y r t s mi
Che
3
o hav o vw
Sample chapter
1.1 Introduction to chemistry 1.2 Properties of substances
1.3 Pure substances and mixtures 1.4 Types of mixtures
1
Chemistry and substances
Exploring
Chemistry is a new subject this year. Chemistry is a natural science, along with physics and biology. Chemistry is the most modern of these three sciences. For centuries physicists have been studying stars and planets with telescopes, and biologists have used microscopes to study microorganisms and cells.
Chemistry is about substances. Everything around you consists of substances: air, water, food and textiles. Substances such as copper, diamond and alcohol have been known for a long time. But why is copper flexible, diamond extremely hard and alcohol flammable? You will understand these characteristics when you learn about the extremely small particles which make up these substances. These particles cannot be seen with an ordinary microscope. It is quite hard to imagine something that you cannot see. Chemists began to understand the properties of substances just 150 years ago. Hopefully you will too, with the aid of this book!
I
What do you already know about substances?
Twelve substances are described below. Match the appropriate substance to each description.
1. In chemistry this substance is often given by the formula H2O. 2. This substance is present in the atmosphere and protects us from UV radiation from the sun. 3. You put very little of this substance in your tea because it is 200 times sweeter than sugar. 4. This heavy substance is found in house roofs, for example. 5. All our inherited characteristics are contained in this substance. 6. It may sound strange, but your stomach contains this aggressive substance. 7. This substance is essential for combustion. 8. This substance is commonly known as table salt. 9. This substance is often used in thermometers. 10. This substance is the extinguishing agent in certain fire extinguishers. 11. This substance is used in airships and children’s balloons. 12. Oxygen binds to this substance in the blood.
Ch1
Chemistry and substances
A Alcohol B Aspartame C DNA D Helium E Haemoglobin F Carbon dioxide G Lead H Sodium chloride I Ozone J Water K Hydrochloric acid L Oxygen
6
7
Discovering
Chemistry: a new subject It’s always fun to study a new subject! With a new subject such as German or biology you usually know what the subject is about before your first lesson. With chemistry it is harder to imagine what you will be studying. However, chemistry is nearer by than you may think. Everyday processes such as the combustion of natural gas, blood clotting, rust forming on your bicycle and the effect of medicines are chemical phenomena. Chemistry may make you think of spectacular experiments. Such experiments will enable you to put on a good show at open days, for example.
Activity 1 Surprising chemical experiments A Fresh orange juice (demonstration)
Fresh orange juice is obtained from oranges, of course. Wouldn’t it be easier if it could be made from water?
B The magic glove
Do you need to blow up some balloons for a party? Disposable hospital gloves are just like balloons, but they are much easier to inflate!
C Super-shampoo
Would a self-foaming shampoo be useful?
D Intelligent fruit drink syrup
Do you fancy strawberry or would you rather have lemon? You just have to tell this fruit syrup before you pour it out!
E Powerful breath!
FIG 1.1
You will carry out the following experiments in groups of two or three students, apart from experiment A. Your teacher will assign the experiments to the groups and give further instructions. Do a trial run of the experiment, then use your imagination and present the experiment to the class as a type of magic trick. However, chemistry has nothing to do with magic, which will become increasingly clear as you study this book! Do Activity 1.
F Stain removal salt
A huge stain on your new white trousers? No problem for a chemist!
G Miracle foam
Can you create foam without using a single drop of water?
H Swamp light
How can you put a burning candle at the bottom of a glass of water?
I
The burning bank note
Can you set fire to a bank note without damaging it? A pointless question, perhaps... or is it?!
Your teacher will give you instructions for each experiment. Your teacher will discuss the information on safety on page 11 before you start.
You breathe in and out hundreds of times a day. But did you know that your exhaled breath is rather special?
J The magic finger
Push peppercorns away without touching them. The power of thought, or just some hidden chemistry?
K Lovebite
8
Imitation of a lovebite, without lips...
1.1
Introduction to chemistry
Understanding
What is chemistry about?
You may have already done some chemistry as part of general science lessons in year 2. You will often carry out experiments in chemistry lessons. This is also the case with physics and biology. These three subjects are called natural sciences. In biology you learn about living things and in physics you study phenomena such as light, forces and electricity. In chemistry you learn about substances and chemical reactions (often just called reactions) between substances.
Substances
You can see substances everywhere around you. You can almost certainly see objects made from steel, wood and plastic somewhere. A car, your food, your clothes, and your own body are made of substances. Gases such as oxygen and helium are also substances, even though you cannot see or hold them. There are millions of substances in the natural world. Some of these natural materials are almost ready to use, for example cotton for making clothes and wood for doors. In addition humans have made other materials such as artificial fertiliser, nylon and the sweetener that is used in diet fizzy drinks. Chemists continue to develop new substances in the laboratory, for example better fuels and medicines.
FIG 1.2 Does chemistry look like this?
Have you ever seen a performance by a magician? Impossible things seem to happen. A piece of paper catches fire spontaneously or a solid piece of metal becomes soft and bends. Objects seem to disappear. A white cloth suddenly turns into a live dove. The magician has practiced for years to make you look in the wrong direction and hence draw the wrong conclusions. A chemistry experiment may sometimes seem like a magic trick, but in chemistry lessons you will be told what to observe and be given an explanation of what happens. This book will help you to start to understand chemistry.
Key terms
Chemistry, natural sciences, substance, chemical reaction, research question, work plan, observation, conclusion, report, safety.
Ch1
Chemistry and substances
FIG 1.3 Medicines are also substances.
Reactions
When substances react together new substances are formed. Take the combustion of petrol in the engine of a moped as an example. The petrol reacts with oxygen from the air and other substances are formed. These other substances make up the exhaust gases. Chemical reactions also take place in your own body. Consider the digestion of food, your hair growing and getting a tan at the beach. Characteristic of all reactions is that substances are used up and other substances are formed.
9
Understanding
When water freezes ice is formed. Ice is water in the solid phase. It appears that the water has gone. However ice and water are not different substances: when you melt ice you get water. In other words a change of phase is not a reaction. The same is true when sugar dissolves. When you dissolve sugar in a cup of tea, it appears that the sugar has disappeared. When you drink the tea you can still taste the sugar, so the substance has not disappeared: dissolving a substance is therefore not a reaction.
A scientific investigation begins with a research question. This could be, for example, does vitamin C aid recovery from flu? You then write down a work plan including the materials required and how the experiment will be carried out. For example, one group of people get a daily pill with vitamin C and a control group get a pill without vitamin C.
FIG 1.5 “Does vitamin C aid recovery from flu?” is a research question.
You then carry out your observations. Observation involves your senses. In this case you want to determine if someone has flu. Does the patient cough frequently? Does he have a blocked nose or a sore throat? Sometimes you use a measuring instrument for your observations, for example a thermometer to determine if someone has a fever.
FIG 1.4 Melting ice is not a reaction.
Chemistry, physics and biology are natural sciences. Chemistry is about substances and their reactions. In a reaction substances are converted into other substances. A change of phase is not a reaction.
Scientific research Activity 2, page 13. Many discoveries and inventions are the result of scientific research, for example computers and satellites, as well as vaccines and medicines for all sorts of illnesses. Research is mostly done in universities, hospitals and industrial laboratories.
10
You then draw a conclusion from these observations by thinking about your results. The conclusion answers the research question. In this case scientific research has shown that it doesn’t matter if you take vitamin C when you have flu. The difference between observation and conclusion is also clearly demonstrated by the following example. A police officer sees a suspect’s car in a car park. The car engine is still hot. These are two observations. From this the policeman deduces that the car has been parked for just a short time, and the suspect is probably nearby. These are two conclusions. Sometimes you will write up your experiment in a report. See Appendix 1: The report on page 192.
1.1
Introduction to chemistry
Scientific research starts with a research question. Then you carry out experiments following a work plan. You make observations using your senses or measuring instruments. Finally you think about your results and draw a conclusion that answers the research question.
Safety in the laboratory Activity 3, page 13. During experiments you often use a burner and glasswork and work with dangerous substances. Safety is therefore a top priority! Work calmly and follow the safety rules carefully. The most important rules are: • Check the location of the shower, fire blanket and other safety measures. • Wear a laboratory coat and safety glasses. • Tie up long hair when working with the burner.
Understanding
Alchemists The search for a substance that would turn lead into gold occupied early experimenters for centuries. This substance would also cure all ills, and perhaps even make people immortal. This mysterious substance was known as the Philosopher’s stone. The experimenters, called alchemists, thought that they could make this Philosopher’s stone if they found the right ingredients and secret experiments. Most experimental alchemy in this part of Europe took place in the middle Ages; in other regions it occurred much earlier. We now know that such a substance does not exist. The alchemists’ search was not in vain, however; they developed techniques such as distillation (section 4.3) and made new substances such as gunpowder. As chemical knowledge expanded the philosophy of the alchemists slowly but surely disappeared, though many of their discoveries are still valid in modern day chemistry.
Some experiments produce chemical waste. The less waste, the better, therefore small amounts of substances should be used. Some substances can be washed down the sink, such as salt and alcohol. Other substances such as heavy metals and petrol must be collected for disposal. See Appendix 2: Doing experiments on pages 192/193.
FIG 1.7 Alchemists still sometimes turn up in computer games.
FIG 1.6 Carrying out experiments safely.
Ch1
Chemistry and substances
11
Understanding
Questions: Understanding 1
Chemistry is everywhere. a Name three substances which are used in a chip shop (snack bar). b Give an example of a chemical reaction in the kitchen.
7 Four statements about cola are given below. Explain if
each statement is an observation or a conclusion. a Cola is a dark brown liquid containing small gas bubbles. b Cola is bad for your teeth. c Cola tastes sweet. d One glass of cola contains the same amount of sugar as ten sugar lumps.
2 During a chemical reaction substances are transformed into different substances. a Which substances are changed into different substances when rust forms on a bicycle? b Which substance is formed on the heating element of a kettle or washing machine?
3 Which of the following cases involves a chemical
reaction? Explain your answer. Melting candle wax. Burning candle wax. Fermentation of grape juice. Breaking glass.
a b c d
4 New substances are still being developed, for example glue which fills small holes in a bicycle tyre to prevent flat tyres. Think of another substance that you think should be invented.
