MODULE mod7A mod7B mod7C mod7D mod7E mod7F mod7G mod7H mod7I mod7J mod7K mod7L mod8A mod8B mod8C mod8D mod8E mod8F mod8G mod8H mod8I mod8J mod8K mod8L mod9A mod9B mod9C mod9D mod9E mod9F mod9G mod9H mod9I mod9J mod9K mod9L 9ha1
9Ha1 Heating by displacement 1
How much energy is produced in displacement reactions?
A displacement reaction happens when a metal such as zinc is put into a solution containing the salt of a less reactive metal, such as copper sulphate solution. The reaction produces energy. You can test copper, aluminium, lead, zinc, iron and magnesium to find out which metals will produce the most energy.
Prediction
1 a Which metal do you think will produce the most energy when you put it into copper sulphate solution?
b Explain why you chose that metal.
Apparatus
- Boiling tubes - Copper sulphate solution
- Different metals - Thermometer
- Measuring cylinder - Stopclock
- Spatula - Eye protection
Wear eye protection.
Method
1 Copy the table below into your book.
2 Measure 10 cm3 of copper sulphate solution and put it into a boiling tube.
3 Use the thermometer to find the temperature of the solution. Write the temperature in your table.
4 Put a spatula of zinc turnings into the copper sulphate solution. Start the stopclock.
5 After 2 minutes record the temperature of the solution. Write the temperature in your table.
6 Repeat steps 2 to 5 with the other metals.
Recording your results
Metal
Temperature at start (°C)
Temperature at end (°C)
Temperature change (°C)
copper
aluminium
zinc
iron
magnesium
2 Plot your results on a bar chart. Draw the bar for the metal with the highest temperature change first.
Considering your results/conclusions
3 a Which metal gave the biggest temperature change?
b Which metal gave the smallest temperature change?
4 Do your results match your prediction?
5 Try to explain why some metals gave a bigger temperature change than others. You may need to look up the Reactivity Series in a textbook.
Evaluation
6 How did you make sure your test was fair?
7 Is there any way you could improve your experiment?
[ observing, presenting, considering, evaluating ]
9Ha2 Heating by displacement 2
A displacement reaction happens when a metal such as zinc is put into a solution containing the salt of a less reactive metal, such as copper sulphate solution. The reaction produces energy.
You can test different combinations of metals and solutions to find out which combination will produce the most energy.
- Boiling tubes - Thermometer
- Measuring cylinder - Spatula
- Eye protection - Stopclock
- Solutions of copper sulphate, iron chloride, zinc chloride, magnesium sulphate
- Turnings of copper, zinc, magnesium, iron
1 a Which combinations of metals and solutions of metal salts do you think will produce the most energy?
b Which combinations will produce the least energy?
c Explain the reasons for your predictions using scientific ideas. You may need to look up the Reactivity Series.
Planning
2 How will you find out which combination produces the most energy? Write a method for your investigation. You will need to think about these things:
- Which combinations will you try?
- How much of each solution will you use?
- How long will you leave each reaction before you measure the temperature change?
- How will you make sure you are carrying out a fair test?
- Will you need to repeat any readings?
3 Draw a table ready for your results.
4 Show your method to your teacher before you start. Ask your teacher if you need any more apparatus.
5 Record your results in the table, and draw bar charts to show your results. If you have used more than one solution, you will need to draw a different bar chart for each solution.
6 a Which combinations of metals and solutions produced the most energy?
b Write word equations for these reactions.
7 How do your results compare to your predictions?
8 Describe any pattern you can see in your results. Use scientific ideas to explain the pattern.
9 How accurate were your measurements? Explain your answer.
10 Have you got enough results to draw a firm conclusion? Explain the reasons for your answer.
11 How could you improve your experiment if you had time to do it again?
[ planning, observing, presenting, considering, evaluating ]
9Ha3 Energy from reactions
Name _____________________________ Class ____________
This list shows the reactivities of some metals.
If you put a piece of iron into copper sulphate solution, you get iron sulphate and copper metal. This happens because the iron is more reactive than copper. The reaction produces energy, which heats up the solution. If you put copper into iron sulphate solution nothing happens because copper is less reactive than iron.
