrate to 100 mL of water and observes a cloudy heterogeneous mixture. Which student has made a supersaturated solution? Why do these students observe different results even though they are both mixing the same solute and solvent?

Solution:

Student B has prepared a supersaturated solution. Student B has the same but twice as much solute as Student A, exceeding the amount that dissolves in 100 mL of water at that temperature, and therefore, resulting in a supersaturated solution.

PRACTICE EXERCISES

5 6 7 8

Explain the meaning of the saying “like dissolves like.” What “like” properties does this statement refer to? How is sugar “like” water? Based on the solubility characteristics of solutions, why do kidney stones form? On the macroscopic scale, how does a supersaturated solution look different from a saturated solution? Explain the difference on the molecular level. Explain why each of the following solutes would or would not be expected to dissolve in hexane. a. NaCl b. CCl4 c. CH3OH d. pentane 1C5H12 2 Urine, produced by the kidneys, is an aqueous solution containing urea and other small polar molecules and ions. Illustrate how a molecule of urea dissolves in water by showing one molecule of urea hydrogen bonding to three water molecules at three different places in the molecule. (Hint: Look for the polar bonds.) O H

C N

H Urea

Solvation of Ionic Compounds In chapter 3 we learned that ionic compounds are composed of cations and anions held together by strong ionic bonds: the forces of attraction between oppositely charged ions. Many, but not all, ionic compounds dissolve in water. At the molecular level, hydration of an ionic compound occurs when ionic bonds between cations and anions are broken and replaced by ion-dipole interactions. An ion-dipole interaction is the attraction between an ion and the opposite partial charges on several water molecules. Ionic compounds that dissolve in water do so because ion-dipole interactions are lower in potential energy than the ionic bonds of the crystalline solid in water.

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Core Concept: When an ionic compound dissolves in water, ionic bonds are broken and ion-dipole interactions are formed between each of the separated ions and the opposite partial charges on several water molecules.

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The ion-dipole interactions formed when sodium chloride, NaCl, dissolves in water are illustrated in Figure 8-10. The sodium cation, Na1 , forms ion-dipole interactions with the partial negative dipole (oxygen) on several water molecules, and the chloride anion, Cl2 , forms ion-dipole interactions with the partial positive dipole (hydrogen) on several water molecules.

d1 Cl–

H2O

Ionic bonds

d1 d1

Na+

Cl–

d1 d1

d2 Na+

d2 d2

Ion-dipole interaction

Figure 8-10 A molecular view of the hydration of sodium chloride. Ion-dipole interactions form between chloride anions 1Cl2 2 and the partial positive charges on several water molecules, and between sodium cations 1Na 1 2 and the partial negative charges on several water molecules.

Not all ionic compounds dissolve in water. Most ionic compounds containing silver, lead, or mercury ions are insoluble in water, and most salts containing group 2A ions have limited solubility in water. Writing Chemical equations for Hydration of an Ionic Compound

A chemical equation can be used to describe the hydration of an ionic compound. The formula unit for the ionic compound and the molecular formula for water, and their physical states, are written on the left side of the equation. The hydrated ions, with their charges, are written on the right side of the equation. Hydration is indicated by including “aq” following the ions. For example, the equation for the hydration of sodium chloride, NaCl, illustrated in Figure 8-10, is shown below: NaCl 1s2 1 H2O 1l2 h Na1 1aq2 1 Cl2 1aq2

When the formula unit for an ionic compound contains subscripts, the subscript indicates the number of that particular ion released into solution and, therefore, must appear as a coefficient on the right side of the equation. For example, when calcium chloride, CaCl2, is added to water, two chloride ions and one calcium ion are hydrated for every one CaCl2 formula unit. Thus, we write the coefficient “2” before the chloride ion on the right side of the equation: CaCl2 1s2 1 H2O 1l2 h Ca21 1aq2 1 2 Cl2 1aq2

Do not write Cl2 (an element) as a product, as it is quite different from two chloride ions, 2 Cl2 . Figure 8-11 Immersing electrodes attached to a battery and a lightbulb into a strong electrolyte. The charged ions in solution complete the electrical circuit and light up the bulb. [2009 Richard Megna – Fundamental Photographs]

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electrolytes

Ionic compounds dissolved in aqueous solution are known as electrolytes. Electrolytes conduct electricity, as demonstrated by placing two electrodes, connected to a lightbulb and a battery, into the solution of dissolved ions (Figure 8-11). When electricity from the battery is supplied,

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8. 2 • SOluTIOnS: DISSOlvIng COvalenT anD IOnIC COMpOunDS

the ions in solution complete the electrical circuit and the lightbulb turns on. A bright light is evidence of a strong electrolyte. Ionic compounds with low solubility in water, like magnesium hydroxide, are classified as weak electrolytes. They result in a dimly lit lightbulb. In the next chapter, we will see other examples of weak electrolytes. When electrodes are inserted into pure water or an aqueous solution containing a dissolved covalent compound, the lightbulb does not turn on. An aqueous solution containing a dissolved covalent compound forms no ions in solution, and therefore, is a nonelectrolyte. Electrolytes play an important role in human physiology. Sodium ions, Na1 , and potassium ions, K1 , are involved in regulating blood pressure and the transmission of electrical signals in neurons (nerve cells). Other physiologically important electrolytes are Ca21 , Mg21 , Cl2 , HPO422 , and HCO32 . Sports drinks such as Gatorade, Propel, and Vitamin Water contain electrolytes. Sports drinks are intended to replenish essential electrolytes lost during physical exertion. Pedialyte (Figure 8-12), recommended for infants and young children, replenishes essential electrolytes lost from prolonged diarrhea and vomiting during an illness. Proper electrolyte balance is regulated by hormones, with the kidneys playing a key role in eliminating excess electrolytes. A routine blood test measures the concentration of the important electrolytes. When electrolyte concentrations are outside the normal range it is often an indicator of organ malfunction. In the next section, we describe how solution concentrations are calculated.

Worked exerCise

Core ConCept: Electrolytes are ions dissolved in aqueous solution, which conduct electricity. Covalent compounds dissolved in solution are nonelectrolytes.

Figure 8-12 Pedialyte is recommended for infants and small children after prolonged diarrhea or vomiting to replenish essential electrolytes. [Catherine Bausinger]

Writing equations for the hydration of ionic Compounds

8-6 What ions are dissolved in solution when sodium phosphate, Na3PO4, is added to

water? Describe what happens during hydration by writing the chemical equation.

solution:

Sodium ion, Na1 , and phosphate ion, PO432 , a polyatomic ion, break apart from the crystalline solid to form ion-dipole interactions with water. Since there are three Na1 ions for every one PO432 ion, we insert a 3 as a coefficient before Na1 on the product side of the equation. Na3PO4 1s2 1 H2O 1l2 h 3 Na1 1aq2 1 PO432 1aq2

Worked exerCise 8-7

ion-dipole interactions

When a sample of potassium iodide, KI, is added to water, it looks like the solid is “disappearing.” Explain what is happening on the molecular level. Provide an illustration showing ion-dipole interactions. Is this solution a strong, weak, or nonelectrolyte? Explain.

solution:

The ionic bonds between K1 and I 2 in the solid crystalline lattice are broken, the ions separate, and the ionic bonds are replaced by ion-dipole interactions between each ion and several water molecules, as shown below. The partial negative charge on several water molecules surrounds the potassium cation, and the partial positive charge on several water molecules surrounds the iodide anion.

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The solution of KI is a strong electrolyte because the solution contains dissolved ions, K1 and I 2 , in solution. +

+ +

H H

– –

–

K+

–

O H +

H H

H +

H O

–

I–

H H

H O

–

Worked exerCise hydration of Covalent and ionic Compounds 8-8 What is the difference between a covalent compound and an ionic compound

when dissolved in water?

solution:

Covalent bonds do not break when a covalent compound is dissolved in water; only intermolecular forces of attraction are broken and new ones with the solvent are formed. Ionic bonds break when an ionic compound is dissolved in water, releasing the charged ions of the crystalline solid into solution, and forming ion-dipole interactions between individual ions and many water molecules.

prACtiCe exerCises

11 12

Which of the following solutes would you expect to dissolve in water, and why? Refer to Table 8-3 if necessary a. NaCl d. CH3OH b. CCl4 e. acetic acid, CH3CO2H c. gasoline 1CxHy 2 f. Na3PO4 For the following ionic compounds, write the chemical equation for hydration. Remember to include the appropriate coefficients. a. MgCl2 b. K3PO4 c. NaHCO3 For the following solutes in aqueous solution, indicate whether it is an electrolyte or a nonelectrolyte, and why. Refer to Table 8-3 if necessary. a. sugar c. ethanol, CH3CH2OH b. KCl d. CaCl2

8.3

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solution Concentration

In this section we describe the preparation of solutions, calculation of concentration, and related calculations. Figure 8-13 shows solutions with increasing concentrations of a blue-colored solute in the same volume of solution. The lighter-colored solutions contain less solute and are said to be more dilute; the darker-colored solutions contain more solute and are said to be more concentrated. Reporting the concentration of a solute in a solution is done routinely in the laboratory and the clinic. A blood test is essentially a sophisticated technique for determining concentrations of various blood solutes.

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8.3 • SOluTIOn COnCenTr aTIOn

Knowing how to work with concentrations is an important part of a health care professional’s responsibilities, including administering the proper dosage of a medicine or setting the IV flow rate of a solution with a given concentration. The concentration of a solute is a quantitative measure of the amount of a solute (mass or moles) in a given volume or mass of total solution. Thus, concentration is a ratio, where the numerator represents the amount of the solute and the denominator represents either the mass or volume of the total solution (solute 1 solvent). In this text, we limit our discussion to concentrations that involve solution volume in the denominator: Solute concentration 5

267

Core ConCept: Concentration is a quantitative measure of the amount of solute, as a unit of mass or moles, per volume of total solution.

Amount of solute Volume of solution

Since concentration is a ratio, the units of concentration are also a ratio. A variety of units are used to represent the amount of solute and the total volume of solution. The units of concentration most commonly encountered in the medical field are as follows: • • • •

mass/volume (m/v) % mass/volume (% m/v) moles/liter (M) equivalents/liter (eq./L)

Preparing a Solution with a Given Concentration A solution is prepared using a volumetric flask, as shown in Figure 8-14a. To prepare a solution with a given concentration, the solute is weighed (Figure 8-14b) and then transferred to an appropriately sized volumetric flask (Figure 8-14c). Solvent is then added to the fill mark on the neck of the volumetric flask, while swirling the flask (Figure 8-14d). This ensures that the mass of the solute and the total volume of solution is known precisely.

Core ConCept: To prepare a solution with a specified concentration, the solute is weighed, added to an appropriately sized volumetric flask, and then solvent is added to the volume mark on the flask and swirled.

Figure 8-14 Preparation of a solution with a known concentration of solute: (a) Obtain an appropriately sized volumetric flask, (b) calculate and weigh the amount of solute needed (solid or liquid), (c) transfer the solute to the volumetric flask, and (d) add solvent to the fill mark on the volumetric flask while swirling to dissolve. [Catherine Bausinger]

(a)

(b)

(c)

(d)

In preparing a solution, it is important to remember that concentration is defined in terms of the volume of total solution, not just the volume of the solvent. For example, to prepare a 5 g/L aqueous solution of sodium chloride, we cannot simply add 5 grams of sodium chloride to 1 liter of water, because the solute also occupies volume and, therefore, would produce a solution with a volume greater than 1 L. A solution prepared in this way would have a concentration less than 5 g/L.