5 Suppose you are going to investigate whether nylon
clothes are dangerous when working with the burner. a Write a work plan for this research. b Write down a possible observation. c Which conclusion can you draw from this observation?
6 During a scientific investigation into the effect of vitamin C on health half of the test subjects are given a pill containing vitamin C. The other test subjects are given a pill without vitamin C. This type of pill is called a placebo. The test subjects don’t know if they have received vitamin C or not. The doctors performing the research also don’t know who was given vitamin C and who was not. This type of research is called a doubleblind trial. a Why are half of the patients given a placebo? b Why are the doctors not told who has received vitamin C and who has not? c Explain the term double-blind trial.
12
FIG 1.8
8 Tap water contains dissolved substances such as calcium which can affect your experiments. For this reason you don’t generally use tap water in laboratory experiments. Instead you use tap water from which the dissolved salts have been removed. You suspect that someone in the class has accidentally filled the pure water siphon bottle with tap water. You can’t see the difference, so you want to determine if the siphon bottle contains pure water or tap water using an experiment. When doing chemical experiments you are not permitted to taste anything. a Why is it not permissible to taste anything in chemistry? b Write a work plan for this experiment. c Give two possible dangers with this experiment. d Give a possible observation and the appropriate conclusion with this experiment.
9 a Give four safety rules regarding practical work in the laboratory.
b Draw a sketch of the laboratory and on it show the location of safety features with which you can limit the effects of an accident.
10 Read the paragraph about alchemists on page 11 and
answer the following questions. a Which reaction did alchemists want to carry out? b Give two similarities between alchemy and chemistry. c Give one significant difference between alchemy and chemistry.
1.1
Introduction to chemistry
Experimenting
Activity 2 Mysterious currants
What to do
You can do surprising experiments with substances and materials from the kitchen.
• Add a small amount of tap water to the currants and let them soak. • Put a large spoonful of soda into the large glass beaker. Fill the beaker half-full with water and stir until the soda has dissolved. • Add vinegar until the beaker is almost full. Then quickly add the currants to the beaker.
You will need • • • • •
five currants in a small glass beaker 100 mL glass beaker spatula or spoon soda vinegar
Questions a Write down five observations accurately. b Give an explanation for each observation (conclusion).
Activity 3 Using the burner You will learn to work safely with the burner in this Activity. Also see Appendix 2: Doing experiments on pages 192/193.
You will need • rack with test tubes • burner • siphon bottle with water • wooden test tube peg • a concentrated solution of copper chloride + sodium chloride (blue) • tripod gauze
What to do • Take the burner apart. Investigate how the gas and air flow through the burner. • Put the burner back together again, close the gas inlet and rotate the air inlet upwards. • Attach the tube to the gas tap. Open the gas supply on your bench. • Light the burner: hold a flame by the chimney of the burner and then slowly open the gas inlet valve. Note down the colour of the flame. • Open the gas inlet until the flame is about 10 cm high. • Fill a test tube a quarter full with water. Attach the wooden peg to the top of the test tube. • Holding the test tube by the peg, place the test tube in the flame at an angle and gently move the test tube to and fro. Do not hold the peg in the flame and do not aim the test tube towards yourself or others. What do you see?
Ch1
Chemistry and substances
a Give two reasons why this flame is not used for heating. • • • •
Fill a clean test tube a quarter full with the blue solution. Turn the air inlet downwards until the colour of the flame has just vanished. This flame is suitable for heating small amounts of liquid. Heat the blue solution until something occurs. Do not allow the liquid to boil. Put the test tube aside when it has cooled and turn the air inlet up again.
Environment: Your teacher will tell you how to dispose of the remains of the blue solution.
b Why is it necessary to open the air inlet after each experiment? • •
•
c
Turn the air inlet most of the way down. What does the flame look like now? Using the peg hold the gauze vertically on the burner chimney until the gauze starts to glow. Look carefully to see where the gauze is glowing. Carefully put the gauze aside (caution: hot!) and turn the air inlet up again. Close the gas tap and the gas adjustment on the burner. Explain where the hottest place in the flame is.
13
Discovering Fake cocaine
Do Activity 4.
Investigators have recently tracked down a criminal gang dealing cocaine. An undercover police officer is given the task of delivering several kilos of fake cocaine to the gang. When the criminals take the delivery, police officers will move in to arrest them. The investigators need to have a substance which appears very similar to cocaine.
Main question
End result Write a report of about 150 words advising the police investigators which of the six substances is most suitable for use as fake cocaine. The minimum requirement for your report is that you explain why you have chosen this substance.
Find the answer You are going to compare the substance properties of six substances with those of cocaine. Substance
Colour
Cocaine Chalk Baking powder Flour Glucose Camphor Table salt
white
FIG 1.9
14
Do Activity 5. 2 Fill in the last three columns of the table.
Which substance is sufficiently similar to cocaine that it can be used as fake cocaine?
TABLE 1.1
1 a Copy Table 1.1 and write your observations from Activity 4 in the first three columns. b Explain if this information enables you to decide which substance is most suitable for use as fake cocaine.
Phase (at 25 째C) solid
Smell
In water
In hydrochloric acid
Flammable
none dissolves dissolves
yes
1.2
Properties of substances
Discovering
Activity 4 What can you observe about the substances?
What to do
You will investigate what you can observe about several substances.
• Look at the colour and the phase of all of the substances. • Carefully smell each substance.
You will need • • • • • •
chalk baking powder flour glucose camphor table salt
Activity 5 Further research You will investigate three other substance properties: does the substance dissolve in water, does the substance react with hydrochloric acid and is the substance flammable.
You will need • • • • • • • •
test tube rack with test tubes siphon bottle with water the same six substances used in Activity 4 spatula burner test tube peg six test tube bungs hydrochloric acid
What to do • • • • • • • •
Take six test tubes and using the spatula place a small amount of one of the six substances in each. Add about 6 cm of water to each test tube and seal with a bung. Shake the test tubes. Note down whether or not the substance dissolves. Clean the test tubes. Again put a small spatula of one of the six substances in each test tube. Add about 3 cm of hydrochloric acid. Seal the test tubes and note down your observations. Light the burner. Hold the spatula with the clamp. Take a small amount of each of the substances in turn on the spatula and hold in a colourless flame. Note down if the substance is flammable.
Ch1
Chemistry and substances
FIG 1.10
15
Understanding
You are going on holiday by plane. Your baggage is checked at security. Your bag contains a tub of pills; they are hay fever pills, but the security officer doesn’t believe you. He thinks that you are trying to smuggle ecstasy pills. A pill is removed for testing, and it soon turns out that everything is fine and you are still in time to catch your flight. Clearly the officer can’t tell from the outside if the pill contains ecstasy, so they do a test. How can substances be identified?
FIG 1.12 Colour is a very obvious substance property.
Substances can be identified by their substance properties. Examples of substance properties are colour, odour, flavour, solubility and flammability. FIG 1.11 Baggage scan at the airport
Melting point, boiling point and density Key terms
Solubility, flammability, substance property, melting point, boiling point, density, reactant, reaction product, molecule, van der Waals’ force.
Substance properties Activity 6, page 22. One difference between salt and pepper is immediately obvious: salt is white and pepper is coloured. The colour is not the only difference. If you put both substances in water the salt dissolves while the pepper remains floating on the surface of the water. In other words, their solubility in water differs. Salt and sugar are not so easy to tell apart. They are both white substances which dissolve easily. You would certainly notice the difference if you put salt in your tea or sugar on your boiled egg. Another difference between salt and sugar is their flammability. Sugar burns but salt does not. A third example is water and alcohol. Both are colourless liquids, but smelling them is sufficient to tell them apart, because alcohol has a characteristic smell and water has no smell. The above properties can therefore be used to identify substances, hence they are called substance properties.
16
The difference between water and sugar can be seen immediately: water is liquid and sugar is solid at room temperature (25 °C). In this case the phase of the substance at room temperature is sufficient to identify these substances. The phase of a substance depends on the temperature. Water is solid below 0 °C and becomes liquid at 0 °C, which is the melting point of water. Water becomes a gas at 100 °C and this is the boiling point of water. Alcohol has a melting point of -114 °C and a boiling point of 78 °C. The melting point and boiling point are characteristic for a particular substance. These substance properties are more suitable for identifying substances than their phases. A piece of iron could be small and light, but it could also be large and heavy. The volume and the mass of an object therefore tell you nothing about the substance from which that object is made, as these are not substance properties. The mass divided by the volume is called the density. The most commonly used units are g (gram) for mass and cm3 (cubic centimetre) for volume. This gives the g/cm3 (grams per cubic centimetre) as the unit of density. The density of iron is 7,8 g/cm3. Iron can be identified by its density. Density is therefore a substance property. Melting point, boiling point and density are substance properties.
1.2
Properties of substances
Identifying reactions
When grape juice is allowed to ferment it turns into wine. During fermentation glucose (a natural sugar) is converted into alcohol and carbon dioxide (fizzy gas bubbles). You can taste that a reaction has taken place here, because alcohol has a different flavour than glucose. In addition there are small bubbles of gas in the wine: this is carbon dioxide. With fermentation glucose is the reactant. Alcohol and carbon dioxide are the reaction products. There are noticeable differences between the reactant and the reaction products: in this case the flavour and the phase. From this you can deduce that different substances have been formed and therefore a reaction has taken place. A reaction can often be identified by gas formation and changes in colour, odour or solubility. With a reaction you can observe that the properties of the reactants are different to the properties of the reaction products.
Substances and molecules
Understanding
Molecules enable you to explain the following: • Iodine is a solid purple substance at room temperature. Iodine molecules are relatively large and heavy. The molecules are strongly attracted to each other and are close together. This is why a substance in the solid phase has a high density. The attraction between molecules is called the van der Waals’ force. This force means that molecules in the solid phase cannot move from their positions; they can just vibrate a little. The higher the temperature, the greater the vibration. • Bromine is a brown liquid at room temperature. Bromine molecules are slightly smaller and lighter than iodine molecules. They do attract each other, but they are able to move alongside each other. This is why you can pour a liquid such as bromine. • Chlorine is a yellow-green gas at room temperature. Chlorine molecules are smaller and lighter than bromine molecules. The molecules do not attract each other, and move in all directions. There are no van der Waals’ forces in a gas. There is a lot of space between the molecules. The density of gases is therefore very small.