1 Look at these reactions. Copy them out and finish them off to show what happens. The first two have been done for you.
a copper + lead nitrate solution →
b zinc + lead nitrate solution →
c magnesium + copper sulphate solution →
d iron + lead chloride solution →
e lead + zinc sulphate solution →
f zinc + copper sulphate solution →
2 The amount of energy given out by a displacement reaction depends on the difference in reactivity between the two metals. For instance, reaction f in question 1 will produce more energy than reaction d. Write the reactions in question 1 in order, starting with the reaction that will produce the most energy. You can just use the letters for the reactions.
3 Metals can also be used to produce electrical energy.
a If one electrode is made of copper, which metal should you use for the other electrode to give the highest voltage?
b Which combination of metals do you think will give the highest voltage: copper and lead, or zinc and lead?
c Explain your answer to part b.
[ knowledge ]
9Ha4 Matches
Matches are very useful for lighting candles, gas cookers or fires. Matches that were ignited (lit) by friction were invented by John Walker in 1827. The match heads contained an element called phosphorus that can be set alight by the heat produced by friction.
Modern safety matches will only light if they are rubbed along the special, rough paper on the matchbox. The side of the box is made of powdered glass and red phosphorus. When the match is struck, the red phosphorus catches fire and ignites the head of the match. The head of the match contains potassium chlorate, sulphur, carbon, glue and a colouring. Potassium chlorate is an oxidising agent. This means that it can provide oxygen that will react with other substances. The rest of the matchstick is treated with a special chemical so that it does not burn too quickly.
1 Why are matches safer if they can only be lit using the matchbox?
2 Which of the substances in the match head and the matchbox are elements?
3 a Which three elements do you think are in potassium chlorate? (Hint: Compounds whose names end in '-ate' contain oxygen.)
b If there is one atom of each element in potassium chlorate, what do you think its formula might be?
4 What produces heat when you strike a match?
5 Why do you think that potassium chlorate is used in match heads?
6 a Which elements in the match head burn when the match is lit?
b Write word equations to represent these reactions.
7 When all the chemicals in the match head have been used up the match carries on burning.
a What is burning?
b Why do you think the match blows out more easily when all the chemicals in the match head have been used up?
[ literacy, knowledge ]
9Ha5 Warm it up!
Hand warmers are small bags of chemicals that react when the bag is opened to let the air in. Climbers or walkers sometimes use them if they are out in very cold weather.
Ollie's Outdoor Supplies want to sell a new hand warmer. They wrote this specification and sent it to Charlie's Chemical Company, to see if the company could develop a new hand warmer for them.
Ollie's Outdoor Supplies
Specification - new hand warmer
There is a market need for a new hand warmer, small enough to fit inside an adult's glove. Due to the small size, the hand warmer may not provide heat for as long as other products on the market, but this will be offset by the low cost.
The hand warmer must meet the following specifications:
Maximum size
4 cm × 5 cm × 1 cm
Maximum temperature
45 °C
Time to reach max temperature
1 minute
Time
The heater must maintain a temperature between 40 °C and 45 °C for at least 2 hours.
Packaging
Outer plastic pack, with tab provided so it is easy to open with gloved hands.
Inner pouch that contains all chemicals while allowing air to reach them.
Safety
The chemicals must not be harmful to skin or clothing in case the pouch is damaged.
The chemicals must not harm the environment.
No special methods of disposal must be required for the chemicals in used or unused hand warmers.
Chemical reactions can also be used to heat food. Here is an advert for a special tin of food that can heat itself!
Self-heating stew!
No cookers! No mess!
Just pull the tab and your meal is hot and ready to eat in 2 minutes!
Pulling the tab lets air into our special pack of chemicals which produce enough heat to warm your food through.
Only £1.50 per can.
1 The specification for the hand warmer and the advert for the self-heating stew are written in very different styles. Write down the differences between the two pieces of text, and why you think they are written differently. You need to think about:
- who is going to read them
- what the text is trying to do
- how much information is provided.
2 Look at the specification for the hand warmer. Write an advert for the hand warmer that could go into a walking magazine. If you have time, illustrate your advert and use colour to make it look attractive.
3 Write a specification for the self-heating stew, or a similar product that uses a chemical reaction to provide heat.
4 Not all hand warmers use the same chemicals, and some hand warmers do not use chemical reactions at all (although they do have chemicals in them). Find out about other types of hand warmer and how they work.
