Muestra del libro Physics and Chemistry 2º ESO Proyecto 5 etapas

Rafael Jiménez Prieto Pastora M.ª Torres Verdugo

Classification of matter. Mixtures and solutions

Salterns along the coast of Andalusia e e e

Salt has been one of the most widely used chemical compounds by humans since ancient times. Extracted from minerals or salt water, it has always been a precious commodity, bringing wealth to many coastal areas.

Form groups of three of four. By following instructions from your teacher and based on your answers to the questions below, you will discover more about salt extraction in Andalusia today.

Explore

1 Salterns are easy to spot in many coastal regions. What do these installations, which are often very old, consist of? Look for information in books or on the Internet and explain the principle on which they are based and how they work.

2 Andalusia, with its long coastline, has been home to salterns for many centuries. There are also salterns inland. Find out some information about the famous saltern of La Malahá, which has been operating for centuries.

3 The coast of Cádiz is ideal for extracting salt. In which towns in the province of Cádiz are there working salterns? Find out some information and interesting facts about them.

4 How is sea salt produced in Andalusia? What is salt used for today? Look for information in journals or on the Internet.

Elaborate

1 You are going to prepare a presentation about salterns in Andalusia based on the information you have collected.

2 Make sure you include photos and interesting facts and you quote your sources.

Communicate

1 Now you are more informed, what do you think about the need to keep traditional activities like salt extraction alive? Would it be better to restore the coastline? Hold a class discussion.

Concentration in a solution

Solutions can have a variable composition. To express the amount of solute in a solution, we must use a specific quantity, which is concentration.

Mass concentration per unit of volume shows the ratio of dissolved solute, expressed in units of mass, relative to the volume of solution.

It is usually expressed in grams of solute to litre of solution:

Read and learn

Some students have prepared a salt-water solution in the school laboratory. They weighed out 11.25 g of salt and dissolved it in water. They then added water to make the final volume of the solution 1.5 litres.

What is the mass per volume concentration of this solution?

1. Before we start calculating, we will make a diagram with the information we have been given, checking they are expressed in the right units:

2. We will then write the formula we are going to use and calculate the concentration. Finally we will interpret the result:

The concentration is 7.5 g/L, therefore 7.5 g of salt (solute) are dissolved in every litre of this salt-water solution.

How can mixtures be separated?

The components of a mixture can be separated by physical means. The choice of process in each case will depend on the type of mixture and the physical state of the components.

Heterogeneous mixtures of liquids

The process used for this type of mixture is decantation. This consists of leaving the mixture to stand so that the immiscible liquids separate spontaneously. In the laboratory, a special piece of equipment called a separatory funnel is used. Decantation. Oil Water

Emulsions are heterogeneous mixtures of two liquids that do not dissolve in each other. Most sauces are emulsions: mayonnaise, tomato sauce...

11. To prepare a solution, 8.75 g of solute have been weighed and dissolved in water to give a final volume of 3.5 L. What is the concentration of this solution in g/L?

When diluting, adding more solvent to an already prepared solution, decreases the proportion of solute in the solution.

12. We dissolve 1.5 g of solute in an amount of water to prepare a solution with a final volume of 200 mL. Calculate the concentration expressed in g/L.

13. A soft drink manufacturer is preparing a sugar-water solution, by dissolving 1,440 kg of sugar in water, producing 18,000 litres of solution. Calculate the concentration expressed in g/L.

14. The label of a cough syrup shows it has 1.6 mg/mL of active ingredient. How should we interpret this information? Explain your answer.

15. Calculate the mass concentration per unit of volume for the following solutions. Express your answers in grams per litre and explain what the results mean:

of salt in 630 g of water or solution B prepared by dissolving 10 g of salt in 30 g of water? Calculate it and express the result in mass percent.

17. The item of laboratory equipment shown in this picture is used to separate mixtures.

a) What is it called? Which separation method is it used for?

b) Which type of mixtures is it used for? Give an example.

18. Look in your textbook or on the Internet to find out which separation method you would use in each case and explain your answer clearly. Also read the information about the mixture that is provided.

a) Water and lithium chloride. Lithium chloride is highly soluble in water.

b) Water and petrol. They are two immiscible liquids.

c) Water and sand.

d) Sand, gravel and iron filings.