The majority of substances consist of molecules. These are extremely small particles. One sugar lump contains 9 thousand trillion sugar molecules: this is 9 followed by 21 zeros! One sugar molecule is therefore extremely small. Chemists study molecules in order to understand the properties of substances. Take the odour of perfume, for example. When perfume evaporates molecules from the perfume enter your nose. High in your nasal cavity there are nerve cells called receptors (‘receivers’) which detect smell. The receptors detect the perfume molecules. The receptors then send a signal to your brain, and you smell the scent of the perfume. There are millions of different substances and therefore there are also millions of different molecules. Molecules determine the properties of a substance. The substances iodine, bromine and chlorine consist of iodine molecules, bromine molecules and chlorine molecules respectively. These substances are similar in terms of their substance properties. They are all used as disinfectants and react in a similar way. This is because the molecules of these substances have many similarities. The phase of these disinfectants at room temperature does however differ.
Ch1
Chemistry and substances
FIG 1.13 Perfume molecules reach your nose.
Most substances consist of molecules, which are extremely small particles. Molecules determine the properties of substances. The molecules in a solid and in a liquid are held together by van der Waals’ forces. The heavier the molecules are, the stronger the van der Waals’ force between the molecules.
17
Understanding
Figure 1.14 shows a diagram of the molecules of a substance in different phases. Each ball represents one molecule. This is done for simplicity: not all molecules are ball-shaped. They can also be long and thin, for example.
During melting, evaporation and sublimation molecular bonds are broken, which uses energy. During solidification, condensation and deposition bonds are formed, releasing energy.
Ice = molecule
deposition
evaporation
gas sublimation
condensation
solidification
melting
solid
liquid
FIG 1.14 Molecular models of a solid, a liquid and a gas
It’s actually quite amazing that we can skate on lakes and ponds during winter. This is due to the special properties of water. As the temperature falls, all molecules, including water molecules, move more slowly. At the freezing point the attractive force between the molecules is so strong that the water molecules can no longer move alongside each other. Liquid water becomes solid ice. In almost all substances the molecules get closer together during the transition from liquid to solid, so the density increases. This is why solid candle wax is heavier than liquid candle wax and solid iron is heavier than liquid iron. You can also see this with melting deep-frying fat. Water, however, is an exception: during freezing the space between the molecules actually increases. The volume then increases, and the density decreases. Ice is therefore lighter than water. This means that ice does not sink to the bottom of lakes and ponds, but floats at the top. If it is thick enough it will support your weight and even the weight of an ice-yacht.
Phase transitions such as evaporation can be described accurately using molecular models. When a liquid, for example alcohol, is heated, the molecules move increasingly faster. Some molecules move so fast that they escape from the alcohol: the bond between the molecules is broken. This process uses energy. You notice this when you apply perfume or aftershave that contains a large proportion of alcohol, because your skin cools as the alcohol evaporates. The warmth of your skin is used to evaporate the alcohol. At a certain temperature the molecules move so fast that the liquid starts to boil. This happens at 78 °C for alcohol. When alcohol boils, the density becomes approximately 500 times lower. The substance is the same; the molecules are unchanged. When gaseous alcohol is cooled, bonds form again between the alcohol molecules. The alcohol condenses and droplets form. This process releases energy. Similarly molecular bonds are broken or formed during the other phase transitions. Activities 7 and 8, pages 22 and 23.
18
FIG 1.15 Sailing on ice is only possible because ice is lighter than water.
1.2
Properties of substances
Questions: Understanding 11 Substances can be identified by their substance properties. a Give three properties which enable you to identify water. b Give three properties which enable you to identify gold.
Understanding
Fortunately ‘breathable’ fabrics such as Gore-Tex® are available. Jackets, trousers and shoes made of this material allow water vapour through but keep rainwater out. This is due to very small holes in the fabric. a Show how water vapour is able to travel through this fabric to the outside, using a drawing of a model. b Why is it not possible for raindrops to get inside? c If you are extremely active you will still get wet in breathable clothing. Give an explanation for this.
12 Aluminium is widely used in the construction of aeroplanes. Name two properties of aluminium that make this substance suitable for this application.
13 Three reactions are given below. For each give two
substance properties which differ between the reactant and the reaction product. a A nail rusting. b Frying an egg. c Milk turning sour.
14 The following table gives the melting point and boiling point of a number of substances. Determine the phase at room temperature (25 °C) for each substance. Substance Acetone Aluminium Ammonia Acetic acid
Melting point - 95 °C 660 °C - 78 °C 17 °C
Boiling point 56 °C 2519 °C -33 °C 118 °C
TABLE 1.2
15 A solid, gold-coloured ornament has a mass of 65 g and
a volume of 5,0 cm3. The density of gold is 19,3 g/cm3. Find out if this object could be made of pure gold.
16 Read the paragraph about ice on the previous page
again and answer the following questions. a Why can water pipes burst during a cold winter? b Explain in which way the freezing of water is an exception compared to the solidification of other substances. Include a drawing of a model of water and ice in your answer.
FIG 1.16 Breathable clothing for outdoor sports
18 If you want to make your own candles you first have to heat up solid candle wax. The candle wax melts after a time, but you have to keep heating it before it melts. a Which force holds the molecules in candle wax together? b What happens to the molecules when you heat solid candle wax?
19 Carbon dioxide is used as a fire extinguishing agent.
17 When you do outdoor activities there is always a chance that it will rain and you get wet. It is therefore a good idea to wear waterproof clothing. If you wear an ordinary rain jacket you will still get damp from your own sweat.
Ch1
Chemistry and substances
In a fire extinguisher carbon dioxide is converted into a liquid under high pressure. When the pressure is released the carbon dioxide boils and the temperature falls significantly. Using the van der Waals’ force, explain why the temperature falls when carbon dioxide starts boiling.
19
Knowing more
Solubility
Suppose that you add sugar lumps to a glass of water. The first sugar lump dissolves easily, and so do the next few. The solution obtained is still unsaturated. If you keep adding sugar lumps, at a certain point sugar will remain undissolved at the bottom of the glass. Even if you stir the water for a long time no more sugar will dissolve. The solution is then saturated.
solubilityd (g/L)
The maximum number of grams of a substance that can be dissolved in one litre of water is called the solubility in water. The solubility of sugar in water at room temperature is approximately 2 kilograms per litre. This solubility is a substance property. The solubility depends upon the type of substance which is being dissolved, and thus the type of molecules. Substances such as marble and petrol are very poorly soluble in water, so their solubility is almost 0 grams per litre.
The solubility of a particular substance depends upon the temperature. For example, you can dissolve more sugar in hot water than you can in cold water. This is true of almost all solid substances. With gases the opposite is true: at higher temperature the solubility of gases decreases. This is why the fizz is soon lost in a glass of warm cola. This is also true of other gases. Rivers and lakes are depleted of oxygen in a hot summer, which can cause fish to die. The solubility of a substance in water is the maximum number of grams of that substance which dissolve in one litre of water. The solution is then saturated. The solubility in water is a substance property that depends only upon the temperature.
Example calculation
5000
Suppose you try to dissolve 400 g sugar in 150 mL water at 40 °C. Using figure 1.17 calculate how many grams of sugar remain at the bottom of the glass. Hint: first calculate how many grams can be dissolved in 150 mL water.
4000 3000
2000
Solution: from the graph read off the solubility of sugar in water at 40 °C: 2400 g/L. 1 L = 1000 mL
1000
0
5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100
: 1000
× 150
o
temperature ( C) FIG 1.17 The solubility of sugar in water at various temperatures
The solubility is not dependent upon how fine a substance is: finely ground sugar and granulated sugar contain the same molecules and therefore have the same solubility. Finely ground sugar will certainly dissolve faster. Stirring and shaking also make a substance dissolve faster, but the amount that can be dissolved does not change. Activity 9, page 23.
20
sugar water
2400 g 1000 mL
2,4 g 1 mL : 1000
? 150 mL × 150
? = 2,4 g × 150 = 360 g Amount of sugar that dissolves in 150 mL water at 40 °C is 360 g. Therefore 400 g − 360 g = 40 g sugar remains at the bottom of the glass.
1.2
Properties of substances
Questions: Knowing more
Knowing more
24 In the Netherlands salt is obtained from below ground by dissolving it in water. The salty water (brine) is then pumped up. Describe how you could use an experiment to determine if the brine is a saturated or unsaturated salt solution.
20 Hot water is used to dissolve the sugar from sugar beet in a sugar factory. 750 kg of sugar is dissolved in 250 L water at 90 °C. Then the solution is cooled, whereby crystals of sugar are formed. a Think of two reasons why hot water is used. b Show using a calculation and figure 1.17 that this solution is unsaturated at 90 °C. c Determine the temperature at which sugar crystals start to form.
21 Salmiak is a flavouring used in liquorice and other
25 A hand warmer is a small packet containing a liquid which turns solid and releases heat when you bend a small metal disc in the packet. This occurs because crystals form in the solution. A particular hand warmer contains 25 g sodium acetate and 25 mL water. Table 1.3 gives the solubility of sodium acetate at various temperatures.
sweets. The solubility of salmiak in water at room temperature is 393 g/L. To investigate if an unknown substance is salmiak you determine the solubility of that substance at room temperature. The maximum amount of this substance that dissolves in 20 mL water is 6.3 g. Explain if the unknown substance could be salmiak.
Temperature in °C 0 20 40 60 80 100
22 The solubility of table salt in water at room temperature
is 360 g/L. You try to dissolve 25 g table salt in 50 mL water. a Show using a calculation that the solution obtained is saturated. b Calculate how many grams of table salt remain at the bottom.
FIG 1.18 Salting icy roads is effective because salt dissolves easily.
23 When you bring tap water to the boil you see small bubbles form before the boiling point has been reached. These bubbles are not water vapour and no reaction is taking place. Give an explanation for the appearance of these gas bubbles.