[ literacy, research ]
9Ha6 Carbon monoxide
When natural gas or other hydrocarbon fuels are burned, the products are normally carbon dioxide (CO2) and water. However, if gas fires or heaters do not get enough oxygen, carbon monoxide (CO), soot (carbon) and water can be produced instead. This can happen if the heater is not installed or maintained properly. Carbon monoxide is a poisonous gas, and kills around 30 people every year in the UK. It is particularly dangerous because you cannot see it, smell it or taste it.
All the cells in your body need oxygen. It is carried in the blood by a substance called haemoglobin (pronounced 'hee-mo-glow-bin'), which is found in the red blood cells. If you breathe in carbon monoxide it combines with the haemoglobin to form a compound called carboxyhaemoglobin. Carboxyhaemoglobin cannot carry oxygen around your body. The more carbon monoxide you breathe, the less oxygen can get around your body, and eventually you suffocate. Once carbon monoxide has combined with haemoglobin, it takes a long time for the chemical to return to normal. After you stop breathing in carbon monoxide, it will take 5 hours for the amount of carboxyhaemoglobin to halve.
The symptoms of carbon monoxide poisoning are headaches, fatigue, nausea and dizziness, which get worse as you breathe more of the gas. If you are exposed to the gas for a long time (or too high concentrations of the gas) you could lose consciousness and die.
1 Write word and symbol equations to show what happens when methane (CH4) burns:
a in plenty of air
b when there isn't enough air.
2 How can you tell from the formulae that carbon dioxide and carbon monoxide probably have different properties?
3 What might you see above a heater producing carbon monoxide? (Hint: Look at the other products of the reaction.)
4 What are the symptoms of carbon monoxide poisoning?
5 Explain why carbon monoxide is poisonous.
6 Find out how carbon monoxide can be detected, and ways of preventing poisoning. Use your findings to produce a poster or leaflet that could be given to people to help them to make sure their house is safe.
[ literacy, knowledge, research ]
9Hb1 Using chemical reactions
Chemical reactions can be used as energy resources.
Chemical reactions are used to make new materials.
Chemical reactions are important in plants and animals.
carbon dioxide + water (+ energy) → glucose + oxygen
combustion
iron + copper sulphate → copper + iron sulphate
respiration
CH4 + 2O2 → CO2 + 2H2O
Fertilisers can be made using natural gas and nitrogen from the air.
glucose + oxygen → carbon dioxide + water (+ energy)
enzymes starch → sugars
hydrogen + oxygen → water (+ energy)
Two different metals put into acid can produce an electrical voltage.
Plastics are made using chemicals obtained from oil.
photosynthesis
There are 1400 kJ of energy in a plate of pasta.
methane + oxygen → carbon dioxide + water (+ energy)
A displacement reaction can be used to get iron from iron oxide that is found in rocks.
Burning is an oxidation reaction.
9Hb2 Painkillers 1
In South America, local people sometimes chew the leaves of the coca bush. This has been done for at least 1500 years. Chewing the leaves makes them feel happy, alert and full of energy. It also makes their mouths feel numb.
In 1863 a chemist from Corsica called Angelo Mariani started to sell a drink made from coca and wine. This drink could cure headaches. It was an anaesthetic (painkiller). In 1860 a German chemist called Albert Niemann extracted a chemical called cocaine from coca leaves. Cocaine is the chemical in the leaves that is mainly responsible for the painkilling effects. Later, a scientist called Carl Koller was trying to find a drug that would stop pain during eye surgery. He tested cocaine on frogs, rabbits and dogs, and then tested it on himself. He found that he could make a dent in his eye with the head of a pin without feeling it at all.
Cocaine is not a very useful anaesthetic because it also damages the brain. Chemists tried experiments with cocaine and other extracts from plants, and managed to make other compounds. They tested these compounds, and some of them were good anaesthetics that did not damage the brain. Today there are lots of different anaesthetics that doctors and dentists can use to stop pain.
1 The table shows some of the stages in developing new drugs. Fill in the right-hand column to show who carried out each stage.