Oil and water are two immiscible liquids.

16. There are many ways of expressing the concentration of a solution. One of them is mass percent of solute. Look for information and answer the following questions:

a) What does it mean if a salt-water solution has a mass concentration of 18 %?

b) If a sugar-water solution has been prepared by dissolving 30 g of sugar in 170 g of water, what will its concentration be in mass percent? Calculate it and explain what the result means.

c) Which of the following two salt-water solutions has the highest concentration: solution A prepared by dissolving 70 g

19. Copy the following sentences in your notebook. Then, listen and write the missing words.

a) The of a solution tells us the ratio of solute to solvent.

b) If we increase the amount of solvent in a solution, we find its  concentration.

c) One way of expressing the concentration of a solution is in  per 

d) processes can be used to find the components of a mixture.

e) To separate two immiscible liquids, a process called  is used.

Heterogeneous solid-liquid mixtures

One of the most commonly used processes to separate heterogeneous mixtures in the laboratory and in everyday life is filtration.

This method is used to separate a heterogenous solidliquid or solid mixture.

Another method used to separate a heterogenous solidliquid mixture is centrifugation, which rotates the mixture at high speed.

This causes the solid to settle to the bottom.

Separating homogeneous mixtures

Crystallisation and distillation are the processes mostly used for this type of mixture.

Crystallisation separates a solid from a liquid in a homogeneous mixture, by evaporating the liquid. The liquid solvent evaporates slowly and the solid remains behind in the form of crystals.

Distillation is used to separate a homogeneous mixture of two liquids with different boiling points. A distillation flask is used, and the mixture is heated until the liquid with the lowest boiling point evaporates.

Stand Condenser

Cold water

What are separation processes used for?

In the manufacturing industry and our everyday lives we often need to isolate a substance by separating it from others in a mixture. Some examples are:

➜ Water treatment and purification. At a water treatment plant, a number of filtration, decantation and disinfection processes separate unwanted substances from the water.

➜ Fractional distillation of oil. At a refinery, raw crude oil is transformed into products like fuel (gas, butane, gasoline, diesel, kerosene), solvents (petroleum ether, ligroin), paraffin or asphalt using a fractional distillation process.

➜ Separation methods in the home. As we go about our everyday lives we use some of the above separation methods, for example, filtration, which we often use in the kitchen. 4

Changes in matter. Chemical reactions

When does a chemical change take place?

During physical changes, the composition of the matter remains the same.

However, a chemical change or process is when substances combine with others to produce new substances.

These new substances that were not present before cause the composition of the matter to change.

Unexpected colour changes.

CHEMICAL PROCESSES

Precipitation of substances.

Sudden temperature changes. Gas release.

What are chemical reactions?

Chemical changes are usually called chemical reactions.

A chemical reaction is any process in which new substances are formed. The substances already present are called reactants and the new ones formed are called products.

A chemical equation is used to represent this type of process. It consists of writing the formulas of the reactants on the left, an arrow to show the direction in which the reaction moves and the formulas of the products on the right. The physical state of all of the substances is added in brackets.

How are chemical reactions classified?

At the sub-microscopic level

In a chemical reaction, the reactants interact with each other, bonds between atoms in the reactants are broken, and the atoms rearrange and form new bonds. The reactants disappear and new substances called products are formed.

At the sub-microscopic level, in a chemical reaction, the atoms in the substances rearrange themselves.

Chemical reactions are usually classified by the chemical process taking place.

➜ Formation reactions. Reactions in which a compound is formed from its constituent elements.

➜ Decomposition reactions. When a compound breaks down to form several elements or simpler compounds.

➜ Combustion reactions. In a combustion reaction, a fuel reacts with oxygen, forming carbon dioxide and water and releasing a large amount of heat. It is this heat that is useful to us, not the products of the reaction.

1. When a yellow liquid and a white liquid are mixed a blue solid is formed, which settles at the bottom of the beaker. Has a chemical change taken place? Explain your answer.

2. From what you have learnt, explain the difference between a physical process and a chemical process, including an example of each type.