Ch1
Chemistry and substances
Solubility in g/L 362 464 656 1390 1530 1700
TABLE 1.3
a Plot the data in Table 1.3 in a graph. Put the
temperature on the x-axis and the solubility on the y-axis. b Show with a calculation that the solution in the hand warmer is saturated at room temperature (25 °C). A hand warmer is ‘charged’ by heating it in a pan of hot water until the sodium acetate is completely dissolved. When the hand warmer then cools to room temperature no solid sodium acetate forms, but a so-called supersaturated solution is produced. Bending a metal disc in the hand warmer causes the solution to start to crystallise. This releases enough heat to raise the temperature of the hand warmer by about 20 °C, which is pleasantly warm when you have cold hands. c What is the minimum temperature the hand warmer must be heated to so that all the sodium acetate dissolves? Use your graph. d Why does the temperature of the hand warmer rise when the sodium acetate crystallises? e Calculate how many grams of solid sodium acetate form in the hand warmer at 40 °C.
21
Experimenting
Activity 6 Forensics lab Watch the video clip about the Forensics lab on www.impact-online.nl and answer the following questions. • Which substances are the Forensics team interested in when investigating a crime? • How can the Forensics experts find ‘invisible traces’? • Various training courses such as the HBO in Forensic Research require you to have studied chemistry. Think of two reasons why this is necessary.
FIG 1.19 Forensic research
Activity 7 Water in a can (demonstration)
What to do •
You will need • • • • •
empty fizzy drink can crucible tongs tripod with gauze burner container with water
•
Put a small amount of water in the can and heat the can until the water boils. Hold the can with the tongs and quickly turn it upside down in the container of water. What happens?
Questions a What happens to the water molecules during heating? Use two drawings to explain your answer.
b Give an explanation for your observations as the water cools.
22
1.2
Properties of substances
Experimenting
Activity 8 Making salty liquorice (demonstration)
You will need
You might think that you have to bring two substances in close contact with each other in order that they react. But is this always true?
• • • •
concentrated hydrochloric acid concentrated ammonia two watch glasses dark coloured paper
What to do • •
Inside the fume cupboard place a few drops of hydrochloric acid on one watch glass and a few drops of ammonia on the other watch glass. Place the watch glasses next to each other in front of a dark background. What do you observe?
Questions a How can you see that a reaction has taken place?
FIG 1.20 Salmiak balls
b
The substance formed is salmiak, familiar from salty liquorice sweets. Explain using molecules how a reaction has taken place here without both liquids being mixed together.
Activity 9 Solubility and temperature
•
You will need • • • • •
test tube rack with test tubes siphon bottle with water wooden test tube holder burner oxalic acid
What to do •
Put a large spatula of oxalic acid into a test tube. Add several millilitres of water and shake the test tube well. What happens?
Ch1
Chemistry and substances
•
Clamp the test tube in a wooden test tube holder. Heat the test tube carefully using a colourless flame and moving the test tube continually, until all the oxalic acid has dissolved. Caution: do not allow the liquid to boil. Cool the test tube under a cold tap or in iced water. What happens?
Questions a How does the solubility of oxalic acid differ in cold water compared to hot water?
b Give an explanation for the observations during cooling.
23
Discovering
Healthy choices If you go on holiday without your parents you will probably do your own shopping. There is plenty of choice: you can buy thousands of items in the supermarket. You can choose expensive top brands or cheap home brands, fresh produce or ready-made meals. Some products have a ‘healthy choice’ symbol. Low-fat margarine has this symbol, but butter doesn’t. You can use either to spread on your bread. What’s the difference?
2 a Estimate the percentage of fat in butter. b Do the same for the percentage of fat in low-fat margarine. Most food packaging has a nutrition information label. This includes a table of nutritional values.
Look at Source 2. The nutritional value is the energy provided by 100 g of a product. Butter and low-fat margarine have very different nutritional values. 3 Explain the main reason for this large difference.
Look at Source 3. 4 Which of the ten tips are relevant for butter and low-fat margarine?
End result •
FIG 1.21
Main question Why does low-fat margarine have a ‘healthy choice’ symbol and butter does not?
Find the answer Look at Source 1. 1 Explain in one sentence which products are given this symbol. Butter and low-fat margarine are both mixtures of fat, water and a number of other substances to aid blending.
Do Activity 10. Using the results of Activity 10 you can estimate what percentage of the volume of each type of spread is fat.
24
•
Give three reasons why low-fat margarine is a healthy choice and butter is not. Explain if you can eat as much as you want of ‘healthy choice’ products.
Source 1
‘Healthy choice’ advert
Watch the advert ‘Ik kies bewust’ on www.impact-online.nl The script of the advert is given below. To eat more healthily you don’t have to change your daily eating habits drastically. Start by changing to similar products that have the healthy choice symbol. You eat and drink the same as before, but a little bit healthier. I make a healthy choice. It’s easy to choose for better health.
1.3
Pure substances and mixtures
Activity 10
Source 2
Heating butter and low-fat margarine You will need • • • •
test tube rack with test tubes • 250 mL glass beaker • tap water burner •
spatula low-fat margarine and butter tripod with gauze
What to do • •
•
•
•
Place the glass beaker half full with tap water on the tripod with gauze. Light the burner, open the air inlet until you get a colourless or light blue flame and place the burner under the beaker. When the water is boiling adjust the flame so that the water boils gently. Using the spatula half fill one test tube with butter and half fill another test tube with low-fat margarine. Place both test tubes in the boiling water for a time. Turn the burner off when the contents of both test tubes have melted. Remove the test tubes from the water (caution, hot!). Make a scale drawing of the contents of both test tubes.
Source 3 1. 2.
3. 4. 5.
6. 7. 8. 9. 10.
Table of nutritional values
Nutritional value per 100 g
Butter
Energy Protein Carbohydrate of which sugars Fat of which saturates trans mono-unsaturates
3076 0,7 0,7 0,7 82,5 54 1 23,5
kJ g g g g g g g
polyunsaturates Fibre Salt Vitamin A Vitamin D Vitamin E
3,5 g 0 g 1,90 g 1000 µg 1,2 µg 0 g
Low-fat margarine 1530 kJ 0,1 g 4,9 g 0,1 g 39 g 11,5 g 1 g 14,5 g 12 g 0 g 0,30 g 1000 µg 7,5 µg 18 µg
TABLE 1.4
Ten healthy eating tips Eat a varied diet By eating a varied diet you get all the essential nutrition you need. Limit your fat intake Limit your intake of saturated fat. This does not mean that you can’t eat any fat at all. Fatty foods are also a source of unsaturated fatty acids and vitamins A, D and E. So choose products with less saturated fat and more (good) unsaturated fats. Eat plenty of bread and potatoes Eat generous portions. Together with rice, pasta and pulses and lentils these are a good basis for a healthier diet. Eat plenty of fruit and vegetables Try to eat at least two servings of fruit and 200 g vegetables every day. Get enough exercise Having a healthy weight means that you will live healthier for longer. Make sure you get enough exercise and eat a varied and balanced diet. Use salt sparingly Our body needs salt, but just a small amount is sufficient. You can use herbs and spices for extra flavour instead. Drink plenty of liquid, but not too much alcohol Drink at least one and a half litres of liquid per day, but no more than two to three glasses of alcohol. Don’t eat all day long Three main meals a day are the basis of a healthy diet. Don’t eat snacks between meals where possible. Handle food safely and hygienically Be careful when reheating leftovers, wash your hands frequently and avoid contact between raw and cooked food. Read the packaging The packaging is labelled with information such as the use-by date, ingredients and the nutritional value of the product.
FIG 1.22
Ch1
Discovering
Chemistry and substances
Source: Translated from ‘Ik kies bewust’ pamphlet.
25
Understanding
Margarine contains water, oil and vitamins. Toothpaste contains more than ten different substances, and expensive perfumes can have more than one hundred ingredients. Almost all substances found in nature as well as at home are mixtures. Familiar examples of pure substances are diamond and gold. Sugar is also a pure substance. Sugar is obtained by extracting it from sugar beet. Therefore pure substances can be obtained by extracting them from suitable mixtures. How do you know if a particular substance is a pure substance or a mixture?
Key terms
Mixture, pure substance, melting range, boiling range, concentration (= content), per cent mass, per cent volume.
Identifying mixtures
Mineral water is often labelled ‘pure mineral water’ and fruit juice is often labelled ‘100% pure fruit juice’. It is often said that forest air is ‘pure air’. Are mineral water, fruit juice and forest air really pure? Do they therefore consist of just one substance? The term ‘pure mineral water’ suggests that it contains minerals and water. From a chemical point of view it is therefore not a pure substance, but a mixture. Fruit juice contains mostly water with glucose, and air is mainly nitrogen and oxygen. In everyday life the word ‘pure’ therefore almost always means ‘healthy’ and not ‘chemically pure’.
Melting point and melting range Activity 11, page 32. To find out if candle wax is a pure substance or a mixture you can look at the temperature during the solidification of melted candle wax. If this temperature stays the same during solidification then the candle wax is pure. If the temperature changes during solidification then it is a mixture. This is also true for melting: a solid pure substance has a melting point, whereas a mixture has a melting range. With a melting range the substance begins to melt at a certain temperature and the substance melts entirely at a higher temperature. When performing this test the candle wax is melted first because the temperature measurement during solidification is more reliable than during melting. Something similar is observed when liquids boil. When a pure substance boils the temperature does not change. If you increase the heat of the flame under boiling water the water will boil more energetically (more water vapour bubbles will appear) but the temperature stays the same at 100 °C. When a mixture of water and alcohol boils, mostly alcohol evaporates first. This changes the composition of the mixture, as the remaining mixture contains proportionally more and more water. This means that the temperature during boiling gradually increases. Mixtures therefore do not have a boiling point: they have a boiling range. A boiling range has a start and end temperature. In summary, you can tell pure substances and mixtures apart by measuring the temperature during melting or boiling. If a substance has a melting point and a boiling point then it is a pure substance.
T(oC) FIG 1.23 T he label lists which minerals are dissolved in the mineral water and in what quantities.
Can you see the difference between a mixture and a pure substance? Take cloudy pond water, tap water and pure water, for example. You can see that the pond water is a mixture because there are small solid particles floating in the water. Tap water is clear, but if you evaporate a dish of tap water you are left with a greyish-white layer of calcium. When pure water evaporates nothing at all is left. All cloudy liquids are mixtures. However, as the example of tap water shows, you cannot say that a liquid is pure just because it is clear.
26
gas
T(oC)
gas
liquid+gas
100
liquid+gas
liquid liquid time (min)
time (min)
FIG 1.24 B oiling diagram of water (left) and a mixture of water and alcohol (right)
A pure substance has a melting point and a boiling point. A mixture has a melting range and a boiling range.