Stage
Who did it?
noticing that plants had an effect on the body
using the plants to make a medicine
finding the chemical in the plant that had the effect
experimenting with the chemical to find out how good it was, and if it had other, bad effects on the body
2 What is an anaesthetic? _______________________________________________________
__________________________________________________________________________
3 What bad effect does cocaine have? ______________________________________________
4 How did chemists try to find better anaesthetics? __________________________________
9Hb3 Painkillers 2
In South America, local people sometimes chew the leaves of the coca bush. This has been done for at least 1500 years. Chewing the leaves makes them feel happy, alert and full of energy. It also makes their mouths feel numb. Coca leaves have an anaesthetic (pain killing) effect.
In 1863 a chemist from Corsica called Angelo Mariani started to sell a drink made from coca and wine. This drink could cure headaches. In the USA, John Pemberton invented a drink made from extracts of coca leaves and extracts from the seeds of a tree called Cola nitida. In 1886 alcohol was banned in the USA, so they used sugar syrup instead of wine, and called the drink Coca-ColaTM. Today there is no coca in Coca-ColaTM.
In 1860, a German chemist called Albert Niemann extracted a chemical called cocaine from coca leaves. Cocaine is the chemical in the leaves that is mainly responsible for the painkilling effects. Later, a scientist called Carl Koller was trying to find a drug that would stop pain during eye surgery. He tested cocaine on frogs, rabbits and dogs, and then tested it on himself. He found that he could make a dent in his eye with the head of a pin without feeling it at all.
Cocaine is not a very useful anaesthetic because it also damages the brain. Chemists tried experiments with cocaine and other extracts from plants, and managed to synthesise (make) other, similar compounds. They tested these compounds, and some of them were good anaesthetics that did not have harmful side-effects. Today there are lots of different anaesthetics that doctors and dentists can use to stop pain.
1 What is an anaesthetic?
2 Who first noticed the anaesthetic effects of coca leaves?
3 a What is the chemical in coca leaves that causes the anaesthetic effect?
b Who first extracted this chemical?
4 Why did the drink Coca-ColaTM get its name?
5 What do you think 'side-effects' are?
6 There were several stages in the development of modern anaesthetics. Put these statements in order to make a flow chart to show the stages. Write names and dates with each stage if you can.
- Finding the chemical in the plant that had the effect.
- Noticing that plants had a useful effect.
- Making and selling anaesthetics for doctors and dentists to use.
- Testing the chemical to see if it had a useful effect.
- Testing other chemicals to find out about their anaesthetic effects and side-effects.
- Using plants to make medicines.
- Finding or making other, similar chemicals.
9Hb4 Tasty reactions
If you go into a sweet shop or a supermarket, you will probably recognise most of the snacks or sweets on sale. Sometimes you may notice a new kind of sweet or snack. Who invents new foods, and how do they do it?
The companies who make foods need to make a profit. If some of their foods are not selling well they may decide that they need a new product to help them to make more money. For instance, they may decide that people might like to eat chicken-flavoured cereal bars.
Food companies have research kitchens where food scientists try out new recipes. They would try different recipes for the new cereal bars. They would pick a few of the ones that they thought were the best, and then they would hold a focus group. At a focus group the company gives people the different cereal bars to taste, and asks them which ones they like. If the focus group doesn't like any of them, they have to go back to the kitchens and try out more recipes!
When they have found a recipe that people like, they have to make sure that it can be mixed and baked using factory machinery. They also need to find the cheapest ingredients that still give a good taste, and make sure that the cereal bar will keep for a long time in its wrapper. The company's marketing personnel also need to make sure that the new snack will sell. They need to design an attractive wrapper for it, and they may decide to have an advertising campaign in newspapers or magazines, or even on the TV or radio. They also have to persuade supermarkets to sell the product for them.
1 Why might a food company decide that a new product is needed?
2 What happens in a research kitchen?
3 a What is a focus group?
b Why do companies designing new products hold focus groups?
4 What happens if the people at the focus group do not like any of the new products they are shown?
5 If the people at the focus group choose the best product, what has to happen before the product can be sold to supermarkets?
6 How does the company try to persuade people to buy its new product?
7 Imagine you are in charge of a company that has decided to make fruit-flavoured biscuits. Write a list of instructions for your staff to tell them what to do to develop the new biscuits.