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Mass/Volume Concentration Medications administered in solution form often have their concentration given as a mass per volume (m/v) concentration, where the medicine is the solute. The formula for calculating the concentration of a solution as a mass per volume is shown below: Core ConCept: A common unit of concentration is mass/volume (m/v) where the mass of solute is given in any metric mass unit and the volume of solution is given in any metric unit of volume.

m>v 5

Mass of solute Volume of solution

Calculating the m/v concentration requires the mass of the solute in any metric unit of mass and the volume of solution in any metric unit of volume. Blood tests normally report glucose, cholesterol, and creatinine concentrations in units of mg/dL or mg>dL and protein in units of g/dL. For example, a blood urea concentration of 20.2 mg>dL means there are 20.2 milligrams of urea (the solute) in every one deciliter of blood (the solution). Depending on the amount of solute, different metric prefixes are chosen as shown in Figure 8-15.

Figure 8-15 Blood test results showing concentration units in mg/dL and g/dL. The last two columns show the normal concentration range for each solute. The first row shows the concentration of urea as 20.2 mg/dL. [piotr_pabijan/ Shutterstock.com]

Core ConCept: A m/v concentration can be used as a conversion factor when solute mass or solution volume is given and the other is asked for.

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Since concentration is a ratio, it can be used as a conversion factor in calculations where the amount of solute or the volume of solution is given and the other is requested. The “/” in the concentration unit means “per,” or “for every.” Dimensional analysis, introduced in chapter 1, is used to perform calculations using mass per volume as a conversion factor. Examples of these types of calculations are shown in the Worked Exercises below. Note that in medicine the deciliter (dL) is such a common unit of volume that it is useful to remember the conversion between the dL and the mL: 100 mL 5 1 dL

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8.3 • Solution Concentr ation

Worked Exercises

269

Calculations with Mass/Volume Concentration

8-9 The concentration of an IV l-dopa solution, used to treat Parkinson’s disease,

contains 300. mg l-dopa in 250. mL of total solution. What is the m/v concentration of this solution in milligrams per milliliter (mg/mL)?

Solution:

You are given the mass of the solute, 300. mg, and the volume of solution, 250. mL. You are asked for the concentration in mg/mL. Use the mathematical formula given above for mass/volume concentration and substitute the given values into the equation. Then solve: 300. mg Mass of solute 5 5 1.20 mg>mL Volume of solution 250. mL The final answer, as requested, has units of mg/mL, an m/v concentration unit. 8-10 A patient is prescribed a 50 mg dose of a medicine that is available only as a

10 mg/mL aqueous solution. What volume of the solution, in milliliters, should be administered to the patient?

Solution:

You are given the concentration of the solution, 10 mg/mL, and you are given the mass of the solute, 50 mg. You are asked for the volume of solution. Concentration is a conversion factor, and a conversion factor can be used as is or in its inverted form. Using dimensional analysis, write the given mass of the solute, 50 mg, and multiply by the correct form of the conversion factor that allows mg to cancel, leaving only mL, the asked for unit. The inverted form of concentration is needed to cancel units of mg and obtain an answer in units of mL. 50 mg 3

Math Tip: Remember that a concentration of 10 mg/mL should be 10 mg 1 ml written as 1 ml or 10 mg in a calculation.

1 mL 5 5 mL of solution 10 mg

You would administer 5 mL of the available 10 mg/mL solution of medicine to the patient. 8-11 What is the mass, in milligrams, of l-dopa in 50 mL of a solution of l-dopa with

a concentration of 1.2 mg/mL?

Solution:

You are given the volume of solution, 50 mL, and the concentration of the solution, 1.2 mg/mL. You are asked for the milligrams of l-dopa, the solute mass. Using dimensional analysis, write the volume of the solution, 50 mL, and multi1.20 mg 1 mL b ply by the form of the concentration conversion factor a or 1 mL 1.20 mg that allows units of mL to cancel, leaving only units of mg. 50 mL 3

1.20 mg 1 mL

5 60 mg

Thus, 50 mL of the solution contains 60 mg of l-dopa. 8-12 For an aqueous solution with a chloride ion concentration of 137 mg>dL, what is

the m/v concentration in units of g/mL?

Solution:

You are given a concentration in one set of metric units and asked for the concentration in another set of metric units. Therefore, two metric conversions are needed: one for the numerator 1mg to g2 and one for the denominator (dL to mL).

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8 • Mixtures, Solution Concentrations, Osmosis, and Dialysis

We can simplify the calculation if we remember that 100 mL 5 1 dL. Write the given concentration and multiply by the two required metric conversions, in any order: 1026 g 1 dL 3 3 5 1.37 3 1026 g>mL 1dL 100 mL 1 mg

137 mg

prACtiCe exerCises

13 14 15 16 17

Isuprel, used to treat asthma, is available in IV form as 4 mg per 500 mL of solution. What is the concentration of this solution in mg/mL? Hint: only a division operation is required. Lidocaine, a common local anesthetic, is available in IV form at a concentration of 4 g/L. What is the concentration of this solution in milligrams per deciliter? An aqueous solution of glucose has a concentration of 9.9 mg/dL. What is the mass of glucose, in milligrams, in 3.5 dL of this solution? A blood sample has an iron concentration of 122 mg/dL. What volume of solution, in deciliters, contains 28 mg of iron? A doctor orders 25.0 mg of lidocaine be given to a patient by IV. An IV lidocaine solution is available with a concentration of 4.00 mg/mL. How many milliliters of lidocaine solution should you administer to the patient?

% Mass/Volume Concentration Another concentration unit similar to mass/volume (m/v) is percent mass/ volume (% m/v). To calculate a % m/v concentration, the mass of the solute must be in grams (g) and the volume of solution must be in milliliters (mL). The mass/volume is then calculated and multiplied by 100 to obtain a percentage, as shown in the equation below. % m/v 5

g solute mL solution

3 100

For example, the most common IV solution, physiological normal saline, has a sodium chloride concentration of 0.90% m/v (Figure 8-16), which means 0.90 g of NaCl per 100 mL of solution. Table 8-4 lists some other common IV solutions and the concentration of their solutes, printed on the label as a % mass/volume. These IV solutions are used routinely to treat dehydration and electrolyte imbalances.

Figure 8-16 The most common intravenous (IV) solution is physiological normal saline, which has a sodium chloride concentration of 0.90%.

table 8-4

solute Concentrations of some Common iV solutions

Common Name

Solution Concentration

normal saline (nS)

0.90% naCl

[dtimiraos/Getty Images]

Half-normal saline (1/2 nS)

0.45% naCl

MAth tip: remember, the symbol % means “per 100,” or “divided by 100,” or “for every 12 100.” For example, 12% means 100 or 12 out of 100.

D5W

5% dextrose

D5nS

5% dextrose, 0.9% naCl

lactated ringer’s (lr)

0.60% naCl, 0.31% sodium lactate, 0.03% KCl, 0.02% CaCl2

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Calculating % m/v from a solute mass and solution volume

Calculating a % m/v concentration when given the mass and the volume of a solution is similar to calculating a m/v concentration, except that the units must be given in or converted to g/mL. If not given in grams of solute and milliliters of solution, metric conversions are required. Then, multiply the ratio by 100 to obtain a percentage. For example, to calculate the % m/v concentration of a solution containing 25 mg of glucose dissolved in 50. mL of total solution, follow the two steps below.

Core Concept: A % m/v concentration must be calculated from grams of solute and milliliters of solution. The decimal value is then multiplied by 100 to obtain a percentage (%). To use % m/v as a conversion factor, first convert it to a m/v ratio.

(1) Convert the mass of the solute from units of mg to units of g, a metric conversion: 25 mg 3

1023 g 1 mg

5 0.025 g

(2) Substitute the mass, in grams, and the volume, in milliliters, into the % m/v concentration equation given on page 270: 0.025 g 50. mL

3 100 5 0.050% m>v

Calculating Solute Mass or Solution Volume using a % m/v concentration

In calculations where a % m/v concentration is given, express the % m/v in units of g/mL. To do this, think of % as “per 100.” For example, 2% means 2 g>100 mL: 2% 5

2g 100 mL

Alternatively, you can convert the fraction into its decimal value: 2% 5

2g 100 mL

5 0.02 g>mL

then, use dimensional analysis as shown previously for m/v calculations. For example, to calculate the mass of sodium chloride in 500 mL of a 0.90% m/v sodium chloride solution, write the given volume, 500 mL, and multiply by the appropriate form of the m/v concentration conversion factor, 0.90 g/100 mL: 500. mL 3

0.90 g 100 mL

5 4.5 g of NaCl

Worked Exercises Calculations Involving % m/v 8-13 A solution is prepared by dissolving 0.15 g of NaCl in enough water to produce a

total volume of 275 mL. What is the concentration of this solution in % m/v?

Solution:

You are given the mass of solute, 0.15 g, and the volume of solution, 275 mL. You are asked for the concentration as a % m/v. The equation that defines % m/v concentration is given below. % m>v 5

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grams solute mL solution

3 100

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8 • Mixtures, Solution Concentrations, Osmosis, and Dialysis

Since the given values are in units of grams and milliliters, as required, they can be s ubstituted directly into the equation and solved: 0.15 g 275 mL

3 100 5 0.055%

8-14 What is the mass of solute, in grams, in 3.0 L of a 5.0% m/v aqueous IV dextrose

solution?

Solution:

You are given the volume of solution, 3.0 L, and the concentration of the solution in % m/v, 5.0%. You are asked for the mass, in grams of solute. To use a % m/v concentration as a conversion factor, you must first convert the percentage into a m/v concentration: 5.0% 5

5.0 g 100 mL

Since the volume is given in liters, it must be converted into milliliters so that it can cancel with the volume in the m/v concentration. Using dimensional analysis, write the given volume and multiply by the metric conversion that allows liters to cancel and leaves units of mL. Then, multiply by the m/v concentration conversion factor that allows units of mL to cancel and leaves units of grams, g, of solute remaining: 3.0 L 3

Given

5.0 g 1 mL 3 5 150 g 23 10 L 100 mL

Metric conversion

m/v Concentration

8-15 What volume, in milliliters, of a 10.% solution of sugar contains 3.5 g of sugar? Solution:

You are given the mass of the solute, 3.5 g, and the concentration as a % m/v, 10.%. You are asked for the volume of solution, in milliliters. Express the % m/v as a m/v concentration, which can then be used as a conversion factor: 10.% 5

10. g 100 mL

Using dimensional analysis, write the given mass, 3.5 g, and multiply by the correct form of the concentration conversion factor that allows grams to cancel, leaving only units of mL: 3.5 g 3

100 mL 5 35 mL 10. g

Note that here the inverted form of the m/v conversion factor was used.

PRACTICE EXERCISES

18 19 20

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Calculate the concentration in % m/v of a beverage that contains 28 g of sucrose in 315 mL of the beverage. What volume, in milliliters, of a physiological saline solution contains 2.50 g of NaCl? Assume a physiological saline solution has a concentration of 0.900% m/v. What is the mass of sodium chloride, in grams, of 1.0 L of a 0.45% NaCl solution used for IV therapy? (A metric conversion is involved in this calculation.)