1.3
Pure substances and mixtures
Understanding
FIG 1.25 This ice-cream starts melting at below 0 °C.
Ice lollies are a mixture of mostly ice (i.e. water) and sugar. The melting point of pure ice is 0 °C and the melting point of sugar is 170 °C, so you may well think that the melting range of ice lollies must be between 0 and 170 °C. However, ice lollies start to melt at below 0 °C! In other words, the properties of a mixture cannot simply be determined from the properties of the pure substances in that mixture. With ice lollies you are looking at the melting of a mixture of ice and sugar.
Activity 13, page 33. The percentage by mass of a substance in a mixture is calculated using: per cent mass of substance =
mass of substance × 100% mass of mixture
The percentage by volume of a substance in a mixture is calculated using:
Activity 12, page 32. The properties of a mixture cannot always be determined from the properties of the pure substances in that mixture.
Concentration: per cent mass and volume
Two different products may contain the same substances but have a different composition. For example consider ordinary food vinegar and kitchen grade white vinegar for cleaning. Both mixtures contain water and acetic acid, but food vinegar contains about 4 % acetic acid whereas white vinegar contains 8 % acetic acid. Packaging is often labelled with information telling you how much of a given substance is contained in a certain amount of a mixture. A packet of low-fat margarine might be marked ‘contains 40% oil’. This is a per cent mass (short for percentage by mass). 100 g of this margarine therefore contains 40 g oil. Per cent mass is a unit of concentration, or content. For mixture of liquids and mixtures of gases it is more convenient to work with percentage by volume, usually known as per cent volume. Two examples: • 100 mL wine with 12 per cent volume (%vol) alcohol contains 12 mL alcohol. • Air contains 21 per cent volume (%vol) oxygen, so 100 cm3 air contains 21 cm3 oxygen.
Ch1
Chemistry and substances
per cent volume of substance =
volume of substance × 100% volume of mixture
The concentration of a solid substance in a solution is often given using a different unit: grams per litre (g/L). The salt concentration of sea water from the North Sea is given as 34 g/L.
Example calculation The label on a bottle of vodka says 40% vol. The bottle contains 750 mL vodka. How many millilitres of alcohol does a full bottle contain? Solution: 40% alcohol means that 100 mL vodka contains 40 mL alcohol. alcohol vodka
: 100 40 mL 100 mL
0,40 mL 1 mL
: 100
× 750 ? 750 mL × 750
? = 0,40 mL × 750 = 300 mL. The bottle of vodka contains 300 mL alcohol.
27
Understanding
Alcohol and traffic
27 For each of the following mixtures give at least two pure
It is illegal to drive under the influence of alcohol. Even a small amount of alcohol in your blood reduces your concentration and reaction time. Every year about 250 people are killed in traffic accidents in the Netherlands as a result of alcohol consumption. This is why very strict laws are in place and the police carry out regular alcohol checks, in particular in the evenings and during weekends. If you are under 24 and are riding a bicycle, motorised bicycle or moped you can have a maximum of 0,2 per mille of alcohol in your blood. Per mille means per thousand, so this is 0,2 mL alcohol per 1000 mL (1 L) blood. You may reach this after just one glass of beer or wine or one shot of spirits. During a roadside check the police don’t usually determine the alcohol content in the blood. They measure the alcohol content of your breath. The limit for this is 88 μg (micrograms) alcohol per litre of exhaled breath. A microgram is one millionth of a gram. This unit is often called ugl in newspapers, but this is wrong: it should be μg/L.
substances contained in that mixture. a cola b wine c tapwater d air
28 A solid substance is melted and then gently cooled. After a period of time all of the substance has solidified. The temperature is measured every minute during cooling. Table 1.5 gives the temperature with time during solidification. Time (min)
Temperature (ºC)
0 150 1 142 2 136 3 135 4 135 5 134 6 132 7 126 8 120 9 115 10 111 TABLE 1.5
a Plot a graph of these results. Put the time on the x-axis and the temperature on the y-axis. Ask your teacher if you should do this on paper or on the computer. b Explain if the substance is a pure substance or a mixture.
29 The glasses used for different alcoholic drinks are
FIG 1.26 C ould you blow in here, please?
Questions: Understanding 26 The word ‘pure’ has various meanings. a What is meant by the phrase, ‘The water is very pure there’ in day to day terms?
b Explain if this water is also chemically pure.
different sizes. A shot glass is much smaller than a beer glass. But which drink contains the most alcohol per glass? a For each drink in Table 1.6 calculate how many millilitres of alcohol that glass contains. Drink
Percentage of alcohol (%)
Beer 250 5,0 Wine (white) 100 12,0 Dutch gin 35 35,0 Whisky 35 40,0 Shot+mixer 275 5,6 TABLE 1.6
28
Contents of glass (mL)
Amount of alcohol (mL)
1.3
Pure substances and mixtures
The combination of Dutch gin (jenever) and beer is called a ‘head butt’ in the Netherlands: quite an appropriate name! In Belgium the entire shot glass with Dutch gin is put into the beer, and it is called a ‘submarine’. b Calculate how many millilitres of alcohol a ‘submarine’ contains. c Calculate the percentage of alcohol by volume a ‘submarine’ contains. Make sure you use the correct volume for the drink.
Understanding
32 A 25 g bronze medal is made of 88% mass copper and 12% mass tin. Calculate how many of these medals can be made from 3300 g copper (and the appropriate amount of tin).
33 Read the paragraph about alcohol and driving on
keeper gives him a drink containing 50 mL rum and 200 mL cola. The alcohol percentage of this mixture is 8%. a Calculate how many millilitres of alcohol this mixture contains. b Calculate the alcohol percentage of pure rum. c Calculate how much cola you would have to add to 50 mL rum to make a drink which is double the strength, that is, 16% alcohol.
the previous page again and answer the following questions. a One weekend a 20-year-old man drinks two 250 mL bottles of beer with an alcohol content of 4,0%. Calculate how many millilitres of alcohol this young man has consumed. Suppose that 10% of this alcohol enters his bloodstream. The total volume of blood in the body is 4,0 L. b Calculate the amount of alcohol in the man’s blood in per mille. c Can he get on his moped and ride home with this level of alcohol?
31 Gold is a soft metal. In order to prevent gold jewellery
34 The label of a bottle of fruit drink syrup says that the
and coins from bending or wearing quickly it is therefore mixed with other metals. This makes it much harder. The gold content is given in carats. One carat is 1/24 part gold by mass. a Calculate how many grams of gold are in a 12 g, 18 carat coin. A wedding ring is made from 3,5 g gold, 2,0 g silver and 0,5 g copper. b Calculate what carat gold this ring is.
nutritional value is 1245 kJ per mL syrup and 445 kJ per 250 mL glass of fruit drink. Use this information to calculate the proportion by volume that the syrup has to be diluted to make a drink.
30 A customer orders a rum and cola at a cafe. The bar-
FIG 1.27 How much alcohol is in each glass?
Ch1
Chemistry and substances
29
Knowing more
MAC value
At a swimming pool you can sometimes smell the typical odour of chlorine, which is a substance that is used as a disinfectant. The concentration of chlorine in the air must not be too high, as too much chlorine is an irritant and is harmful to health. There is a law regarding the maximum amount of a substance which can be present in a certain space. In the Netherlands this is the maximum accepted concentration (MAC value). For harmful substances the MAC value is relatively low, of course, so it is not convenient to give the concentration in grams per litre or as a percentage. The unit milligrams per cubic metre (mg/m3) is usually used. For low concentrations, calculations often use ppm by mass or ppm by volume. The abbreviation ppm means parts per million. If the concentration of chlorine in the air is 5 ppm by volume, there is 5 cm3 chlorine in one million cm3 air. This is equal to 5 cm3 chlorine per cubic metre of air. ppm by mass =
mass of substance Ă— 1 000 000 mass of mixture
ppm by volume =
volume of substance Ă— 1 000 000 volume of mixture
Table 1.7 gives the MAC values for mercury vapour and a number of gases.
ADI value
Example calculation If you clean a toilet bowl using chlorine bleach, chlorine gas may be released. 15 cm3 chlorine gas is released in a toilet of 6 m3. Calculate the concentration of chlorine in ppm by volume and find out if the MAC value is exceeded. Solution: The ppm by volume of chlorine is the number of cm3 chlorine in 1 000 000 cm3 air. 6 m3 is equal to 6 000 000 cm3. chlorine air
:6 15 cm3 6 000 000 cm3
30
:6
MAC value (mg/m3)
The concentration of chlorine is 2,5 ppm by volume. The MAC value of 1 ppm by volume is therefore exceeded.
MAC value in ppm by volume
mercury vapour 0,05 0,006 chlorine 3 1 ammonia 16 23 carbon monoxide 29 25 carbon dioxide 9000 5000 TABLE 1.7
? 1 000 000 cm3
? = 15 cm3 : 6 = 2,5 cm3
Harmful substances can enter the body via food and drink as well as in the air you breathe. These substances could be pesticide residues, veterinary medicines or environmental pollutants. The maximum intake of these substances is given by an ADI value: the acceptable daily intake. It is assumed that you can consume this amount
Substance
of a substance daily without any risk to your health. The ADI value is usually given in milligrams of substance per kilogram of body weight. For a small child the maximum intake is therefore less than that for an adult. Substances with an E number such as colouring agents, flavourings and preservatives also have an ADI value. These substances have been researched thoroughly and can only be used in foodstuffs in a safe concentration.
1.3
Pure substances and mixtures
Questions: Knowing more 35 Ammonia has a strong odour, whereas carbon monoxide
is odourless. a Explain which of these two substances exceeds the MAC value faster (use Table 30). b Explain if your answer to question a must therefore also be the more dangerous substance.
36 To apply a thin layer of gold to a statuette, gold is first mixed with mercury. The gold amalgam obtained is applied to the statuette, and the statuette is then heated in a furnace. The heat evaporates the mercury and the statuette is gold-plated. Is this actually a safe method? a Calculate how many grams of mercury vapour will exceed the MAC value in a room 15 m × 5 m × 3 m. b Think of a safer method which uses the same substances.