[ knowledge, literacy ]
9Hb5 A cure for flu
Influenza ('the flu') is a disease caused by a virus. Viruses cannot be killed using antibiotics or many other kinds of drug. A patient with the flu will have a high temperature and aches and pains in the muscles. For a fit adult, flu is a nuisance but is not usually dangerous. However, it can be fatal for elderly people or small children whose immune systems may not be working very well. The flu virus mutates (changes) very quickly, and some strains of the virus are more dangerous than others. Between 1918 and 1919 a flu virus (called Spanish flu) caused 20 million deaths world-wide.
Vaccines are made from dead microbes, and help the body's immune system to create antibodies to fight a disease. Flu can be prevented with vaccines, but the vaccine will not work if the virus has mutated. One way of trying to make a new drug to prevent flu is to study the virus itself.
A flu virus has two kinds of molecules sticking out from it. One kind attaches the virus to the cells it attacks. The virus gets inside cells and replicates (reproduces). The second kind of molecule is an enzyme called sialidase which helps the viruses break out of the cell so they can go on to infect more cells.
The part of an enzyme that makes it work is called the active site, and this has a particular shape that fits the chemicals that it helps to break down. If chemists can find a molecule that fits into this active site and blocks it up, the enzyme will not be able to work. They can use the molecule to make a drug that will stop the flu virus breaking out and infecting other cells.
Chemists tried many molecules, but could not find one that was effective. In the 1980s, a group of Australian chemists used X-rays to study sialidase, and investigated the shape of the active site. They then built a computer model to represent the shape, and used it to help them to investigate possible molecules that might fit into it. They designed and synthesised new compounds that blocked the enzyme. They tested them on animals, and found that they worked very well.
However, there is still a long way to go before this new chemical can be used. Trials have to be done to make sure it does not have harmful side-effects, and then clinical trials will be carried out to test it on people. It will only be prescribed by doctors if it passes all these tests.
1 Write down the meanings of all the bold words in the text above. You may need to look up some words in a dictionary.
2 Why is it difficult to find a cure for the flu?
3 Which people are in the most danger from flu?
4 Use the information above to draw a flow chart to show the stages in developing a new drug to treat a disease.
5 Find out what the following words mean:
- placebo
- a 'double blind' trial.
9Hc1 Mass in reactions 1
What happens to the mass of chemicals in a reaction?
- Small beakers - Spatula
- Balance - Universal indicator
- Thermometer - Tripod and gauze
- Bunsen burner - Eye protection
- Heatproof mat - Sodium hydroxide solution
- Copper sulphate solution - Sodium chloride
- Hydrochloric acid - Iron filings
- Ice
Carry out the experiments described in the table. Measure the mass of the chemicals before and after each experiment.
Experiment
1st step
2nd step
A
Find the masses of about 20 cm3 of copper sulphate solution and 20 cm3 of sodium hydroxide solution in beakers.
Total mass = _______________ g.
Mix the two chemicals, and find the mass of the mixture and the empty beaker.
B
Put 20 cm3 of hydrochloric acid in a beaker and add a few drops of universal indicator. Put 20 cm3 of sodium hydroxide in another beaker. Measure the temperature of the acid.
Temperature of acid = ______________ °C.
Add sodium hydroxide slowly to the acid until the indicator changes colour. Stir the mixture with the thermometer. Measure the temperature of the mixture. Find the mass of the mixture and any leftover sodium hydroxide.
Temperature of mixture = _____________°C
C
Find the mass of a small beaker full of ice.
Mass = _______________ g.
Heat the ice until it has just melted.
Find the mass of the beaker and the melted ice.
D
Find the mass of 4 spatulas of iron filings and about 20 cm3 of copper sulphate solution.
Add the iron filings to the copper sulphate solution. Stir and leave for a few minutes until you can see a change of colour. Find the mass of the mixture and the empty beaker.
E
Find the mass of some sodium chloride and about 20 cm3 of water.
Add the sodium chloride to the water and stir until it is dissolved.Find the total mass of the solution and the empty beaker.
1 Complete the sentences using words from the box. You may use each word once, more than once or not at all.
When the two chemicals were mixed in experiment A, a ________________ reaction
happened. The mass of the chemicals was ________________ before and after the reaction.
B was a ________________ reaction. The temperature of the chemicals ________________ .
The mass of the reactants was _________________ the mass of the products.
C was a _________________ change. The mass of the ice was the mass of the water.