3. Say whether the following processes or changes are physical or chemical and explain why.

a) Water boils when heated in a pan.

b) A tub of butter has been left open and has gone bad.

c) A new drug is produced in a laboratory.

d) Used oil is filtered before being stored.

4. During the combustion of methane gas (CH4), it combines with oxygen from the air and produces carbon dioxide and water. Write a chemical equation for this reaction, indicating the reactants and the products.

Combustion of gas.

5. Based on what happens at the sub-microscopic level in a chemical reaction, explain whether the following statements are true or false:

a) When a chemical reaction takes place, new atoms are formed which give the products.

b) When a chemical reaction takes place, the atoms do not change, but the compounds do.

c) In a chemical process, some bonds are broken and others are formed.

6. Answer the following questions about chemical reactions, giving an example:

a) What are the reactants?

b) What are the products of a chemical reaction?

c) What information does a chemical equation give us?

7. When we put a piece of iron (Fe) in an aqueous solution of hydrogen chloride (HCl), after a while we see gas bubbles, and iron dichloride (FeCl2), which remains in the aqueous solution, and hydrogen gas (H2) are formed.

a) Can we say a chemical reaction has taken place? Why?

b) If so, what would the chemical equation be? Write it.

8. Find and correct the mistake in the following statements:

a) A chemical reaction is a process in which some reactants are heated to form products.

b) In a chemical reaction, new elements are formed, which are called products.

c) There are few chemical changes because substances do not change easily, so most are physical changes.

9. Say which of the following is a formation reaction, which is a decomposition reaction and which is a combustion reaction:

a) A single substance forms several products.

b) One of the reactants is oxygen, and a large amount of energy is released.

c) A compound is formed from its elements.

10. Copy the following sentences in your notebook. Then, listen and write the missing words.

a) A chemical process is when the  of the matter changes.

b) The substances formed following a chemical change are the 

c) Chemical changes are also called 

d) During a chemical change, the atoms of the  to give the products.

e) In a  reaction, a compound is formed from its constituent elements.

Iron oxidation. Rusty anchor at the port of Algeciras (Cádiz).

How is a chemical equation balanced?

You have learnt that at the sub-microscopic level, in a chemical reaction the bonds between the atoms of the reactions break, the atoms rearrange and new bonds are formed, giving new products. We say that a chemical equation is balanced when the number of atoms of each type in the reactants and in the products is the same.

A chemical equation must be balanced for it to be useful. If it is not balanced, we need to balance it.

The procedure to balance a chemical equation is:

➜ We write the unbalanced equation.

➜ We count the atoms.

➜ We place coefficients to balance the number of atoms, counting again every time.

➜ When the number of each type of atom is the same in the reactants and in the products, the equation is properly balanced.

Read and learn

When hydrogen gas (H2) reacts with oxygen gas (O2), water vapour (H2O) is formed. Write and balance the chemical equation for this reaction and interpret the result.

We start by writing the unbalanced equation using the information given, placing the reactants and product accordingly. We also count the atoms, in this case of hydrogen and oxygen:

Hydrogen Oxygen Water H2

2 atoms of hydrogen (H)

2 atoms of oxygen (O)

2 atoms of hydrogen (H)

1 atom of oxygen (O)

We have made the number of atoms of oxygen the same, but not the number of atoms of hydrogen. We need to add another molecule of hydrogen, like so:

Hydrogen Oxygen Water

H2 (g ) + O2 (g )

2 atoms of hydrogen (H)

2 atoms of oxygen (O)

2 H2O (g)

2 · 2 = 4 atoms of hydrogen (H)

2 · 2 = 4 atoms of hydrogen (H)

We have made the number of atoms of oxygen the same, but not the number of atoms of hydrogen. We need to add another molecule of hydrogen, like so:

2 H2 (g) + O2 (g)

2 · 2 = 4 atoms of hydrogen (H)

2 atoms of oxygen (O)

2 H2O (g)

2 · 2 = 4 atoms of hydrogen (H)

2 · 1 = 2 atoms of oxygen (O)

The equation is now balanced. It tells us that two molecules of hydrogen react with one atom of oxygen, giving two molecules of water.