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273

parts per million (ppm) and parts per billion (ppb)

We have seen that a percent concentration (% m/v) is the ratio of grams of solute per milliliters of solution (m/v) multiplied by 100. Very dilute solutions often have concentrations reported in parts per million (ppm), which is the m/v ratio multiplied by one million 1106 2. Solutions with only trace amounts of solute are often reported in parts per billion (ppb), which is the m/v ratio multiplied by one billion 1109 2. Concentrations given in ppm and ppb avoid the many zeros before the decimal that would otherwise result if a very dilute solution were reported in % m/v. For example, a solution with a concentration of 0.000 000 1 g/mL is expressed as a %, a ppm, and a ppb in Table-8-5. Table 8-5 Expressing g/mL as a %, a ppm, or a ppb Concentration Unit % ppm ppb

Calculation 5

g 3 100 ml

g 3 106 ml g 5 3 109 ml

Example: 0.000 000 1 g/mL 5 0.000 01 % 5 0.1 ppm 5 100 ppb

We see ppm and ppb used routinely to report concentrations of very dilute solutions. For example, to reduce the incidence of tooth decay, fluoride is added to many municipal water supplies at a concentration of 1 ppb. Parts per billion, ppb, is also a common unit for reporting the safe limit of some hazardous compounds and elements. For example, the Environmental Protection Agency (EPA) has set the maximum allowable concentration of mercury (Hg) in drinking water at 2 ppb.

WORKED EXERCISES Comparing m/v, % m/v, ppm, and ppb 8-16 For a solution with a concentration of 0.000 045 g/mL (m/v), express the concen-

tration as a % m/v, a ppm, and a ppb. Which concentration is easiest to report because it has the fewest zeros?

Solution:

Use the equations in the second column in Table 8-5: 0.0045 %; 45 ppm (fewest zeros, easiest to report); 45,000 ppb 8-17 The EPA maximum allowable concentration of lead (Pb) in drinking water is

5 ppb. Express this concentration in g/mL, % m/v, and ppm.

Solution:

First, convert 5 ppb into an m/v concentration: 5 g>109 mL 5 0.000 000 005 g>mL. Then, substitute this value into the appropriate equations in Table 8-5 to obtain a % m/v and a ppm: 0.000 000 5%, 0.005 ppm.

PRACTICE EXERCISE

Rank the following solutions from most concentrated to least concentrated. a. 5 ppm b. 5% c. 1 ppb d. 5 ppb

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Molar Concentration Another common unit of concentration is molar concentration, also known as molarity. The molar concentration of a solution is defined as the moles of solute per liter of solution, abbreviated M. Molarity is calculated using the equation below. The unit of volume for molar concentration is always liters (L). Core Concept: Molar concentration represents the moles of solute per liter of solution, mol/L, and has the abbreviation M.

Molarity (M) 5

Moles of solute Liters of solution

Molar concentration is the preferred unit of concentration in chemistry because the amount of solute is expressed in moles, a unit that indicates the number of solute particles (atoms, molecules, or formula units) per liter of solution. For example, a 1 M aqueous solution of methanol has the same number of methanol molecules as a 1 M aqueous solution of glucose has glucose molecules; both contain 6.02 3 1023 molecules in a liter of solution. Molar concentration, and the related unit “equivalents per liter,” is used to report the amount of various substances measured in a blood test, such as the concentration of carbon dioxide, and calcium, sodium, potassium, and chloride ions. For dilute solutions, millimoles per liter (mM) or milliequivalents per liter (meq./L) are used instead. Recall from chapter 1 that milli is the prefix that represents the multiplier 1023. Therefore, 1mmol 5 1023 mol. The process for performing calculations involving molar concentration is much the same as described for m/v calculations. However, when molar concentration, M, is used as a conversion factor, replace M with mol/L; otherwise, units will not cancel. Also, do not confuse M and mol, as they are different units.

Worked Exercises Molarity Calculations 8-18 A solution with a total volume of 1.5 L contains 0.018 mol of carbon dioxide

1CO2 2. What is the molar concentration of carbon dioxide in this solution?

Solution:

You are given the moles of solute, 0.018 mol, and the volume of solution, 1.5 L. You are asked for the molar concentration, M. First, check that the solution volume is in liters. Then, substitute the given values into the equation for molar concentration and solve. Molarity (M) 5

Moles of solute Liters of solution

0.018 mol 5 0.012 mol>L 5 0.012 M 1.5 L We replace the units mol/L with the abbreviation for molarity M. Also, remember to include the correct number of significant figures in the final answer based on the measurement with the least number of significant figures. 8-19 How many moles of glucose are in 500. mL of a 0.50 M aqueous solution of

glucose?

Solution:

You are given the volume of solution, 500. mL, and the molar concentration of glucose, 0.50 M. You are asked for the moles of glucose. Express the concentration as 0.50 mol/L. Using dimensional analysis, write the given volume and then

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multiply by the metric conversion factor that converts the volume from units of mL to units of liters. Then, multiply by the form of the concentration conversion factor that allows liters to cancel, leaving moles: 500. mL 3 Given volume

1023 L 0.50 mol 3 5 0.25 mol glucose 1 mL 1L

Metric conversion

Molar concentration

8-20 What volume, in milliliters, of a 0.5 M aqueous solution of glucose contains

0.2 mol of glucose?

solution:

You are given the moles of solute, 0.2 mol, and the molar concentration of glucose, 0.5 M. Replace M with mol/L, thus 0.5 M is 0.5 mol/L. You are asked for the volume of solution in milliliters. Using dimensional analysis, write the given moles of solute, 0.2 mol. Next, multiply by the inverted form of molar concentration so that moles cancel, leaving only liters. Finally, multiply by the metric conversion that converts liters to milliliters, the asked for unit. 0.2 mol 3 Given moles

1L 1 mL 3 23 5 400 mL 0.5 mol 10 L

Inverted Metric molar conversion concentration

prACtiCe exerCises

22 23 24

8.4

A gas mixture with a volume of 3.0 L contains 0.023 mol of oxygen 1O2 2. What is the molar concentration (molarity) of oxygen in this solution? Express your answer using the symbol M. How many moles of lithium ions, Li1 , does 2.5 L of 1.2 M aqueous lithium chloride contain? How many liters of a 1.25 M aqueous glucose solution contains 0.5 mol of glucose?

solution dosage Calculations in Medicine

Many medicines are available, or are more conveniently administered, in solution form. The concentration of these medicines represents the amount of medicine (the solute) in a given volume of solution. In this section, we describe common dosage calculations involving solutions. Dimensional analysis is used and concentration serves as a conversion factor, much like the calculations in section 8.3.

Administering Solutions of Oral Medications Medicines given by mouth—oral medications—are often administered in solution or suspension form. For example, NyQuil Cold & Flu is an overthe-counter solution containing four active pharmaceutical ingredients, the important solutes. The concentration of acetaminophen is 21.7 mg/mL (Figure 8-17). The recommended dose of NyQuil is 15.0 mL every 6 hours. From the m/v concentration, we can calculate that a patient receiving a 15.0 mL dose of NyQuil has been given 326 mg of acetaminophen: 15.0 mL 3

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21.7 mg 1 mL

5 326 mg acetaminophen

Figure 8-17 NyQuil, an overthe-counter oral medication, is an aqueous solution containing the analgesic acetaminophen. [Catherine Bausinger]

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Worked exerCise

dosage Calculations with solutions and suspensions

8-21 Amoxicillin is an antibiotic available as a suspension with

rvlsoft/Shutterstock

a concentration of 200. mg/5.00 mL. A doctor orders that 500. mg of amoxicillin be administered to your patient every 6 hours. What volume of this suspension should you administer to your patient every 6 hours? Why should the suspension be shaken before dispensing?

solution:

You are given the mass of the medicine (the solute), 500. mg of amoxicillin, and the concentration of the suspension, 200. mg/5.00 mL. You are asked for the volume of the suspension. Note that a suspension is analogous to a solution for the purposes of a calculation. Using dimensional analysis, write the mass of the solute and multiply by the form of the concentration conversion factor that will allow milligrams to cancel, leaving only the volume of the suspension: 500.mg 3 Mass of solute

5.00 mL 5 12.5 mL of suspension every 6 hours 200.mg

Inverted concentration

The suspension should be shaken before dispensing because the particles of a suspension settle upon standing. The concentration of amoxicillin is uniform throughout the mixture only after mixing.

prACtiCe exerCises

25 26

An order is given for 60. mg of Tylenol to be administered to a patient every 4 hours. The pharmacy supplies Tylenol as a 40. mg/mL solution. How many milliliters of the Tylenol solution should you administer to the patient every 4 hours? Tegretol is used as an anticonvulsant and mood-stabilizing drug. An order is given to administer 250. mg as needed. The medicine is available only as a solution with a concentration of 20.0 mg/mL. How many milliliters of the Tegretol solution should be administered to the patient? An order is given to administer 20 mg of Atarax, an antihistamine, every 4 hours. Atarax is available as a 2 mg/mL solution. How many milliliters of the solution should be administered to the patient every 4 hours?

IV Solutions and Flow Rate Intravenous (IV) administration of a solution directly into a vein is often used to deliver a pharmaceutical over a period of time. This is necessary when the pharmaceutical is rapidly metabolized, unstable, or when oral administration is not possible, as in the case of an unconscious patient. To administer a pharmaceutical by IV, the solution is infused into the vein at a specific volume per unit of time, known as a flow rate, as defined in the equation below: Core ConCept: A flow rate is the solution volume per unit time that a solution is administered into a vein by IV.

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Flow rate 5

Solution volume Time

A rate refers to a ratio where time is in the denominator, such as miles per hour (the speed of a car) or milliliters per minute (a flow rate). A flow rate

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277

can be calculated from the rate the medicine should be administered, which is usually prescribed by the physician. Rate medicine administered 5

Solute mass 1medicine2

Time The rate a medicine should be administered is usually given in units of g/hr, mg/min, or mcg/min. Rates are conversion factors. Therefore, they can be used as is or in their inverted forms. For example, multiplying concentration by flow rate gives the rate the medicine is administered (solution volume cancels): Solute mass Solution volume Solute mass 3 5 Solution volume Time Time (Concentration)

(Flow rate)

5 (Rate medicine administered)

Similarly, multiplying the inverted form of concentration by the rate the medicine is administered gives the flow rate (solute mass cancels): Solution volume Solute mass Solution volume 3 5 Solute mass Time Time (Inverted concentration)

(Rate medicine administered)

(Flow rate)

Again, dimensional analysis guides us through these types of calculations by focusing on the units.

Worked exerCises iV solution Calculations at right. An order is given to infuse 50. units of heparin per hour. At what flow rate, in milliliters per hour, should the IV solution be infused into the patient? Protein concentrations are often reported in international units, IU, or simply “units.” Treat international units just like you would the mass of a solute.

solution:

You are given the rate at which the medicine should be administered: 50. units/hr (remember, “/” reads as “per” and means “divided by”). You are also given the solution concentration: 25,000 units/500 mL. You are asked for the flow rate in mL/hr. Begin by writing both given conversion factors and their inverted forms. Rate medicine administered: Concentration:

50. units 1 hr

1 hr 50. units

Scott Linnett/ZUMA Press/Newscom

8-22 IV solutions of heparin are available as 25,000 units/500 mL of solution, as shown

25,000 units 500 mL or 500 mL 25,000 units

Since you are being asked for the flow rate in units of mL/hr, select the only conversion factor that has mL in the numerator and multiply by the only conversion factor that has hr in the denominator. “Units” cancel, leaving the asked for units, mL/hr, the flow rate: 500 mL 50. units 1 mL 3 5 5 1 mL>hr 25,000 units 1 hr hr inverted 3 rate medicine concentration administered

5 flow rate

8-23 Isuprel is used to treat asthma, chronic bronchitis, and emphysema. A patient is

receiving 30. mL/hr of an 8 .0 mg >mL solution of Isuprel in D5W. How many micrograms per hour is the patient receiving?