Knowing more
38 If you have a swimming pool in the garden algae and bacteria will soon grow in the water in summer. You can buy tubs of chlorine tablets to disinfect the water. For optimal disinfection the minimum concentration of chlorine in the water must be 2 mg/L. To avoid health risks the maximum chlorine concentration is 5 mg/L. One tablet adds 1,5 g chlorine. a Calculate the minimum number of tablets which must be added to a swimming pool containing 4 m3 water. b Calculate the concentration of chlorine in ppm by mass when the maximum concentration is reached. The density of water is 1,0 g/mL.
39 Aspartame (E951) is an artificial sweetener contained in diet fizzy drinks and other foodstuffs. Diet cola contains 200 mg aspartame per litre. The ADI value for aspartame is 40 mg/kg/day. a How many milligrams aspartame can a 55 kg student consume daily without harming his health? A glass contains 250 mL diet cola. b How many glasses of diet cola do you have to drink to consume the number of milligrams of aspartame you calculated in a? c Explain if it is healthy to drink this many glasses of cola.
FIG 1.28 G ilded using gold amalgam?
37 Painters use ammonia to clean grease from surfaces.
FIG 1.29 T he sugar-free version of this drink contains aspartame.
Ammonia is a solution of ammonia gas in water. A painter uses 250 g ammonia with a concentration of 10% mass in a closed shed of 60 m³. Slowly but surely the ammonia gas enters the air. Calculate if the MAC value will be exceeded when all of the ammonia is released into the shed.
Ch1
Chemistry and substances
31
Experimenting
Activity 11 Candle wax: pure or mixture? In this Activity you will measure the temperature of candle wax as it solidifies.
You will need • • • • • •
tripod with gauze test tube a quarter full of candle wax chips 250 mL tall glass beaker thermometer (computer with temperature sensor) stand with clamp burner
What to do • •
Fill the beaker half full with tap water and place it on the gauze on the tripod. Place the thermometer (or sensor) in the candle wax and place the test tube in the beaker. Check that your set-up cannot fall over.
• Heat the beaker using a colourless, non-roaring flame. Stir carefully with the thermometer (sensor). Continue to heat and stir until all the candle wax has melted. • Remove the test tube (it is hot!) from the water and clamp it to the stand. • Let the candle wax cool. Measure the temperature every 30 s during cooling and note this down (with a sensor this is not necessary). Keep stirring with the thermometer (sensor). Note down after how many minutes the candle wax starts to solidify. • Continue until all of the candle wax is solid. • If using a thermometer: - Plot the results in a graph. Put the time on the x-axis and the temperature on the y-axis. - Indicate the melting point or melting range on the graph.
Question Explain if the candle wax is a pure substance or a mixture.
Activity 12 Ice, water and salt Pure water freezes at 0 °C. Table salt has a melting point of 800 °C. In this experiment you will determine the temperature at which a salt solution starts to freeze.
You will need • • • • •
glass beaker two cold table salt solutions (containing 2% table salt and 10% table salt respectively). antifreeze from the freezer three thermometers (sensors) test tube rack with test tubes 0%
2%
10%
What to do • • • •
Take three test tubes. Put equal amounts of the following liquids in the test tubes: cold water, 2% salt solution, 10% salt solution Fill the beaker with antifreeze from the freezer. Place a thermometer (sensor) in each test tube and place the test tubes in the antifreeze (see figure 1.30). Carefully stir with the thermometers (sensors) and read the temperature when the liquid in a test tube starts to freeze.
FIG 1.30
Questions a Explain if the results were as expected. b Explain how this experiment shows why salt is spread onto icy roads in winter.
c Explain how this experiment shows why more salt is needed per application in very cold winters.
32
1.3
Pure substances and mixtures
Experimenting
Activity 13
Hard water
In chalk-rich areas the ground water contains much more calcium. Water with a high calcium content is called hard water. The hardness of water is given in German hardness units (°DH = Duitse hardheid). 1 °DH is equivalent to 7,1 m calcium per litre of water. 0 to 4 4 to 8 8 to 12 12 to 18 18 to 30 >30
°DH very soft water °DH soft water °DH average water °DH moderately hard water °DH hard water °DH very hard water
very soft water soft water average water moderately hard water hard water
The drinking water company removes some of the calcium from hard water before it reaches your tap. Hard water is not harmful to health, but it does lead to scale deposits in the bathroom and on the heating element of the kettle and washing machine. • Look up on Internet what happens when you make tea with hard water. How can this be prevented? • Look up on Internet what happens when you do the washing with very hard water. How can this be prevented? • Look up on Internet how hard the water in your area is at www.impact-online.nl • Calculate how many grams of calcium are dissolved in the bathwater when you fill your bath at home with 150 L tap water.
Ch1
Chemistry and substances
very soft water soft water average water moderately hard water hard water FIG 1.31 Water hardness: regional differences in the Netherlands
33
Discovering
Mayonnaise When you order chips and mayo at a snack bar you get hot chips with mayonnaise. Mayonnaise has been around for some time. It is said that it was first made in 1756 during the siege of the Spanish city of Mahón. It was almost impossible to find food in the city. To make old bread palatable a chef made a sauce with oil and vinegar: mayonnaise. Just mixing oil and vinegar does not make mayonnaise, however!
A The function of the egg yolk. B The purpose of adding oil in drops instead of all at once. C The function of the salt.
4 Compare the different types of mayonnaise that have been made in class and give the effect of the three factors investigated.
End result Write down in no more than 100 words what is involved in making good mayonnaise.
Activity 14 Oil and vinegar You will investigate what happens when you add oil to vinegar.
FIG 1.32
Main question
You will need • • • •
oil vinegar test tube rack with test tubes test tube bung
How can you make your own mayonnaise?
Find the answer Do Activity 14. 1 Why don’t you get a good mixture in Activity 14?
What to do • Put a small amount of oil and a small amount of vinegar in a test tube. • Seal the tube with a bung and shake the test tube vigorously. • Leave the test tube to stand for a while. Observe what happens.
Look at Source 4. 2 Write down three differences between the substances and methods used in Activity 14 and this recipe for mayonnaise. The differences you named in question 2 are also called factors. You cannot yet say what the effect of each factor is. With a good experiment you don’t change all factors at once, but one at a time. This enables you to find out what the effect of that factor is.
3 Working in groups, investigate the function of the various substances and the instructions for making mayonnaise. Divide the tasks between you. Each group gets the ingredients for the recipe and investigates one of the following factors:
34
Source 4
Recipe for mayonnaise
Ingredients • • • •
1 egg 15 mL vinegar 200 mL vegetable oil 2 grams salt, 3 grams sugar and a pinch of pepper
Carefully break the raw egg in half and pour off the egg white, leaving the egg yolk. Place the yolk, vinegar, salt, sugar and pepper in a bowl and stir together well. Add the oil drop by drop while stirring continuously. When half of the oil has been added, the rest can be added in dashes or spoonfuls.
1.4
Types of mixtures
A chef spends a large amount of time making various mixtures: simmering stock for soup, making mayonnaise for chips, kneading dough for bread rolls and whipping cream for desserts. Stock, mayonnaise, dough and cream all look different and have different textures. For example, stock is clear while mayonnaise is cloudy. Bread is crusty and cream is soft. What determines the properties of these mixtures?
Understanding
Methylated spirits is a clear mixture of alcohol, water and a blue colouring. The colouring is added to warn people that meths is toxic. A solution can therefore also be coloured.
Key terms
Solution, suspension, precipitation, filtration, filtrate, residue, emulsion, emulsifier, foam, smoke, aerosol, hydrophilic, hydrophobic.
Solution and suspension
If you put a small amount of sugar in water and shake it well you get a transparent mixture. It appears that the sugar has disappeared. This type of clear liquid mixture is called a solution. Other solid substances which dissolve easily in water are table salt, soda and salmiak. Some liquids and gases also dissolve well in water: beer is mostly water in which the liquid alcohol and the gas carbon dioxide (the ‘fizz’) are dissolved. The cleaning agent ammonia is a solution of ammonia gas in water.
FIG 1.33 All solutions are clear, and they may also be coloured.
If you shake chalk powder with water the chalk spreads throughout the water but does not dissolve. You obtain a non-transparent liquid with small grains floating in the water.
FIG 1.34 Making mixtures in the kitchen.
Ch1
Chemistry and substances
35
Understanding
This type of cloudy mixture of a solid in a liquid is called a suspension. If you leave a suspension to stand for a while the solid substance sinks to the bottom. Organic apple juice is a suspension of particles of apple in apple juice. If a bottle of this juice has been left to stand for a time most of the apple particles will have sunk to the bottom. So shake well before use!
Separating a suspension
Sewage water is also a suspension: all sorts of solid particles float in it. These solid particles are removed at the water treatment plant in a simple way. The sewage water is left to stand in large tanks. The solid particles automatically sink to the floor and are thus separated from the liquid. This method of separation is called sedimentation. Sedimentation can be used to separate a suspension but not a solution. Activity 15, page 42.
FIG 1.35 Shake before use.
A solution is a clear liquid mixture. A solution can be coloured. A suspension is a cloudy mixture of a solid in a liquid.
You can also separate a suspension using a paper filter. The solid substance, for example chalk powder, is left behind on the filter. This is called the residue. The liquid which passes through the filter is called the filtrate. This method of separation is called filtration. Substances which are dissolved in the liquid therefore also pass through the filter. A solution of sugar and water therefore cannot be separated using a filter. A coffee pad is ground coffee packaged between two layers of filter paper. The coffee is brewed by pressing hot water through the pad. The coffee grounds remain trapped in the filter pad while the dissolved colouring and flavouring compounds pass through the filter with the hot water.
Blood and doping Blood is a complex mixture. During a blood test the blood cells are often separated from the fluid (plasma). This can be done using sedimentation, but it takes hours. Sedimentation can be done more quickly using a centrifuge. A test tube of blood is spun at high speed. The relatively heavy blood cells are then ‘thrown’ outwards, similar to the chair of a chair-plane ride at a fun fair. The blood cells settle at the bottom of the test tube, and the blood plasma with dissolved substances is at the top.
The presence of the substance EPO is difficult to prove, but the red blood cell content is easily determined after centrifuging. This red blood cell count is also called the haematocrit value. If the haematocrit value of a cyclist is above 50% the cyclist is not allowed to participate in the race. blood centrifuging
Blood is also centrifuged during a doping check. Some cyclists use a substance such as Erythropoietin (EPO) to generate extra red blood cells. These extra red blood cells enable the body to carry more oxygen thus increasing the athlete’s endurance. There is also a health risk, as the blood becomes thicker therefore increasing the risk of having a heart attack.
blood plasma white blood cells red blood cells
FIG 1.36 Centrifuging blood.