Motion. Uniform linear motion 6

1. To find out whether an object is in motion we must choose a reference point.

a) In physics, when do we say a body is moving?

b) Imagine a pen on a desk. Is it at rest or in motion? Explain your answer.

c) What do you think the expression ‘motion is relative’ means? Explain your answer.

d) Following this, could an object be at rest and in motion at the same time, based on the principles of physics?

2. Imagine you are travelling by car. Describe the points of reference you could choose for the following situations to be true:

a) You are at rest.

b) You are far away from the point of reference.

c) You are just passing the point of reference.

3. Analyse each of the following situations and say whether they are at rest or in motion, giving reasons for your answer:

a) A bird is perched on a tree branch.

b) A boy is swinging on a swing.

c) Some friends are sailing on a lake.

d) A woman is driving her car.

4. Briefly answer the following questions:

a) What do we understand by linear motion?

b) What is the difference between uniform and non-uniform motion?

Curvilinear motion.

5. Classify the following motions using the following terms: linear/curvilinear/uniform/non-uniform.

a) A bus brakes when it approaches the bus stop.

b) Some children are riding on a rollercoaster.

c) A person is going up an escalator.

6. From the information given in the image, describe the position of the motorbike at each of the moments of time shown. Take the signpost as the point of reference.

5 m x

7. At an airport a plane is in position x1 = 230 m with respect to the control tower and the tanker is parked in position x2 = 580 m. How should we interpret this information? Draw a diagram to explain your answer.

8. What is displacement? And distance travelled? Describe a situation in which the displacement of the body and the distance travelled are different.

9. True or false? Explain your answer.

a) To calculate displacement we just need to know the position of the body.

b) As its name suggests, distance travelled is how far the body travels.

c) Displacement can never be equal to zero in motion.

10. From the information shown in the image, indicate the position at each moment of time and calculate the lorry’s displacement between two successive points. What is the total displacement?

11. Copy the following sentences in your notebook. Then, listen and write the missing words.

a) The  of  is an object or position used to determine the position of the body.

b) The  of a linear motion is a  

c) The  of the body is calculated as the distance from the point of reference in each  of time.

d) The difference between two positions of the body at different moments of time is the 

e) When we measure distance along the path, we get the   by the body.

What is uniform linear motion?

A suitcase is moving on a conveyor belt. Its path is a straight line and its instantaneous velocity is always the same. As you have learned, this simple motion must be classified as uniform linear motion.

An object or body is in uniform linear motion when its path is a straight line and its velocity is constant.

In uniform linear motion, because velocity is constant, the average velocity we calculate for any interval of time is equal to the instantaneous velocity at any given moment.

Uniform motion graphs

In uniform linear motion, there is a linear relationship between position and time. In other words, if we draw a graph and put time on the x axis and position on the y axis, we would get a straight line. The velocity graph would also be a straight line because it is constant.

What is non-uniform motion?

If an object’s velocity increases or decreases over time it has non-uniform motion. This is the case of applying brakes or free-fall. A new quantity is used to measure changes in velocity, called acceleration.

The average acceleration (aav) of an object is the change in velocity divided by the change in time. The SI unit used to measure acceleration is metres per second squared (m/s2).

Commercial aircrafts. These aircrafts perform a uniform linear motion for a large part of their flight path.

21. Say which of the following are examples of linear and uniform motion. Explain your answer.

a) A car moves along a straight line and the speedometer reads 100 km/h all of the time.

b) A ball rolls round a circular track, making two revolutions per minute.

c) A cyclist sprints to cross the finishing line.

22. A motorbike is riding along a long stretch of a dual carriageway. In five seconds it travels 140 m and in the next seven seconds it travels 196 m. Based on this information, does it have uniform linear motion? Explain why/why not.

23. A carton of juice is moving on a conveyor belt. Check whether its motion is uniform or not, calculating the average speed between moments 1 and 2, and comparing this velocity to the velocity calculated by taking moments 2 and 3.