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You are given the flow rate, 30. mL/hr, and the concentration of the medicine, 8.0 mg>mL. You are being asked for the rate at which medicine is administered in mg>hr. Write the two given conversion factors and their inverted forms, and then determine which two conversion factors you need—that is, the conversion factors that contain the numerator and the denominator of the asked for rate medicine is administered, mg>hr. Flow rate:

30. mL 1 hr

Concentration:

8.0 mg 1 mL

1 hr 30. mL or

1 mL 8.0 mg

Using dimensional analysis, multiply the conversion factor that has micrograms in the numerator by the conversion factor that has hours in the denominator so that mL cancel, and mg>hr remain: 8.0 mg 1 mL

mg 30. mL 5 240 1 hr hr

Concentration 3 Flow rate 5 Rate Isoprel administered

PRACTICE EXERCISES

Digoxin is used to treat a variety of heart conditions, such as heart failure and atrial fibrillation. An order is given to administer 200. mg of digoxin every 5 min by IV. The digoxin solution concentration is 2.5 mg>mL. What should you set the flow rate to in milliliters per minute? Droperidol is used to treat postoperative nausea. An order is given to administer 0.275 mg droperidol over 3.0 hr by IV. The IV solution has a concentration of 2.5 mg/mL droperidol. What should you set the flow rate to in milliliters per hour? A diabetic patient suffering from hyperglycemia is receiving an insulin solution by IV at a flow rate of 25 mL/hr. The concentration of the insulin solution is 0.4 unit/mL. How many units of insulin per hour is the patient receiving?

8.5 Solution Dilution Calculations Core Concept: Solutions can be prepared from more concentrated solutions, a process known as dilution.

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You learned earlier in the chapter how to prepare solutions by adding a pure solute to the appropriate amount of solvent using a volumetric flask. A solution can also be prepared from a more concentrated solution by dilution. Preparing a solution by dilution is necessary when solutes are not readily available in their pure form but are available as stock solutions—commercially available concentrated solutions with a known concentration. For example, preparation of an aqueous solution of hydrochloric acid, HCl, from pure HCl is difficult because HCl is a gas at room temperature. However, concentrated aqueous solutions of HCl are commercially available at a concentration of 12 M, known as concentrated hydrochloric acid.

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To prepare a solution from a more concentrated solution use the dilution equation below.

MAth tip: recall from algebra that when you have one equation, you can only solve for one unknown. If you have two equations, then you can solve for two unknowns.

C1 3 V1 5 C2 3 V2 where C1 5 the concentration of the more concentrated solution (stock solution), V1 5 the volume of the more concentrated solution (stock solution), C2 5 the concentration of the dilute solution, V2 5 the volume of the dilute solution. To use this equation, three of the four variables must be given, and then you can solve for the fourth, unknown variable. When using the solution dilution equation, C1 and C2 can be any unit of concentration, provided the units are the same: m/v, % m/v, M. Similarly, the volume can be any volume unit, provided the units are the same. For example, if molarity, M, is the concentration unit, the solution dilution equation can be rewritten as shown below. The steps for solving a solution dilution calculation are described in the Guidelines: Solving a Solution Dilution Problem.

Core ConCept: The dilution equation C1V1 5 C2V2 can be solved for any variable, provided the other three variables are given.

M 1 3 V1 5 M 2 3 V2

Guidelines

Solving a Solution Dilution Problem

Example: To prepare 100 mL of a 1% aqueous saline solution from a 10% aqueous saline stock solution, what volume of the stock solution should be added to a 100 mL volumetric flask? Step 1. Begin by identifying the three given variables and the unknown variable from the information in the question. Read the question carefully to identify the three-of-four variables required in order to use the dilution equation. Look for clues that indicate a reference to the more concentrated or stock solution versus the dilute solution.

C1 5 10% C2 5 1% V1 5 ? V2 5 100 mL

Step 2. Rearrange the dilution equation algebraically, solving for the unknown variable. Divide both sides of the dilution equation by the variable you want to remove from one side of the equation.

The dilution equation: C1 3 V1 5 C2 3 V2 In this example, we want to solve for V1, the unknown, so we divide both sides by C1:

concentration of stock solution concentration of dilute solution volume of the stock solution needed volume of the dilute solution

C1 3 V1 C2 3 V2 5 C1 C1 C2 3 V2 V1 5 C1 Step 3. Substitute the variables identified in step 1 into the algebraically rearranged equation from step 2 and solve for the unknown variable. Substitute the known variables into the rearranged dilution equation. Cancel like units and solve.

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V1 5

1% 3 100 mL 5 10 mL 10%

Transfer 10 mL of the 10% stock solution to a 100 mL volumetric flask and then add water to the fill mark and mix.

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Worked Exercise Solution Dilution Calculations 8-24 A student transferred 50. mL of a 2.5 M aqueous sodium hydroxide stock solution

to a 500. mL volumetric flask and added water to the fill mark. What is the molar concentration of the solution she prepared?

Solution:

Step 1. Identify the three given variables and the unknown variable. C1 5 2.5 M C2 5 ? V1 5 50. mL V2 5 500. mL Step 2. Write the dilution equation. C1 3 V1 5 C2 3 V2 Rearrange the dilution equation algebraically to solve for the unknown variable in step 1. Here, we want to solve for C2 so we divide both sides of the dilution equation by V2. C1 3 V1 C2 5 V2 Step 3. Substitute the given variables identified in step 1 into the rearranged equation in step 2 and then solve for the unknown variable, C2: C2 5

2.5 M 3 50. mL 5 0.25 M 500. mL

The diluted solution has a concentration of 0.25 M.

PRACTICE EXERCISES

What volume of a 2.0 M aqueous glucose solution would you need to add to a 50. mL volumetric flask to obtain 50. mL of a 1.0 M glucose solution? 32 What is the concentration of a solution prepared by adding 10. mL of a 5% saline solution to a 100. mL volumetric flask and adding water to the fill line? 33 What is the molar concentration of a lidocaine solution prepared by diluting 10. mL of a 2.0 M lidocaine stock solution to the mark in a 25 mL volumetric flask?

8.6 Osmosis and Dialysis

Core Concept: The cell membrane is a selectively permeable membrane, allowing water and certain solutes to cross the membrane. Colloids and larger particles cannot cross a selectively permeable membrane.

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In this section, we consider the behavior of solutions separated by a selectively permeable membrane, such as the cell membrane. We describe the permeability of the cell membrane and then consider the two important processes that describe whether solutes can cross a selectively permeable membrane: osmosis and dialysis. Cell membranes are selectively permeable membranes, which means they allow only certain substances to diffuse across the membrane from one side to the other. Colloids and larger particles cannot cross a selectively permeable membrane, ensuring that proteins and the organelles of the cell

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281 Figure 8-18 A cross-section of a cell

Nucleus Mitochondria

showing the cell membrane and other parts of the cell.

Cell membrane

remain inside the cell. A diagram of the cell showing the cell membrane is illustrated in Figure 8-18. Selectively permeable membranes are also found in other parts of the body, such as the nephrons in the kidneys, which filter the blood.

Diffusion and Crossing the Cell Membrane In solution, solutes and solvent molecules are in constant random motion as a result of their kinetic energy. The random movement of solute particles through the solvent is known as diffusion. When a soluble solute is added to a solvent, the solute diffuses through the solution until the concentration is uniform throughout. When two solutions with a different concentration, known as a concentration gradient, are separated by a selectively permeable membrane, solutes cannot simply diffuse across the membrane. To cross the cell membrane, for example, a substance must be able to cross through the two polar regions on the inside and outside of the membrane and the nonpolar section in between. Three factors determine whether a solute can cross the cell membrane: • solute size, favoring smaller substances, • solute charge, favoring neutral substances, and • solute polarity, favoring less polar substances. Figure 8-19 shows that the substances most able to cross a cell membrane are small neutral nonpolar molecules such as oxygen 1O2 2, nitrogen 1N2 2, and carbon dioxide 1CO2 2. Although water 1H2O2 is polar, its small size and neutral charge allows it to readily cross a selectively permeable membrane. Larger polar neutral molecules, like glucose 1C6H12O6 2, require assistance to cross the cell membrane. Small monatomic ions such as chloride ion 1Cl2 2, sodium ion 1Na1 2, and potassium ion 1K1 2 cannot cross the cell membrane because of their full charge. Substances that cannot cross a cell membrane are large polyatomic ions and very large neutral molecules like colloids, such as proteins, polysaccharides (large carbohydrates like starch), and fats. Systems that assist compounds and ions in crossing the cell membrane often require energy to do so.

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Core Concept: Substances with a smaller size, neutral charge, and which are less polar are better able to cross the cell membrane.

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Figure 8-19 The ability of a substance to cross the cell membrane depends on its size, charge, and polarity. The smaller, less polar, and more neutral, the better able it is to cross the cell membrane.

Cell membrane

Small, nonpolar molecules

O2, CO2, N2

H2O glycerol

Small, uncharged polar molecules

Glucose, amino acids

Large, uncharged polar molecules

Cl2, K1, Na1, H1

Small monoatomic ions

Proteins, carbohydrates, fats

Large neutral and charged biomolecules

Since ions cannot diffuse across the cell membrane, there are ion concentration gradients between the inside and the outside of the cell. Table 8-6 shows the concentration, in millimoles per liter (mM), of some important ions inside and outside a blood cell. Concentration gradients are essential for the transmission of nerve impulses and other cellular signaling processes. table 8-6 Concentration of Ions Inside and

Outside a Blood Cell Electrolyte na 1 Cl K

Ca21

Worked Exercise

Concentration Inside the Cell (mM)

Concentration Outside the Cell (mM)

140

100

140

1 3 1024

2.5

The Ability of Ions and Molecules to Cross a Selectively Permeable Membrane

8-25 Which ion or molecule in each pair is better able to cross the cell membrane?

Explain. a. chloride ion, Cl2 , or a molecule of glucose, with its six O i H bonds b. glucose 1C6H12O6 2 with its six O i H bonds or water 1H2O2 c. oxygen, O2, or potassium ion, K1

Solution:

a. Glucose. It is a small polar neutral molecule, which is better able to cross a selectively permeable membrane than a monatomic ion, which has a full charge. b. Water. Both are polar and neutral molecules, but water has a smaller size. c. Oxygen. Oxygen is far better able to cross the cell membrane because it is neutral and nonpolar whereas potassium ion has a full charge.

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PRACTICE EXERCISES

34 35

Why are proteins unable to cross the cell membrane without assistance? Which solute/colloid in each pair is better able to cross the cell membrane, and why? a. calcium ion, Ca21 , or a small, neutral amino acid molecule b. water 1H2O2 or sodium ion, Na1 c. carbon dioxide, or potassium ion, K1 d. starch (a colloid) or glucose (a small polar solute). Both substances are neutral.

Osmosis When a concentration gradient exists between two solutions separated by a selectively permeable membrane and solute cannot cross the membrane, water diffuses across the membrane from the solution with the lower solute concentration to the solution with the higher solute concentration until both solution concentrations are the same. This process is known as osmosis. For example, when seawater is separated from fresh water by a selectively permeable membrane (Figure 8-20a), water from the freshwater side (fewer ions) diffuses across the selectively permeable membrane to the seawater side (more ions) by osmosis. The volume of seawater increases and the volume of fresh water decreases after osmosis as illustrated in Figure 8-20b. Before osmosis

After osmosis

Selectively permeable membrane

Selectively permeable membrane Fresh water

Seawater (a)

Seawater

Core Concept: Osmosis is the diffusion of water across a selectively permeable membrane from the less concentrated solution to the more concentrated solution. The volume of the more concentrated solution increases as a result.

Fresh water (b)

Figure 8-20 (a) A concentration gradient between seawater and fresh water separated by a selectively permeable membrane. (b) During osmosis, water diffuses from the fresh water side to the seawater side equalizing the concentrations and causing an increase in the volume of the seawater.