D was a _________________ reaction. The mass of the reactants was
_________________the mass of the products.
In E, the sodium chloride _________________ in the water. The mass of the chemicals at the
beginning was _________________ the mass of the chemicals at the end.
chemical decreased different different from displacement dissolved
increased melted neutralisation physical the same the same as
2 Complete this sentence using the correct word from the two alternatives.
The mass of chemicals _________________ (does/does not) change in a chemical reaction.
[ observing, considering ]
9Hc2 Mass in reactions 2
- Copper sulphate solution - Iron filings
- Hydrochloric acid - Sodium chloride
1 Carry out the following experiments. Record the masses of the chemicals before and after each change, and write down any other observations.
A Mix approximately 20 cm3 of copper sulphate solution with 20 cm3 of sodium hydroxide solution.
B Put some universal indicator into approximately 20 cm3 of hydrochloric acid. Slowly add sodium hydroxide until the colour changes.
C Heat a small beaker of ice until it has just melted.
D Add some iron filings to copper sulphate solution in a small beaker.
E Add sodium chloride to water.
1 For each change:
- say whether it was a physical change or a chemical reaction
- name the kind of chemical reaction or physical change, if you can
- say whether or not the mass changed.
2 Can you draw a general conclusion from your results?
3 Could you have carried out your experiments more accurately? If so, explain how.
9Hc3 Conservation of mass
1 When carbon burns it combines with oxygen to form carbon dioxide. The diagram shows some carbon atoms reacting with some oxygen molecules.
a Finish the diagram by drawing the correct number of carbon dioxide molecules. One has been done for you.
b Write 'reactants' and 'products' under the correct sides of the diagram.
c 12 g of carbon reacted with 32 g of oxygen. What mass of carbon dioxide was formed? Circle the correct answer.
12 g 24 g 32 g 44 g 64 g
2 This diagram below shows the reaction between marble chips and acid.
This is the word equation for the reaction:
calcium + hydrochloric → calcium + carbon + water
carbonate acid chloride dioxide
a Is carbon dioxide a solid, a liquid or a gas? ____________________________________
b What would you expect the balance to read when the reaction has finished? Circle the correct answer.
179 g 180 g 181 g
c Explain your answer to part b. _____________________________________________
______________________________________________________________________
3 If you heat a piece of copper, it combines with oxygen from the air to form a black layer of copper oxide.
a Write a word equation for this reaction.
b How would the mass of your piece of copper change as you heated it?
c Why would this happen? _________________________________________________
9Hc4 Magnesium oxide 1
Class 9J did an experiment to find out what happened to the mass of magnesium when it was heated. Each person had a different length of magnesium ribbon. They put the magnesium into a crucible and heated it. The lid on the crucible caught most of the smoke, but they had to lift the lid a little bit now and then to let some air in.
Here are their results.
Mass of magnesium (g)
Mass of magnesium oxide (g)
0.10
0.17
0.20
0.33
0.30
0.55
0.40
0.66
0.50
0.83
0.60
0.99
0.70
1.06
0.80
1.33
0.90
1.49
1.00
1.66
1 Write a list of the apparatus each person used.
2 Draw a graph to show the class results. Use axes like these:
3 Draw a line of best fit on your graph (a straight line that goes through most of the points).
4 Two of the results do not fit the pattern. Draw rings around these points on your graph.
5 Use your graph to predict what mass of magnesium oxide would be formed if you heated 0.55 g of magnesium.
6 Why does the magnesium oxide have a greater mass than the magnesium?
[ presenting, considering ]
9Hc5 Magnesium oxide 2
Five people from Class 9J did an experiment to find out what happened to the mass of magnesium when it was heated. Each person had a different length of magnesium ribbon. They put the magnesium into a crucible and heated it. The lid on the crucible caught most of the smoke, but they had to lift the lid a little bit now and then to let some air in.
Mass of crucible = 40 g.
Length of ribbon (cm)
Mass of Mg and crucible (g)
Mass of MgO and crucible (g)
2
40.14
40.25
4
40.28
40.45
6
40.42
40.69
8
40.56
40.83
10
40.70
41.17
1 Draw a table with these headings:
2 Fill in your table using Class 9J's results. (Hint: You need to subtract the mass of the crucible.)
3 Plot a graph to show their results. Put the mass of magnesium used on the horizontal axis. Draw a line of best fit through the points.