36
1.4
Types of mixtures
residue
filtrate
FIG 1.37 Filtration of a suspension.
A suspension can be separated by sedimentation and by filtration. The filtrate (the liquid) passes through the filter and the residue (the solid matter) remains behind on the filter.
Emulsion, foam, smoke and aerosol
Understanding
An example of a foam is polystyrene foam packaging used for electronic components. Polystyrene foam is very light and flexible. It is a mixture which consists mostly of gas: here small gas bubbles are contained in a plastic (see Section 4.4). With shaving foam, hair mousse and the frothy head on a glass of beer gas bubbles are contained in a liquid. The head on beer does not last long; after a short time the gas disperses into the surrounding air and the liquid falls downwards. The foam collapses and the beer is then flat. An emulsion is a cloudy mixture of two liquids. An emulsifier keeps the droplets of the two liquids mixed together. Foam consists of gas bubbles contained in a solid or a liquid. Smoke is a mixture which often arises during a fire. With smoke there are solid particles of matter floating in the air, for example soot particles. You cannot see through a thick cloud of smoke. You also cannot see through the white cloud from a cooling tower of a factory. This type of cloud consists of small water droplets floating in the air. It is therefore not smoke. This type of mixture is called an aerosol. Hairspray and deodorant also form aerosols when you use them.
Activity 16, page 42. When you put water and oil together and shake them, an opaque mixture is formed. This cloudy mixture of two liquids is called an emulsion. If you leave this emulsion to stand the oil will float on the water again: these liquids separate by themselves. Mayonnaise, low fat margarine and hand cream are emulsions of oil and water, but these emulsions are stable. They do not separate because an agent is added to keep the oil and water mixed. This agent is called an emulsifier. The egg yolk is the emulsifier in mayonnaise. If you have greasy hands you use an emulsifier to clean them, that is, soap. It is almost impossible to wash oil and grease from your hands without soap. Soap ensures that these substances mix with the water and are washed away. You also can’t get the washing up clean without soap. Activities 17 and 18, page 43.
Ch1
Chemistry and substances
FIG 1.38 This is an aerosol, not smoke!
Smoke consists of floating solid particles in a gas. An aerosol consists of droplets of liquid in a gas.
37
Understanding
Mixtures and molecules
As shown in Section 1.2, the properties of a substance are determined by the molecules which make up that substance. This is also true for mixtures, even though they contain more than one type of molecule. Figure 1.39 shows a model of sugar in water. The sugar molecules are separate. The solution is clear, so the separate sugar molecules are so small that light passes between them.
Mayonnaise is an emulsion of oil in vinegar. The oil is not thoroughly mixed with the vinegar. Instead droplets of oil are suspended in the vinegar (see figure 1.40, right). The oil molecules form such large drops that they stop light, so an emulsion is cloudy. Oil and vinegar would quickly separate without an emulsifier. The emulsifier molecules bind both oil molecules and molecules in the vinegar. This prevents the oil droplets from flowing together. In an emulsion the molecules are not thoroughly mixed. Molecules of emulsifier bind to molecules of both liquids.
FIG 1.39 Diagram of a model of a solution
The individual molecules also pass through the holes in a filter. Therefore a solution cannot be separated by filtration. In a suspension of cornflour in water, for example, the solid substance is not dissolved: the suspensions consist of granules in water (see figure 1.40, left).
Oil and water can be mixed using soap. Soap molecules are long with a hydrophilic head. This means that it mixes well with water. The tail of a soap molecule is hydrophobic, which means that it mixes poorly with water but well with oil and fat. When you combine greasy plates or hands with water and soap, the hydrophilic tails of the soap molecules bind to the fat molecules and the hydrophilic heads bind to the water molecules. When you then scrub the plates or rub your hands together the grease comes away. The soap molecules ensure that the microscopically small droplets of fat stay floating in the water and can be washed away. soap molecule
FIG 1.40 Model diagrams of a suspension (left) and an emulsion (right)
hydrophilic head
hydrophobic tail
The suspension is cloudy, as the cornflour grains are so big that they stop the light. A grain (made up of a vast number of molecules) is too big to pass through the holes in a filter. This difference in particle size means that a suspension can be separated by filtration. You don’t need a molecular model to explain precipitation. The solid substance has a higher density than water, so the particles gradually sink to the bottom. In a solution the molecules of the dissolved substance are separate from each other. In a suspension each particle of the solid substance is made up of a vast number of molecules.
38
FIG 1.41 S oap molecules (see model) mix fat droplets (yellow) with water (blue).
Molecules of emulsifier have a hydrophilic part which binds to water and a hydrophobic part which binds to oil or fat.
1.4
Types of mixtures
Questions: Understanding 40 Use an example to show if the following are properties
of a solution or a suspension. a Is always clear and sometimes coloured. b Can be separated by filtration. c Separates after a time.
Understanding
a b c
45 a Draw a model of a dilute sugar solution and of a concentrated sugar solution.
b Explain why you cannot dissolve an unlimited
41 A receipt for lunch is given below. For each item write down if it is a solution, suspension, emulsion or foam.
Which type of mixture is shown here? Which other type of mixture consists of a liquid and a gas? Draw a model of the mixture given in question b.
amount of sugar in water, using the concept of molecules.
46 In places with high air pollution people sometimes hold a Cafe-B
rown’ r ‘The C
e
ge juic ezed oran
€ 3,00 € 2,00 € 3,50 € 3,50
ue Freshly sqwater Mineral getable soup Clear ve soup Split pea ead € 3,00 French br m cheese € 4,00 with crea mini-pancakes € 2,50 of Portion olate € 0,50 Hot choc cream € 2,00 Whipped -------Tea € 24,00 To t a l
FIG 1.42
42 In a laboratory experiment you filter a mixture of chalk,
sand, salt and water. a What does the residue consist of? b What does the filtrate consist of?
43 You can extinguish a fire using a foam extinguisher or
a powder extinguisher. A powder extinguisher is a fire extinguisher that sprays out a fine powder. A gas in the cylinder forces the powder out. a What type of mixture leaves the powder extinguisher: a solution, a suspension, smoke or an aerosol? b Which types of substances are contained in a fire extinguisher that generates foam?
44 Figure 1.43 shows a model of a mixture of a liquid and
a gas.
a handkerchief over their mouths. a Explain if a handkerchief helps protect from harmful smoke. Use a model drawing to illustrate your answer. b Explain if a handkerchief helps protect from harmful gases. Use a model drawing to illustrate your answer.
47 Milk is a mixture of water, fat, protein and various vitamins and minerals, amongst other things. a What type of mixture is milk? b Give an explanation for the white colour of milk. Cow’s milk contains approximately 4% fat. Part of the fat is separated from the milk in the factory by centrifuging. This is how half-fat and low fat milk are made. The fat is used to make butter or cream. c Why doesn’t the fat automatically float on top of the milk? d Draw models of full fat and low fat milk.
48 Various types of skin-care products are available,
many of which are emulsions of oil and water. Hand cream is oil droplets in water, while night cream is water droplets in oil. Both products contain an emulsifier, for example soap. a Draw models of hand cream and night cream. b Which cream feels more greasy? c In the model drawings for a show the position of the soap molecules between the water and oil. Draw the soap molecules as pin-like molecules.
FIG 1.43
Ch1
Chemistry and substances
39
Knowing more
Gel Activity 19, page 43. Hair gel can be used to make your hair stand up in spikes. Hair gel is actually a rather strange mixture: it is clear, but not liquid. What is the secret of molecules of hair gel?
water molecule gel-forming molecule
FIG 1.45 Model drawing of a gel
Composites
Fishing rods and skis are very flexible as well as extremely strong. They are made from a very special mixture of the plastic polyester (Section 4.4) layered with glass fibre mats. Hockey sticks and tennis racket frames are also mixtures of plastic and fibres, but here the fibres are made of carbon and the mixture is known as carbon fibre composite. These types of materials, where the substances are arranged regularly throughout the mixture, are called composites.
glass fibre aluminium
FIG 1.44 Gel is clear, but not liquid.
Hair gel is a syrupy mixture consisting of two substances, gel and water, that are thoroughly mixed. There are therefore also two types of molecules: water molecules and gel-forming molecules. The gel-forming molecules are stretched out. They form a type of net which traps the water molecules so they can no longer move freely. This means that hair gel is an unusual solution, as it is clear but it is not a liquid. Gels are used in other applications as well as hair styling, for example jelly (a dessert) and soft contact lenses.
40
FIG 1.46 The layered plastic Glare®
Most composites are made of fibres in a plastic, but Glare® (Glass Laminate Aluminium Reinforced Epoxy) is an exception. This material was developed at the Technical University (TU) in Delft. Glare® consists of thin layers of aluminium bonded to glass fibres. It is lighter than aluminium and stronger than steel. Another important property is that it tolerates damage. The glass fibre layers prevent a crack in the aluminium from getting bigger. These properties make Glare® very suitable for aeroplanes. The Airbus A380, the largest passenger aeroplane in the world, is mostly made from Glare®.
1.4
Types of mixtures
Knowing more
Fillings Cavities in teeth were once filled with dental amalgam, which is a silver-coloured mixture of metals. Amalgam is strong, easy to use and relatively cheap, but it does have some disadvantages. It contains mercury, which is toxic, and when the filling is put in place a small amount of mercury vapour is released. This is particularly a problem for the dentist who works with this material every day. Sometimes healthy tooth has to be drilled out to give an amalgam filling enough solidity. In addition many people don’t like the colour of these fillings.
Nowadays most cavities are filled with composite material in the same colour as the tooth, so you hardly notice that someone has a filling. A composite filling is made of small grains of glass or quartz (the filling material) mixed with polymer resin (the matrix). The glass or quartz provides rigidity, while the resin is a syrupy liquid which enables the dentist to apply the composite to the hole. The resin inside the tooth must then be cured. Applying the composite filling must sometimes be done layer by layer and therefore takes time. Another disadvantage of a composite filling is shrinkage, which can result in a gap between the filling and the tooth. Food and bacteria can enter this gap and cause a new cavity. Chemists are trying to develop new composites which are rigid, quick drying and have minimal shrinkage.