The external pressure that must be applied to the more concentrated solution to prevent osmosis is known as the osmotic pressure. When the external pressure is greater than the osmotic pressure, it causes water to flow against the concentration gradient (from the more concentrated solution to the less concentrated solution), known as reverse osmosis. In areas of the world where fresh water is scarce, reverse osmosis is used to produce drinking water from seawater. Reverse osmosis is also used to force excess water out of the blood as it is being filtered during hemodialysis, a life-support treatment for individuals with kidney disease. The direction in which water diffuses during osmosis is governed by the total number of solute particles in solution (molar concentration), not their mass or identity. For example, a solution containing 2 mM glucose and 3 mM urea has an osmolarity of 5 mM. Osmolarity is the molar concentration of all the particles in solution that contribute to its osmotic pressure.

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Core Concept: Osmotic pressure is the external pressure that must be applied to the more concentrated solution to prevent osmosis. Reverse osmosis occurs when an external pressure greater than the osmotic pressure is applied, causing water to diffuse against the concentration gradient.

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Tonicity

The terms listed below are used when comparing the concentrations of two solutions separated by a selectively permeable membrane. • Hypertonic solution: The more concentrated solution • Hypotonic solution: the more dilute solution • Isotonic solutions: solutions with equal concentrations For example, we can use these terms to describe osmosis. Osmosis is the diffusion of water across a selectively permeable membrane from the hypotonic solution to the hypertonic solution until both solutions are isotonic. The hypertonic solution increases in volume as a result of osmosis. Osmosis in Red Blood Cells

Core Concept: IV solutions must be isotonic with red blood cells to maintain the normal volume of the cell. In a hypotonic solution, water enters the cell, causing hemolysis. In a hypertonic solution, water diffuses out of the cell, causing crenation.

When red blood cells are placed in an isotonic solution they maintain their healthy biconcave shape, as illustrated in Figure 8-21a. A person receiving IV fluids is always given a solution isotonic with red blood cells, such as a physiological saline solution, which has a concentration of 0.90% m/v sodium chloride; otherwise, the consequences are life threatening. When a red blood cell is immersed in a hypotonic solution, Figure 8-21b, water diffuses through the cell membrane by osmosis from the hypotonic solution into the cell (hypertonic). Consequently, the volume of the red blood cell increases. Red blood cells immersed in a hypotonic solution will swell until they eventually burst, known as hemolysis.

Cell membrane Extracellular solution

Intracellular solution

(a) Isotonic solution

(b) Hypotonic solution

Water

= solute that cannot cross membrane Figure 8-21 The effect on red blood cells placed into solutions of different tonicity. (a) An isotonic solution: no net flow of water; (b) a hypotonic solution: water flows into the cell; (c) a hypertonic solution: water flows out of the cell. [David M. Phillips/Science Source]

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285

When a red blood cell is immersed in a hypertonic solution, igure 8-21c, water diffuses through the cell membrane from the cell F (hypotonic) into the hypertonic solution. Consequently, the volume of the red blood cell shrinks, known as crenation.

Worked Exercises Osmosis 8-26 Consider aqueous solutions A and B separated by a selectively permeable mem-

brane. The small circles represent solutes that cannot diffuse across the membrane. The system at left is before osmosis and the system at right is after osmosis.

Before osmosis

After osmosis

Selectively permeable membrane

a. Before osmosis, which solution is the hypertonic solution and which solution is the hypotonic solution, A or B? b. After osmosis, label solutions A and B as hypertonic, hypotonic, or isotonic. c. Explain why after osmosis the volume of solution B has increased while the volume of solution A has decreased. d. To which solution in the system at left would you need to apply pressure to prevent osmosis from occurring: solution A or s olution B? Solution:

a. Before osmosis, solution A is hypotonic (more dilute), as indicated by fewer particles in the same volume of solution. Solution B is hypertonic (more concentrated), as indicated by more particles in the same volume of solution. b. After osmosis, both solutions are isotonic, the same concentration. c. Water diffuses across the membrane from solution A to solution B causing the volume of solution B to increase and the volume in solution A to decrease. d. Since water spontaneously diffuses across the membrane from solution A to solution B, as a result of osmosis, pressure would need to be applied to solution B (the hypertonic solution) to prevent osmosis. 8-27 Milk of Magnesia, Mg1OH2 2, works as a laxative by drawing water out of tissues

through osmosis and increasing the water content of the stool. Explain how Milk of Magnesia works in terms of concentrations and osmosis.

Solution:

Consuming Milk of Magnesia increases the number of Mg21 ions and OH 2 ions in the stool, which causes water to cross the selectively permeable membrane of the colon toward the higher ion concentration (hypertonic solution), thereby increasing the amount of water in the stool.

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PRACTICE EXERCISES

For each of the solutions separated by a selectively permeable membrane, shown below before osmosis: i. label each solution as hypertonic, hypotonic, or isotonic. ii. indicate the direction in which water will diffuse across the membrane, if at all, as a result of osmosis. iii. indicate which solution will increase in volume, after osmosis, if at all. (b)

(a)

Selectively permeable membrane

Solution A 0.4 mM glucose

Solution B 0.2 mM glucose

(c)

Solution A 0.1 mM protein 0.2 mM glucose

(d)

Selectively permeable membrane

Solution A pure water

37 38

Solution B 0.2 mM glucose

Selectively permeable membrane

Solution B 0.1 M NaCl

Solution A 1 M KCl

Solution B 1 M HCl

What happens when a red blood cell is placed in a 1.5% m/v solution of sodium chloride? What is “reversed” in reverse osmosis?

Dialysis Core Concept: Dialysis is the diffusion of small solute particles through a dialysis membrane. Solutes diffuse from the hypertonic to the hypotonic solution until both solutions are isotonic.

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Dialysis is the diffusion of small solute particles across a dialysis membrane. A dialysis membrane is a selectively permeable membrane that allows monatomic ions, small molecules, and water to diffuse across the membrane but does not allow colloids, and other large molecules, and large polyatomic ions to cross the membrane. Solutes diffuse across a dialyzing membrane from the hypertonic solution to the hypotonic solution until both solutions are isotonic. Dialysis allows small solutes to be separated from colloids. For example, kidney hemodialysis removes small ions and small molecules from the blood but does not remove proteins (very large molecules) from the blood. Cellophane is a type of dialysis membrane, permeable to water, glucose (a polar molecule), and small ions. Consider a cellophane bag filled with an aqueous mixture containing a protein and sodium chloride, which is immersed in a beaker of pure water (Figure 8-22a). The sodium ions, Na1 , and chloride ions, Cl2 (green dots), diffuse across the cellophane membrane into the surrounding beaker of water until the concentration inside and outside the cellophane bag is isotonic Figure 8-22b. The protein (large red dots), a colloid, cannot cross the dialysis membrane because of its large size, so it remains within the cellophane bag.

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287

Dialysis bag Aqueous mixture Water

Before dialysis

After dialysis

(a)

(b)

Figure 8-22 A cellophane bag acts as a dialysis membrane. (a) An aqueous solution of sodium chloride (green dots) and a protein (red dots) in a sealed cellophane bag are placed into a beaker of water, (b) The sodium and chloride ions cross through the membrane into the beaker of water until the solutions inside and outside the bag are isotonic. The protein molecules remain in the cellophane bag.

Worked Exercise Dialysis 8-28 A dialysis membrane separates mixture A from pure water, as shown in the dia-

gram on the left. Mixture A contains urea (blue circles), a small neutral molecule, and albumin (yellow circles), a protein (a colloid). Show what the two compartments will look like after dialysis in the diagram on the right. Does urea cross the membrane? Does albumin cross the membrane? How do the concentrations compare after dialysis? Before dialysis Mixture A

After dialysis

Pure water

Urea ( ) Albumin ( ) Selectively permeable membrane ( ) Solution:

Since urea is a small neutral solute molecule separated from pure water by a dialysis membrane, only urea will diffuse across the membrane until the total concentration of all particles (yellow and blue) is equal on both sides of the membrane. Urea diffuses from the hypertonic to the hypotonic solution. Albumin is a c olloid, so it is too large to cross the dialysis membrane and remains in mixture A. Before dialysis Mixture A

After dialysis

Pure water

Urea ( ) Albumin ( ) Selectively permeable membrane ( )

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8 • Mixtures, Solution Concentrations, Osmosis, and Dialysis 8-29 How could you remove more urea from mixture A in exercise 8-28? Solution:

To remove more urea from mixture A, you could periodically replace the solution on the right side of the membrane with fresh water. Every time the solution on the right side is replaced with fresh water, dialysis would resume and additional urea would be removed from mixture A.

PRACTICE EXERCISE

Consider two solutions that are separated by a dialysis membrane. One side of the membrane contains a 0.45% saline solution and the other side contains a physiological saline solution (0.90% NaCl). Which solution is hypertonic? Which solution is hypotonic? In which direction will the ions diffuse, and why? How will the concentration of each of the solutions be different after dialysis?

Chemistry in Medicine Hemodialysis—Performing the Function of the Kidneys The kidneys serve the important function of filtering our blood, as described in the Concepts in Context at the beginning of the chapter. Kidney failure, known as renal failure, can occur suddenly, referred to as acute, or it may be of gradual onset (chronic). Acute renal failure can be caused by severe shock, dehydration, a heart attack, or a severe kidney infection. Chronic renal failure can be caused by diabetes, high blood pressure, or certain hereditary factors. A person with less than 15% kidney function must undergo hemodialysis, a life-support treatment that performs the function of the kidneys, until a donor kidney can be found. Hemodialysis removes waste products Figure 8-23 Hemodialysis. Blood is removed through a vein and pumped through a cellulose tube in the dialyzer, where it is filtered by dialysis with a solution of dialysate, and then returned to the body through another vein.

Blood pump

and excess water from the blood, while retaining colloids such as proteins and larger particles such as blood cells. Hemodialysis is typically a 5-hour treatment performed three times a week at a medical center. During the procedure, blood is pumped out of a vein in the forearm and into the dialyzer, which filters the blood much like a kidney. The filtered blood is then returned to the body through another vein, as illustrated in Figure 8-23. The dialyzer contains an aqueous solution, known as the dialysate, that is similar in composition to filtered blood serum but hypotonic (less concentrated) 2 Blood is pumped into a dialyzer

Blood enters the dialyzer

Dialyzer

1 Blood is removed from the body and pumped through a tube 3 Filtered blood is returned to the body

Used dialysate exits Cellulose dialysis membrane

Fresh dialysate enters

Filtered blood exits the dialyzer

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COre COnCepTS

relative to the patient’s blood. In the dialyzer, the patient’s blood flows through a tube made of cellulose, a dialysis membrane. As the patient’s blood is pumped through the dialyzer, ions and other solutes such as urea and creatinine diffuse through the cellulose membrane from the patient’s blood (the hypertonic solution) to the dialysate (the hypotonic solution).

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Urea and creatinine are some of the waste products of metabolism that are removed through dialysis. A typical hemodialysis treatment removes 2–10 liters of dialysate waste. By maintaining a pressure greater than the osmotic pressure of the blood, water from the dialysate cannot enter the blood by osmosis, and excess water can be removed from the blood.

Core Concepts

• Mixtures are composed of two or more elements

and/or compounds.