26. An object starting from the point of reference moves in uniform motion and every 10 seconds it travels 15 m along the path. Based on this information:

a) Draw a table that shows the position of the object at moments t1 = 0 s, t2 = 10 s, t3 = 20 s, t4 = 30 s, t5 = 40 s and t6 = 50 s.

b) Draw the x-t graph of this motion and interpret it.

c) Based on the above information and bearing in mind the object is in uniform linear motion, what would the v-t graph look like? Why? Explain your answer.

24. Position-time (x-t) graphs of uniform motion are straight lines. Answer the following questions:

a) What is the slope on this type of graph?

b) What does the intercept mean?

c) How can we find out the position of the object for a given moment of time from the graph?

25. Look at these x-t graphs of three objects:

a) Are they uniform linear motion? Why?

b) Which object is moving faster, 1 or 2? Explain your answer.

c) Do any of them start to move from the point of reference? Explain your answer.

Braking. Velocity decreases, so it is non-uniform motion.

27. Explain in detail why the following motion is not uniform:

a) A swing swinging.

b) A car stopping at a red light.

c) A ripe apple falling from a tree.

d) Jumping on a trampoline.

28. At moment t1 = 30 s, the velocity of an object is 26 m/s. 20 seconds after this moment, its velocity is 14 m/s. What is the acceleration? Interpret the result.

29. Copy the following sentences in your notebook. Then, listen and write the missing words.

a) Motion in which  is constant is called 

b) The average  of an object that moves in uniform linear motion is the same as its  velocity.

c) The x-t graph of a uniform linear motion is a  

d) Free-fall is a non- motion, in other words, it is  motion.

e) Average  measures the change in velocity in an interval of time.

Copy the following sentences in your notebook. Then, write the missing words.

1. It is a type of matter formed by different components that can be visually distinguished and easily separated by physical means. A

2. This term refers to any homogeneous mixture where the components can be found in different states. A

3. It is a quantity to express the ratio of solute to solvent in a solution. The

4. It is the name given to a chemical change during which new substances are formed. A

5. It represents a chemical process, with the reactants on the left and the products on the right, separated by an arrow. A

6. It is a substance that is added to the reactants of a chemical reaction to increase the reaction rate without getting consumed in the process. A

7. It is the point we use to establish the position of an object at different moments of time to find out whether it is moving or not. The

8. It is the motion of an object that moves in a straight line and at a constant velocity.

9. It is the derived quantity that is measured in metres per second and is calculated by dividing displacement by interval of time.

10. It is a quantity, which can be positive or negative, that measures the change in speed over time.

Creating the finest fragrances

On a daily basis we indulge in perfumes and colognes, with an endless array of commercial brands available. But do we truly understand the process behind crafting these captivating scents?

With roots tracing back to ancient times, it was the Arabs who refined the art of perfume-making by introducing the distillation process. Building upon this tradition, alchemists continued to innovate, sourcing new ingredients and essences from both plants and animals in nature.

While the modern perfume industry predominantly relies on synthetic derivatives due to their costeffectiveness, natural essences still hold sway in the realm of high-end fragrances. The extraction of these natural aromas involves various techniques. Distillation, for instance, is a common method where the aromatic components of a plant are steeped in water for hours before being distilled in a still. The resulting steam carries the essences, which are then easily separated upon condensation.

In cases where heating would compromise the aromatic integrity, alternative methods are employed. One such approach involves direct squeezing of the plant material, followed by decanting and filtering the juice to isolate the essence. This technique is particularly suitable for delicate aromas found in citrus fruits, which could be lost under the high temperatures required for distillation.

For particularly delicate raw materials, a direct extraction method is used. This entails immersing the aromatic source in solvents such as alcohol, which extract the essence. The essence is subsequently separated through solvent evaporation.

Regardless of the extraction method, crafting a perfume is as much an art as it is a science. It requires a delicate balance of blending aromas to create a composition that appeals to the olfactory senses of millions.

Think about it

The perfume industry, especially luxury fragrances, is of great economic importance. Perfumes made with natural essences are considered high-end products and are protected by patents.

According to the text, when did perfume making start?

How is perfume making related to chemistry, as outlined in the text? Is making a successful perfume straightforward? Explain your answer.

Discuss your conclusions

What are your thoughts on the cosmetics industry in general? Do you find it beneficial? Share your views.