FIG 1.47 Amalgam fillings (left) and composite fillings (right)
Questions: Knowing more
51 Glare® combines aluminium and glass fibres to make a material which has the properties of both materials. It is often used in aeroplanes. a Which property of aluminium is used in Glare®? b Which property of glass fibre is used in Glare®? c Think of another application of Glare®.
49 What is the purpose of the gel-forming molecules in nappies?
50 Aerogel is an extremely light material which is a poor
conductor of heat. It is used as an insulating material in aerospace applications. a What does the prefix ‘aero’ in aerogel mean? b What could the main ingredient of aerogel be? c Draw a molecular model of a piece of aerogel.
52 Read the information above about fillings again and answer the following questions. a Name two advantages and two disadvantages of composite fillings. b Draw a molecular model of a composite filling. Show the different components clearly. c Name two material properties that the filling material of a composite filling must have. d Name two material properties that the matrix of a composite filling must have.
FIG 1.48 The composite material Glare® is used in this Airbus A380.
Ch1
Chemistry and substances
41
Experimenting
Activity 15 Dissolving and filtration
What to do
You will investigate if iron chloride and iron oxide dissolve in water. You will then filter both mixtures.
• •
You will need • • • • • •
spatula (yellow) iron chloride and iron oxide two funnels two filter papers rack with test tubes siphon bottle with water
A
B
C
• • •
D
FIG 1.49
Put a spatula-tip of iron chloride in a test tube. Add a couple of millilitres of water and shake the mixture for a time. Describe the mixture obtained. Do the same as before now using a spatula-tip of iron oxide in another test tube. Fold two filter papers as shown in figure 1.49. Put each filter into a funnel. Squeeze a small amount of water onto the folded edges so that the filters stay in place and put the funnels into two empty test tubes. Filter both mixtures. Describe the filtrate and the residue in each case.
Questions a Which substance gives a solution in water? b Which substance gives a suspension in water? c From which observation(s) can you deduce which
mixture can be separated by filtration and which cannot?
Activity 16 Water and soap Soap affects the properties of water. This means that you can wash better using soap and water.
You will need • • • • • • • • •
coloured oil liquid soap rack with test tubes two test tube bungs siphon bottle with water two small glass beakers two drawing pins piece of denim fabric pipettes
What to do • Put a few millilitres of water and a few drops of coloured oil into two test tubes. • Add a small amount of liquid soap to one test tube. • Shake both test tubes well for a while. Describe the appearance of the mixtures immediately after shaking.
42
• Leave the test tubes to stand for a couple of minutes. What difference do you see? • Fill two small glass beakers with water. Add a small amount of soap to one beaker and mix well. • Try to get a drawing pin to float on the surface of the water. • Also try to get a drawing pin to float on the water with soap. • Using a pipette carefully place one drop of water onto the denim fabric. Repeat with a drop of soapy water.
Questions a What does the soap do when oil and water are mixed? The soap molecules also decrease the surface tension of the water. b How is this shown in the experiment with the drawing pin? c What is the advantage of decreasing the surface tension when washing clothes?
1.4
Types of mixtures
Experimenting
Activity 17 Solution of polystyrene foam (demonstration) In this experiment you will investigate if you can dissolve polystyrene foam.
You will need • • •
100 mL small glass beaker acetone and polystyrene foam 20 mL or 50 mL measuring cylinder
What to do • • •
Half fill the beaker with tap water. Push two pieces of polystyrene foam under water. Look at the polystyrene foam and the water level.
•
Now pour the water away, remove the polystyrene foam and put 20 mL acetone into the beaker. • See how many pieces of polystyrene foam you can dissolve in the acetone. Also observe the level of the liquid. Environment: do not put experimental waste in the sink! Hand it in to your teacher.
Questions a Explain if you expected this result. b Explain why the liquid level rises less during the
c
second experiment than during the first experiment. Explain whether the polystyrene foam melts or dissolves.
Activity 18 Making meringues Your teacher will tell you to do this at school or at home.
• •
You will need • • • • •
bowl, whisk and spoon one egg white 50 g icing sugar and pinch of salt piping bag and baking paper oven
• •
Add a pinch of salt. Add the icing sugar a spoonful at a time while whisking. When the last spoonful of icing sugar has been added continue to whisk for a short time. Put the meringue mixture in the piping bag. Pipe small rosettes of mixture onto baking paper on a baking tray. Put the baking tray in the centre of the oven and let the meringues dry for 30 minutes. If your meringues have been a success: Enjoy!
What to do
Question
• •
What happens to the molecules in the egg white when the meringues are in the oven? Hint: think about heating an egg.
Heat the oven to 125 °C. Place the egg white in a (very clean) bowl.
Activity 19 Testing nappies
What to do
A baby’s bottom stays dry when wearing a nappy because disposable nappies contain a gel-forming substance. You will investigate how well this substance binds water.
• •
You will need • • • •
weighing scale 250 mL glass beaker disposable nappy siphon bottle with water
• •
Determine the mass of the beaker. Tear the disposable nappy open, remove the gel-forming material and weigh out 2,5 g of this into the beaker. Add water in small amounts until the gel-forming substance will not absorb any more water. Determine the mass of the beaker with saturated gel.
Questions a Calculate how many grams of water the gel-forming substance has absorbed.
b How many times the original mass of the gel-forming substance is this?
Ch1
Chemistry and substances
43
Concluding
Application assignments
Concluding tasks 1 Summary Read the sentences that summarise the theory in the yellow boxes. If there is anything you don’t quite understand read the accompanying explanation in the book.
The following application assignments are available on the Impact website: • Hair-styling products • Iron content of groundwater • Removal of pollutants in glass recycling
2 Key terms test
Test yourself
Take the Key terms test on the Impact website or on your school network.
1 3 The experiments
For each experiment write down the research question, the most important observations and the accompanying conclusion.
4 Class test with true or false questions a Divide into groups of two, three or four students.
Chemistry in the kitchen Explain in which cases a chemical reaction takes place. Make a salad dressing from oil and vinegar. Knead flour, salt and yeast into a dough. Leave dough to rise in a warm place. Boil an egg. Whip cream. Fry chips in a chip pan.
a b c d e f
Each group chooses one of the four sections.
b Everyone thinks of two true or false questions about
2 Making pancakes
the chosen section. c Check that the other members of your group can answer the questions. If a question is too difficult it is discarded. d The questions are collected and the test can begin.
5 A puzzle Working in pairs you are going to guess a number of words from chapter 1. Read the description and guess the answer. Then write down the required letter from that word. These letters form a word which - hopefully describes what you think of Chemistry! 1 Mixture of a solid substance and a gas (2nd letter) 2 Passes through the filter during filtration (5th letter) 3 Remains behind on the filter during filtration (1st letter) 4 You do this with your senses during an experiment (6th letter) 5 Word for solidified water (3rd letter) 6 Room where you do experiments (1st letter) 7 If your clothes are on fire you must be wrapped in this (2nd letter) 8 The amount of a substance in a solution (2nd letter) 9 Cloudy mixture of a solid in a liquid (2nd and 3rd letters)
44
For each step say which is an action (A), which is an observation (O) and which is a conclusion (C). a We put the flour into a bowl and beat in milk and a couple of eggs. b The mixture was a cloudy liquid. c If the mixture is left to stand, solid particles sink to the bottom. d The batter is a suspension. e We heated a piece of butter in the frying pan. f The butter melted and turned brown. g The pan was then hot enough. h We put a spoonful of batter in the pan. i The batter turned into a solid substance (the pancake). j A chemical reaction took place while frying the pancakes.
3 Substance property?
For each of the ten terms given below say if it is a substance property or not. a Odour b Colour c Phase at room temperature d Density e Temperature f Electrical conductivity g Flavour h Mass i Melting point j Solubility
Concluding
air vent ‘open’ gas inlet ‘open’
air vent ‘closed’ gas inlet ‘half open’
1
2
air vent ‘half open’ gas inlet ‘half open’
3
FIG 1.50
7 Breathing
Three drawings of the cross-section of a lab burner are given above. For each drawing give the type of flame you would expect to see.
When sitting calmly you inhale approximately 1,5 dm3 of air with each breath. Air contains 21% oxygen by volume. The exhaled air contains 16% oxygen by volume. a How many cm³ oxygen do you inhale with each breath? b How many cm³ oxygen do you exhale with each breath? You can assume that all of the oxygen that remains in your body enters your bloodstream. c How many cm3 oxygen enters your bloodstream from one breath of air?
temperature (oC)
4 The lab burner
100 90 80 70 60 50 40 30 20 10 0
0
1
2
3
4
5
6
7
8
9 10
time (min) FIG 1.51
5 Pure substance or mixture? Figure 1.51 shows a graph of a substance during melting. Study the graph and answer the following questions. a Is this a pure substance or a mixture? How can you deduce this from the graph? b Using the graph determine the time taken for the substance to melt. c Read the melting point or melting range from the graph.
6 Alcohol A 0,75 L bottle of wine contains 12% vol alcohol. The density of alcohol is 0,80 g/mL. Calculate how many grams of alcohol are consumed by someone who drinks two bottles of this wine.
8 Mixtures Match the following substances with the appropriate type of mixture. A Tea 1 Suspension B Paint 2 Emulsion C Milk 3 Solution D Pepper spray 4 Foam E Chocolate mousse 5 Aerosol
9 Salt extraction Charlie and Imogen want to extract salt from sea water. Sea water contains 30 g dissolved salt per litre. They have 20 mL sea water. It is slightly cloudy due to small particles of sediment floating in the water. They are going to filter the sea water first and then evaporate the filtrate. a Draw a model of this sea water. Show the salt particles and the sediment particles separately. b Explain how the salt and silt are separated using filtration. c Calculate the maximum amount of salt in grams that they can extract in this experiment.
Ch1
Chemistry and substances
You can find a Chapter test on www.impact-online.nl.
45
y
tr s i m
Che
3
o hav o vw
Physics havo/vwo year 3
ma ads kers ek a Ho er H me Pet Heut den mp n Tom hel va olenka Mic am M j Mir slator n a Tr ie Cox o R s or r t Edi ĂŠ Broe n Re
Chemistry havo/vwo year 3
Physics and Chemistry havo/vwo year 1-2