8.1 Types of Mixtures • A mixture can

be separated into its pure compounds and elements by physical (a) © D. Hurst/Alamy Stock Photo; separation (b) © sciencephotos/Alamy Stock Photo techniques. • The components of a homogeneous mixture are evenly distributed, whereas the components of a heterogeneous mixture are unevenly distributed throughout the mixture. • The main component of a solution is the solvent, and the minor components are the solutes: Solute(s) + Solvent = Solution. • Solutions contain the smallest particles (,1 nm) dissolved uniformly throughout a solvent. • A colloidal dispersion contains colloids, particles which are 1 nm to 1 mm in diameter. • The particles of a suspension are larger than 1 mm. Suspensions are heterogeneous mixtures whose particles settle upon standing. 8.2 Solutions: Dissolving Covalent and Ionic Compounds in a Solvent • “Like dissolves

like” summarizes the observation that polar solutes dissolve in polar solvents and nonpolar solutes dissolve in nonpolar solvents. • During solvation of a polar covalent compound, hydrogen bonds between polar solutes are broken and new ones are formed between the solute and solvent molecules. No covalent bonds are broken.

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• The tendency for a polar and a nonpolar liquid to

separate into two layers is a result of the hydrophobic effect. • A saturated solution contains the maximum amount of solute that can dissolve in a solvent at a given temperature. A supersaturated solution contains more than the maximum amount of solute and appears as a precipitate. • When an ionic compound dissolves in water, ionic bonds are broken and ion-dipole interactions are formed between each of the separated ions and the opposite partial charges on several water molecules. • Electrolytes are ions dissolved in aqueous solution, which conduct electricity. Covalent compounds dissolved in solution are nonelectrolytes. 8.3 Solution Concentration • Concentration is a quantitative

measure of the amount of solute, as a unit of mass or moles, per volume of total solution. • To prepare a solution with a specified concentration, the solute is weighed, added to an appropriately sized volumetric flask, and then solvent is added to the volume mark on the flask and swirled. • A common unit of concentration is mass/volume (m/v) where the mass of solute is given in any metric mass unit and the volume of solution is given in any metric unit of volume. • A m/v concentration can be used as a conversion factor when solute mass or solution volume is given and the other is asked for. • A % m/v concentration must be calculated from grams of solute and milliliters of solution. The decimal value is then multiplied by 100 to obtain a percentage (%). To use % m/v as a conversion factor, first convert it to a m/v ratio. • Molar concentration represents the moles of solute per liter of solution, mol/L, and has the abbreviation M.

dtimiraos/Getty Images

Introduction

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8 • Mixtures, Solution Concentrations, Osmosis, and Dialysis

8.4 Solution Dosage Calculations in Medicine • A flow rate is the solution

volume per unit time that a solution is administered into a vein by IV.

Catherine Bausinger

8.5 Solution Dilution Calculations • Solutions can be prepared

C1 3 V1 5 C2 3 V2 from more concentrated solutions, a process known as dilution.

• The dilution equation C1V1 5 C2V2 can be solved

for any variable, provided the other three variables are given.

8.6 Osmosis and Dialysis • The cell membrane is a selectively

permeable membrane, allowing water and certain solutes to cross the membrane. Colloids and larger

David M. Phillips/ Science Source

particles cannot cross a selectively permeable membrane. • Substances with a smaller size, neutral charge, and which are less polar are better able to cross the cell membrane. • Osmosis is the diffusion of water across a selectively permeable membrane from the less concentrated solution to the more concentrated solution. The volume of the more concentrated solution increases as a result. • Osmotic pressure is the external pressure that must be applied to the more concentrated solution to prevent osmosis. Reverse osmosis occurs when an external pressure greater than the osmotic pressure is applied, causing water to diffuse against the concentration gradient. • IV solutions must be isotonic with red blood cells to maintain the normal volume of the cell. In a hypotonic solution, water enters the cell, causing hemolysis. In a hypertonic solution, water diffuses out of the cell, causing crenation. • Dialysis is the diffusion of small solute particles through a dialysis membrane. Solutes diffuse from the hypertonic to the hypotonic solution until both solutions are isotonic.

key Words Aggregates many small molecules or ions clumped together that often form the large particles of a suspension. Aqueous solution A homogeneous mixture in which water is the solvent. Blood plasma Whole blood that has had the blood cells removed, typically through centrifugation. Blood serum Blood plasma that has had the fibrinogen and other clotting factors (proteins) removed. Cell membrane The selectively permeable barrier that separates the aqueous mixture inside the cell from the aqueous mixture outside the cell, and controlling what substances enter and leave the cell. Colloid A particle with a diameter between 1 nm and 1,000 nm dispersed in a medium. Colloids include large biomolecules such as proteins and polysaccharides. Colloidal dispersion A homogeneous mixture containing colloids evenly distributed throughout the medium. Colloidal dispersions have an opaque appearance. Concentration A quantitative measure of the amount of solute per total solution 1solute 1 solvent2. Some common concentration units are mg/dL, % m/v, and moles/L (M).

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Concentration gradient A solution with a higher concentration in contact with a solution with a lower concentration often separated by a membrane. Crenation The shrinkage of red blood cells that occurs when they are immersed in a hypertonic solution, due to water diffusing out of the cell through osmosis. Dialysis Diffusion of small ions and molecules from a hypertonic solution to a hypotonic solution across a dialysis membrane. Diffusion The movement of particles through a solvent as a result of their kinetic energy. Dilute A solution with a relatively small amount of solute dissolved in the solvent. Dilution The process of preparing a more dilute solution from a more concentrated solution. Electrolyte An aqueous solution containing dissolved ions. The solution can conduct electricity because there are charged ions in solution that complete the electrical circuit. Flow rate A volume of solution per unit time. It is the rate in which an IV solution is delivered to a patient. Hemodialysis A life-support treatment that performs the function of the kidneys and is based on the chemical principles of dialysis.

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Hemolysis The swelling and bursting of red blood cells when immersed in a hypotonic solution, which occurs as a result of water diffusing into the cell through osmosis. Heterogeneous mixture A mixture whose components are unevenly distributed throughout the mixture, such as a suspension. Homogeneous mixture A mixture whose components are evenly distributed throughout the mixture; such as solutions and colloidal dispersions. Hydration The process of solvation where water is the solvent. Hydrophilic A molecule or part of a molecule that is attracted to water because it is polar. Hydrophobic A molecule or part of a molecule that is nonpolar, and therefore, avoids water. Hydrophobic effect The tendency for a nonpolar liquid and a polar liquid not to mix because it would disrupt hydrogen bonding in the polar liquid. Hypertonic solution The more concentrated solution. Hypotonic solution The less concentrated solution. Immiscible Two mutually insoluble liquids that form separate layers, like oil and vinegar. Intravenous (IV) The administration of a solution through a vein. Ion-dipole interactions The force of attraction between an ion and the opposite partial charges on several polar molecules, such as water. Isotonic solutions Solutions that have the same concentrations. Medium The component of a colloidal dispersion and a suspension that is present in the greater quantity. Analogous to the solvent in a solution. Mixture A combination of two or more elements and/or compounds in any proportion. Molar concentration A unit of concentration represented by the moles of solute per liter of solution: mol/L, abbreviated M. Also referred to as molarity. Molarity See molar concentration. Nonelectrolyte A solution composed of neutral solute molecules or an insoluble ionic solid; the solution does not conduct electricity because there are no charged particles in solution. Osmolarity The molar concentration of all the particles in a solution that contribute to its osmotic pressure.

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Osmosis Simple diffusion of water across a selectively permeable membrane from the hypotonic to the hypertonic solution. Osmotic pressure The minimum amount of pressure that must be applied to the hypertonic solution to prevent osmosis. Reverse osmosis The application of a pressure greater than the osmotic pressure to the hypertonic solution, so that water diffuses against the concentration gradient. It crosses a selectively permeable membrane from the hypertonic to the hypotonic solution. Saturated solution A solution with the maximum amount of solute that will dissolve in the solvent. Selectively permeable membrane A membrane that allows only certain molecules and ions to diffuse across the membrane. Simple diffusion The spontaneous movement of molecules or ions from a region of higher concentration to a region of lower concentration. Solute Particles less than 1 nm in diameter dissolved in a solvent. Solution A homogeneous mixture that contains one or more solutes dissolved in the solvent. Solvation The process of dissolving. At the molecular level, compounds are surrounded by solvent molecules to form either ion-dipole interactions, in the case of ionic compounds, or intermolecular forces of attraction with solvent molecules, in the case of molecular compounds. Solvent The component in a solution that is present in the greatest amount and dissolves the solute(s). Water is the solvent in an aqueous solution. Stock solution A concentrated solution with a known concentration from which less concentrated (dilute) solutions can be prepared. Supersaturated solution A solution that contains more than the maximum amount of solute that is soluble in solution, and usually forms a precipitate. Suspension A heterogeneous mixture containing particles larger than 1,000 mm (1 micrometer) in size, which are unevenly distributed throughout the medium and will eventually settle if no mixing occurs. Volumetric flask A special type of glassware with a precise volume marking on the neck that is used to measure the correct volume of solution when preparing a solution with a given concentration.

Additional Exercises Kidney Disease 40 41 42 43 44

When kidney disease destroys the kidneys, what options does the patient have? When kidney disease destroys the kidneys, what is the procedure that can perform the function of the kidneys for a period of time? What is a mixture? Is blood a mixture? What are some components of blood?` What function do the kidneys perform in the body? What is the renal artery?

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45 46 47 48 49 50

How do the kidneys remove waste produced by cells? Do the kidneys remove proteins from the blood? What structures allow the kidneys to filter the blood? What happens to the waste, toxins, and surplus water that the kidneys have filtered out of the blood? What are some indications of kidney failure (renal failure)? If a doctor tested a patient’s urine for renal failure, what would the doctor look for?

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8.1 Types of Mixtures 51 52

53 54

55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74

What is the difference between a mixture and a pure substance? Indicate whether the following statements are TRUE or FALSE. a. Mixtures cannot be separated into their individual components through physical means. b. Mixtures contain only one component. c. Mixtures can differ in the relative amount of each component. d. A solution is a type of mixture. e. Solutions are always composed of a solid solute in a liquid solvent. What is the difference between a heterogeneous mixture and a homogeneous mixture? Classify the following mixtures as heterogeneous or homogeneous. a. tomato juice b. a cup of tea with honey c. a bowl of chicken noodle soup d. urine e. gasoline f. blood g. Pepto-Bismol What are the two types of homogeneous mixtures? What is a suspension? What is the major component of an aqueous mixture? What is the abbreviation for an aqueous mixture? Which of the following types of mixtures has particles with the largest size: solutions, colloidal dispersions, or suspensions? Which of the following types of mixtures has particles ranging in size from 1 nm to 1 mm: solutions, colloidal dispersions, or suspensions? What is the major component of a solution called? What is the major component of a colloidal dispersion called? Approximately how large are the solute particles in an aqueous IV solution containing sodium chloride? What are the two components called that make up a solution? Which component of a solution is present in the greater amount? What are the components of a colloidal dispersion called? Which of the components of a colloidal dispersion is present in the smaller amount? Is an aqueous solution transparent or opaque? Is a colloidal dispersion transparent or opaque? What piece of laboratory equipment can be used to separate the large particles from the medium in a suspension? When a test tube of whole blood is centrifuged, is blood plasma at the top or the bottom of the test tube? Why are some medications prepared as suspensions? Is dry air a solution, a colloidal dispersion, or a suspension? Are mixtures containing only gases classified as solutions, colloidal dispersions, or suspensions?

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75 76

78 79

80 81

Explain why dental amalgam is classified as a solution. What is the solvent in dental amalgam? Identify the solute and the solvent in each solution below. a. an IV solution of aqueous glucose b. a dental amalgam of mercury and silver c. an IV solution of aqueous MgSO4, used to prevent seizures in pregnant women with preeclampsia Identify one solute and the solvent in each solution below. For a., b., and c., consult Table 8-2. a. bronze b. lemon-lime soda c. 3 mL of isopropyl alcohol dissolved in 20 mL of an aqueous solution d. dry air Humid air is a solution of liquid water in air. Identify the solutes and the solvent and their states of matter. Smoke from a fire is a solution of particulate matter, soot (carbon), and gases such as carbon monoxide and carbon dioxide in air. Identify the solutes and the solvent and their states of matter. A bottle of rubbing alcohol is a solution of 2-propanol (a liquid) and water. Identify the solute and solvent and their states of matter. What is a solute and the solvent in seawater? What is the state of matter of this solute and solvent?

8.2 Solutions: Dissolving Covalent and Ionic Compounds in a Solvent 82 83 84 85 86

What is the difference between hydration and solvation? Explain the statement “like dissolves like.” Is a polar substance soluble in a polar or a nonpolar solvent? Is a nonpolar substance soluble in a polar or a nonpolar solvent? Identify each of the solvents below as polar or nonpolar. a. CCl4,

Cl C

Cl H

b. 2-propanol,

c. acetic acid,

d. carbon dioxide, O

e. octane, H H

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Additional Exercises

f. methanol,

H C

H 87

Consider what happens when ethanol, is dissolved in water. what hydrogen bonds are broken and what new hydrogen bonds are formed?

H 88 89 90 91 92

H H What does the term immiscible mean? Are two polar liquids immiscible? Explain the hydrophobic effect? Does the hydrophobic effect occur between a nonpolar liquid and water, or between a polar liquid and water? When a liquid hydrocarbon is mixed with water, two layers are formed? Explain why this occurs. Which of the following compounds will dissolve in water? Explain your answer. a. hexane, C6H12 b. H O H C

c. methanol,

H H

H d. decane, C10H22 e. 1-propanol, H

Which of the following compounds will dissolve in pentane 1C5H12 2? Explain your answer. a. hexane, C6H12 b. H O H C

c. CH3OH d. H H

e. tetrachloroethene, Cl

Cl C

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C Cl

94 Based on your everyday experiences, which of the following household substances will dissolve in water? a. sand b. butter c. waterproof mascara d. regular mascara e. baking soda, NaHCO3 95 Explain what happens on the molecular level when sugar is dissolved in black coffee. What intermolecular forces of attraction are involved? Are any covalent bonds in the sugar molecules broken? 96 You can make rock candy by dissolving sugar in warm water until no more sugar dissolves. At this point, what type of solution do you have? If you continue to add sugar, what type of solution do you have? 97 Although sodium chloride is soluble in water, why does a precipitate eventually form if you keep adding sodium chloride to water? Explain what occurs on the molecular level. 98 Supersaturated solutions of sodium acetate have been used as reusable hot packs. Before the hot pack is activated, the solution is clear with a metal disk inside. To activate the hot pack, the metal disk is clicked, which releases a crystal of sodium acetate. Sodium acetate then precipitates out of solution, an exothermic process, causing the pack to become hot. Explain on a molecular level why the precipitate forms. H O

–

O Na

H 99 What causes kidney stones? 100 Children’s acetaminophen is sold as an oral suspension. If it sits in the medicine cabinet for awhile, what forms at the bottom of the bottle? Why do you need to shake the bottle before administering the medicine? 101 What is an ion-dipole interaction? 102 Which of the following form ion-dipole interactions? a. NaCl and water b. methanol and water c. sodium hydrogen phosphate, Na2HPO4, and water d. hexane and water 103 Many athletes add Epsom salt 1MgSO4 2 to the bath water to soothe their sore muscles. On the molecular level, explain what happens when MgSO4 is added to water. What forces of attraction are involved? What types of bonds are broken in the process? 104 Ethanol and KCl both dissolve in water. What happens to the ionic bonds when KCl dissolves in water? What types of interactions form between the ions of KCl and water, allowing KCl to dissolve? What happens to the covalent bonds in ethanol when it dissolves? What types of intermolecular forces of

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attraction occur between ethanol and water that allow ethanol to dissolve? 105 Write equations to describe what happens when the following soluble ionic compounds dissolve in water. a. MgSO4 c. KCl b. Na3PO4 d. Na2CO3 106 Write equations to describe what happens when the following soluble compounds dissolve in water. a. CaCl2 c. K3PO4 b. NH4Cl d. NaCl 107 When dissolved in water, which of the following compounds is an electrolyte? a. glucose b. NaCl c. K3PO4 d. ethanol,

H H 108 Which of the following compounds is an electrolyte? a. Li3PO4 c. sucrose, table sugar, a molecule b. MgCl2 d. sodium hydroxide 109 Which of the following compounds is a nonelectrolyte? a. acetic acid, CH3CO2H b. KCl c. methanol, CH3OH d. Mg1OH2 2 110 Which of the following compounds is a nonelectrolyte? a. Ca1OH2 2 b. glucose, (C6H12O6) c. Na3PO4 H H H d. H

H H H 111 Explain why barium sulfate, BaSO4, forms a suspension in water rather than dissolving in water, even though it is an ionic compound. 112 Indicate whether the following statements are TRUE or FALSE. a. When a molecule dissolves in water, the covalent bonds of the molecule break. b. Hydrogen bonding occurs when polar molecules are dissolved in water. c. Solutions containing charged ions in solution conduct electricity.

8.3 Solution Concentration 113 Which solution is more dilute: a solution with 5 g of NaCl and 100 mL of water or a solution with 30 g of NaCl and 100 mL of water? 114 Which solution has the higher concentration: a solution with 80 g of sugar in 100 mL of water or a solution with 25 g of sugar in 100 mL of water?

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115 Solute concentration is a ratio between _____________________ and _____________________. 116 How is a volumetric flask used to prepare a solution with a known concentration? 117 Should you use a beaker to measure the volume of a solution with a given concentration? 118 How would you prepare a solution with a given concentration? 119 The concentration of an intravenous (IV) vancomycin solution, used to treat bacterial infections, contains 500. mg vancomycin in 100. mL of total solution. What is the m/v concentration of this solution in milligrams per milliliter (mg/mL)? 120 The concentration of an intravenous (IV) vincristine sulfate solution, a chemotherapy agent used to treat acute leukemia, contains 1 mg vincristine sulfate in 1 mL of total solution. What is the m/v concentration of this solution in milligrams per milliliter (mg/mL)? 121 How many grams of glucose would be required to prepare 5.0 mL of a glucose solution that has a concentration of 78 mg/dL? 122 A patient’s blood test shows that her hemoglobin concentration is 14 g/dL. How many milligrams of hemoglobin are in every 2.5 mL of the patient’s blood? 123 Ampicillin is an antibiotic that can be administered intravenously. It is sold in vials that contain 2.0 g of ampicillin. Sterile water is added to the vial to make a solution that has a concentration of 250. mg/mL. What is the total volume of the solution after the water has been added? 124 An EpiPen Jr., used to treat anaphylactic allergic reactions, contains 0.15 mg of epinephrine. The concentration of epinephrine in each syringe is 0.50 mg/mL. What is the volume of solution in each syringe? 125 A solution is prepared by dissolving 8.5 g of dextrose in enough water to produce a total solution volume of 300. mL. What is the concentration of this solution in % m/v? 126 A 10. mL sample of whole milk contains 0.58 g of casein, a protein. What is the concentration of casein in this sample of milk in % m/v? 127 You are asked to prepare 1.0 L of a 3.3% dextrose solution for IV therapy. How much dextrose do you need to weigh out to prepare this solution? 128 How many grams of sodium chloride would you need to prepare 500. mL of a 0.90% normal saline solution for IV therapy? 129 How many grams of sodium chloride is in 250 mL of a 0.90% saline solution used for IV therapy? 130 How many milliliters of total solution can be prepared from 36.0 g of dextrose if you prepare a 3.3% dextrose solution for IV therapy? 131 How many liters of a 0.90% normal saline solution for IV therapy can be prepared from 45 grams of sodium chloride? 132 How many milliliters of a 0.90% saline solution for IV therapy can be prepared from 27.5 grams of sodium chloride?

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133 According to the EPA, the maximum allowable amount of cadmium in drinking water is 5 ppb. Express this concentration in g/mL, % m/v, and ppm. 134 According to the EPA, the maximum allowable amount of glyphosate in drinking water is 0.000 000 7 g/mL. Glyphosate is a compound found in the runoff from herbicide use. Express this concentration in % m/v, ppm, and ppb. 135 The maximum acceptable level of arsenic, (As) in water is 0.05 ppm. At that level, how many grams of arsenic would there be in 1 L of water? 136 In New Zealand, the legal blood alcohol limit is 400 mg of alcohol per 1 L of breath. What is this alcohol concentration in parts per billion, ppb? 137 What is the molar concentration of a solution that has 0.36 mol of dextrose in 250 mL of solution? 138 What is the molarity of a solution that has 0.24 mol of glucose in 185 mL of solution? 139 A patient’s blood test shows that he has a bilirubin level of 0.012 mol/L. How many moles of bilirubin are in 5.0 mL of his blood? 140 A patient’s blood test shows that she has elevated levels of LDL (low-density lipoproteins) at 4.14 mM. How many moles of LDL are in 8.00 mL of her blood? 141 What is the volume of a 2.2 M solution containing 0.036 mol of NaCl? 142 What is the volume of a 0.56 M solution containing 2.5 mol of glucose?

8.4 Solution Dosage Calculations in Medicine 143 An order is given for 50. mg of Vistaril, an antihistamine, to be administered every 3 hr. The suspension has a concentration of 25 mg/5.0 mL. What volume, in milliliters, of the suspension should be administered to the patient every 3 hr? 144 An order is given to administer 187.5 mg of BetapenVK, an oral formulation of penicillin. The suspension contains 125 mg of Betapen-VK in 5.0 mL of solution. What dose, in milliliters, of the oral formulation should be administered to the patient? 145 An order is given to administer 15 g of lactulose, often used for treating complications of liver disease. The lactulose syrup has a concentration of 10. g/15 mL. What volume, in milliliters, of syrup should be given to the patient? 146 An order is given to administer methylprednisolone, an anti-inflammatory drug, by IV at a rate of 40. mg every 30 min. The IV bag contains 125 mg of methylprednisolone in every 2 mL of solution. What should the flow rate be in milliliters per minute? 147 Morphine is a potent painkiller that acts directly on the central nervous system to relieve pain. An order is given to administer 2.0 mg of morphine to a patient as needed for breakthrough pain. The solution supplied contains 2.0 mg/mL of morphine. If 2.0 mg of morphine should be administered over a period of 5 min, what should the flow rate be in milliliters per minute? 148 Nipride is often ordered for patients who have experienced severe heart failure. A patient is

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receiving a Nipride solution by IV at a rate of 60. mL/hr. The concentration of the Nipride solution is 50. mg/250 mL D5W. How many milligrams of Nipride per hour is the patient receiving? 149 Aminophylline is used in the treatment of bronchial asthma. A patient is receiving an aminophylline solution by IV at a rate of 22 mL/hr. The concentration of the solution is 2.0 g/1.0 L D5W. How many grams per hour of aminophylline is the patient receiving? 150 Nitroglycerine, used to treat patients with angina, is prescribed for a patient by IV at a rate of 225 mg>min. The IV bag contains 50. mg nitroglycerine/250 mL D5W. How many milliliters per hour should the patient receive?

8.5 Solution Dilution Calculations 151 A student needs to prepare 100. mL of a 0.50 M NaOH solution from a 2.0 M NaOH stock solution. How should she prepare this solution? 152 A student transferred 30. mL of a 4.5 M HCl stock solution to a 250. mL volumetric flask and then added water to the mark on the volumetric flask. What is the molar concentration, M, of the dilute solution? 153 How would you prepare 100. mL of a 0.45% halfnormal saline solution from a stock solution of 0.90% normal saline solution? 154 What is the concentration of a dextrose solution prepared by diluting 15 mL of a 2.0 M dextrose solution to 25 mL using a 25 mL volumetric flask?

8.6 Osmosis and Dialysis 155 What does permeability in a selectively permeable membrane mean? 156 What types of substances can cross the selectively permeable cell membrane? 157 What types of substances cannot cross the selectively permeable cell membrane? 158 What does the term diffusion mean? 159 What is a concentration gradient? 160 What factors determine whether or not a solute can diffuse across a cell membrane? 161 What types of compounds have the greatest ability to diffuse across the cell membrane? 162 What types of compounds require assistance (energy and specialized proteins) to cross the cell membrane? 163 Why are ions not able to cross the cell membrane? 164 Which ion or molecule in each pair below is better able to diffuse across a cell membrane, and why? a. glycerol, or sodium ion, Na1 H

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165

166 167 168 169 170 171 172

8 â&#x20AC;˘ Mixtures, Solution Concentrations, Osmosis, and Dialysis b. carbon dioxide, or a small neutral polar molecule like an amino acid c. a protein, or a neutral amino acid d. potassium ion, K1, or nitrogen, N2 Which ion or molecule in each pair below is better able to cross a cell membrane, and why? a. glucose, or a complex carbohydrate like starch b. a neutral amino acid, or chloride ion, Cl 2 c. potassium ion, or water d. oxygen, or water What is osmosis? Does the volume of the hypertonic solution increase or decrease as result of osmosis? What is osmotic pressure? During reverse osmosis, does water diffuse across the membrane to the hypertonic solution, or does it diffuse to the hypotonic solution? What is the difference between hypertonic, hypotonic, and isotonic solutions? In reverse osmosis, is the pressure applied to the hypertonic solution greater than or less than the osmotic pressure? Explain. Consider the solutions shown below separated by a selectively permeable membrane. Indicate the direction that water diffuses between solution A and solution B, or if it does not. Which solution will see an increase inSelectively volume?permeable membrane Selectively permeable membrane (a) Solution A Solution B Selectively membrane (a) Solution A permeableSolution B (a) Solution A Solution B

Solution A is 0.25 M NaCl. Solution A is 0.25 M NaCl. Solution B is 0.05 M NaCl. Solution A 0.25 M NaCl. B is 0.05 Solution B is 0.05 M NaCl. (b) (b)

Solution A Solution A

Solution B Solution B

(b)

Solution A

Solution B

Solution A is 0.02 M sucrose. Solution A is 0.02 M sucrose. Solution B is 0.02 M glucose Solution 0.02 M glucose sucrose. BMissucrose. and 0.01A and 0.01 M sucrose. Solution B is 0.02 M glucose and 0.01 M sucrose. (c) (c)

Solution A Solution A

Solution B Solution B

(c)

Solution A

Solution B

Solution A is 0.02 M sucrose. Solution A is 0.02 M sucrose. Solution B is 0.02 M glucose. A is 0.02 M glucose. sucrose. Solution B

173 What happens if you apply pressure to seawater separated from fresh water by a selectively permeable membrane? What is this process called? If pressure is not applied, what occurs as a result of osmosis? 174 What does the term osmolarity mean? 175 Preeclampsia is a condition that occurs in some women during pregnancy. The main symptoms are high blood pressure and protein in the urine; however, if not treated, it can cause seizures, stroke, or liver rupture in the mother. The only treatment for this condition is to deliver the baby. Pregnant women who have preeclampsia are at an increased risk of hemolysis of their red blood cells. What is hemolysis of red blood cells? 176 A blood smear, a technique where a thin film of blood is examined under a microscope, is used to diagnose sickle cell anemia. Some of the staining techniques used to visualize the blood cells involve hypertonic solutions which cause crenation of the red blood cells. What happens to the red blood cells? 177 In which direction does water diffuse across a membrane during osmosis between a hypertonic and a hypotonic solution separated by a selectively permeable membrane? 178 What is dialysis? 179 What is the difference between osmosis and dialysis? 180 When dialysis occurs, why do colloidal particles not cross the selectively permeable membrane but some solute particles do? 181 If two solutions on either side of a selectively permeable membrane are isotonic, do you expect dialysis to occur? Explain your answer. 182 Two compartments are separated by a selectively permeable dialysis membrane as shown below. a solution of creatine (a small molecule) and globulin (a type of large protein molecule) are in one compartment, and pure water is in the other compartment. Describe how you could separate creatine from globulin by dialysis. Selectively permeable membrane Solution A

Pure water

Solution A is an aqueous mixture of creatine ( ) and globulin ( ). Solution B is pure water.

Chemistry in Medicine: Hemodialysisâ&#x20AC;&#x201D;Performing the Function of the Kidneys 183 A patient has a sudden onset of renal failure. Does the patient have acute or chronic renal failure? 184 What can cause acute renal failure? 185 What can cause chronic renal failure? 186 Why does a patient with less than 15% kidney function require hemodialysis? 187 What is the function of the dialyzer in hemodialysis?

Solution B is 0.02 M glucose.

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Answers to pr actice e xercises

188 Is the dialysate isotonic, hypotonic, or hypertonic compared to the patient’s blood? 189 What substances are removed from a patient’s blood during hemodialysis? 190 In hemodialysis, why does the pressure in the dialyzer need to be higher than the osmotic pressure of the patient’s blood?

Challenge Questions 191 Identify the following as either a colloidal dispersion or a solution. a. a glass of milk b. a glass of lemonade c. whipped cream d. marshmallows e. a glass of wine f. a spoonful of mayonnaise 192 Identify the following as either a solution or a colloidal dispersion. a. 5% dextrose b. Jell-O c. blood d. smoggy air e. mercury amalgam used in dentistry f. butter cookies 193 Why are mixtures of proteins or starch in water classified as colloidal dispersions?

194 Use the hydrophobic effect to explain why water will bead-up on a vinyl tablecloth. Note that vinyl is a hydrocarbon. 195 Would turpentine, C10H16, be soluble in water or hexane? 196 Calculate the molarity of a normal saline solution (0.90% NaCl). The molar mass of NaCl is 58.44 g/mol. 197 What is the % m/v of a 0.025 M solution of dextrose? The molar mass of dextrose is 180.156 g/mol. 198 Two aqueous solutions are separated by a selectively permeable membrane. Solution A contains 0.62 mol of NaCl in 235 mL of aqueous solution, and solution B contains 0.45 mol of NaCl in 156 mL of aqueous solution. Will water flow from compartment A to B, or vice versa? Hint: You will first have to calculate the molar concentration of each solution. 199 Two aqueous solutions are separated by a selectively permeable membrane. Solution A contains 15 g of dextrose in 458 mL of aqueous solution, and solution B contains 43 g of dextrose in 325 mL of aqueous solution. Will water flow from compartment A to B, or vice versa? Hint: First calculate the % m/v of each solution.

Answers to Practice Exercises 1 2

3 4

6 7

a. heterogeneous b. heterogeneous c. homogeneous d. homogeneous The solute particles in a solution are smaller than 1 nm. Colloids range in size from 1 nm to 1 mm 11,000 nm2. The particles of a suspension are larger than 1 mm 11,000 nm2. a. a solution b. a suspension c. a solution d. a colloidal dispersion a. solute: ethanol; solvent: water b. solutes: NaCl and sugar; solvent: water c. solute: CO2; solvent: O2 “Like dissolves like” means that polar solvents dissolve polar solutes, and nonpolar solvents dissolve nonpolar solutes. The “like” property is polarity. Sugar is ‘like’ water in that it is also polar and can form hydrogen bonds to water. Kidney stones form when supersaturated solutions of calcium salts form in the kidneys. A supersaturated solution often contains a precipitate, or suspended particles, whereas a saturated solution is homogeneous and transparent. The amount of solute in a supersaturated solution exceeds the number of solvent molecules available to dissolve the solute at that temperature, whereas a saturated solution has the maximum amount of solute that can be dissolved in that amount of solvent.

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8 a. does not dissolve, because NaCl is an ionic compound, and hexane is a nonpolar solvent b. yes, dissolves because CCl4 is a nonpolar compound, and hexane is a nonpolar solvent c. does not dissolve, because methanol is polar and hexane is nonpolar d. yes, dissolves because pentane and hexane are both nonpolar compounds H

O H O

H O H

N H

H N H

O H

a. soluble in water because NaCl is an ionic compound, and therefore, Na1 and Cl 2 form iondipole interactions with water b. insoluble in water because CCl4 is a nonpolar compound (C i Cl bond dipoles cancel), whereas water is a polar solvent c. insoluble in water because gasoline is a mixture of hydrocarbons and hydrocarbons are nonpolar, whereas water is polar

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8 • Mixtures, Solution Concentrations, Osmosis, and Dialysis

d. soluble in water because methanol and water are polar. Methanol is polar because it has an O i H bond and only one carbon.

e. soluble in water because acetic acid is polar, due to the O i H bond and few carbon atoms in the molecule

f. soluble in water because it is an ionic compound 11

13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

that forms ion-dipole interactions with water: Na1 1aq2 and PO432 1aq2 a. MgCl2 1s2 h Mg21 1aq2 1 2 Cl 2 1aq2 b. K3PO4 1s2 h 3 K1 1aq2 1 PO432 1aq2 c. NaHCO3 1s2 h Na1 1aq2 1 HCO23 1aq2 a. nonelectrolyte; because it is a covalent compound b. electrolyte; because it is a soluble ionic compound c. nonelectrolyte; because it is a covalent compound d. electrolyte; because it is a soluble ionic compound 0.008 mg/mL 400 mg/dL 35 mg of glucose 0.23 dL 6.25 mL of lidocaine solution 8.9% (m/v) sucrose 278 mL of 0.900% saline solution 4.5 g of NaCl b. (most concentrated) 7 a. 7 d. 7 c. (least concentrated) 7.7 3 1023 M or 0.0077 M 3.0 mol of Li 1 ions 0.4 L of solution administer 1.5 mL of the Tylenol solution every 4 hrs administer 12.5 mL of the Tegretol solution as needed administer 10 mL of the Atarax solution every 4 hrs 16 mL/min. 0.037 mL/hr 10 units/hr

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31 32 33 34 35 36 37

25 mL of the aqueous 2.0 M solution 0.5% 0.80 M Proteins are very large molecules, which cannot cross the selectively permeable cell membrane. a. the amino acid, because it is neutral b. water, because it small and neutral, whereas Na1 is small but has a charge c. carbon dioxide, because it is neutral and nonpolar, whereas K1 has a charge d. glucose, because it is a much smaller molecule than starch a. i. Solution A is hypertonic; solution B is hypotonic ii. Water diffuses from solution B to solution A iii. The volume of solution A will increase. b. i. Solution A is hypertonic; solution B is hypotonic ii. Water diffuses from solution B to solution A iii. The volume of solution A will increase. c. i. Solution A is hypotonic; solution B is hypertonic ii. Water diffuses from solution A to solution B iii. The volume of solution B increases. d. i. Solutions A and B are isotonic ii. There is no net diffusion of water iii. The volume of both solutions remains the same. Since a 1.5% m/v saline solution is hypertonic relative to a red blood cell (0.90%), water will diffuse out of the red blood cell through osmosis, resulting in crenation. Water flows from the more concentrated solution to the less concentrated solution, against the concentration gradient, which is the reverse direction of osmosis. The 0.90% solution is hypertonic. The 0.45% solution is hypotonic. Dialysis will cause ions to diffuse from the 0.90% solution to the 0.45% solution until the concentration on both sides of the membrane is equal.

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