4 What mass of magnesium oxide would you expect to get if you heated 0.35 g of magnesium ribbon?
5 One of the results does not fit the pattern.
a Which result does not fit?
b What could have gone wrong in this experiment?
6 Sally suggested that all the experiments should be done again. How would this help to make the results more accurate?
9Hc6 Law of conservation of mass
If you heat a piece of copper in the air, it reacts with oxygen from the air and forms copper oxide. If you find the mass of the metal before and after the reaction, you will find that the mass has increased.
1 Write a word equation to show what happens when copper burns.
2 a How many reactants are there in this reaction?
b What are the reactants?
3 What is the product of this reaction?
4 When you find the mass at the end of the experiment, what chemical are you finding the mass of?
The difference in masses between the mass of the original copper metal and its mass after heating is the mass of the oxygen which has joined onto the copper during the reaction. We can show this on a lever balance:
The atoms have moved about, but there are still the same number after the reaction as there were before. If there are the same atoms at the end as there were at the start, there must be the same total mass, so the lever balance is balanced.
5 Explain why the mass of the copper seems to go up when you heat it in air.
6 Use the same ideas to predict what will happen if magnesium is heated in oxygen.
7 If you heat carbon strongly in air, the mass seems to go down. Why does this happen? (Hint: think about the product of the reaction, and what happens to it.)
9Hc7 Symbol equations for burning
Hydrogen burns to form water. Hydrogen is a gas which is an element, so it only contains hydrogen atoms. Hydrogen normally exists as a moleule of two hydrogen atoms joined together. We write this as H2. Oxygen also normally exists as molecules (O2). Water is two hydrogen atoms joined to one oxygen atom (H2O).
We can draw each atom as if it is a circle, so we can show the reaction in words, in symbols, and by drawing.
But there is a problem here. We started with two oxygen atoms (joined together in one molecule), but only one of these oxygen atoms is in the water. We cannot destroy atoms. So, we must have started with more hydrogen than oxygen. We write the equation like this, to show how many of each kind of atom reacted:
Now we have used up all the atoms we started with. We say that our symbol equation is balanced. The large 2 in front of the H2 shows us that we started with two molecules of hydrogen, and the 2 in front of H2O tells us that we ended up with two molecules of water.
Methane is a fuel made only of atoms of carbon and hydrogen. One molecule of methane contains 1 atom of carbon and 4 atoms of hydrogen joined together. This is rather a lot to write, so we summarise it as CH4. The C stands for 1 carbon atom and the H4 tells us there are 4 hydrogen atoms. We can draw a molecule of methane like this:
1 Methane burns to produce carbon dioxide and water. Write a word equation to show what happens when methane burns.
2 Draw diagrams of the different molecules under your word equation.
3 Count up the atoms of each element on both sides of your drawing. Do you have the same number of each type on each side of the arrow? Add molecules to your drawings until the number of atoms match. (Remember, you cannot change the formula of a molecule, so methane is always CH4, water is always H2O, and so on.)
4 Now write a balanced symbol equation to show what happens in this reaction.
5 Pure carbon can burn. Write a word equation, draw the molecules, and write a balanced symbol equation to show what happens when carbon burns.
6 Magnesium burns to give magnesium oxide, with one atom of magnesium joined to one atom of oxygen (MgO). Write a word equation, draw the molecules, and write a balanced symbol equation to show what happens when magnesium burns.
9Hd1 Reviewing reactions
Neutralisation reactions
copper + oxygen → copper oxide
magnesium + hydrochloric acid → magnesium chloride + hydrogen
HCl + NaOH → NaCl + H2O
glucose + oxygen → carbon dioxide + water
Bubbles form if you put a piece of metal into an acid.
Displacement reactions
C + O2 → CO2
metal + acid → salt + hydrogen
Natural gas burns in air.
Copper turns black if you heat it.
magnesium oxide + sulphuric acid → magnesium sulphate + water
Oxidation reactions
A piece of iron turns brown when it is put into copper sulphate solution.
Mg + H2SO4 → MgSO4 + H2
copper + silver nitrate → copper nitrate + silver
hydrochloric acid + sodium hydroxide → sodium chloride + water
methane + oxygen → carbon dioxide + water
carbon dioxide + water → glucose + oxygen
acid + alkali → salt + water
Zn + CuSO4 → Cu + ZnSO4
9Hd2 Changing ideas 1
Wood is a fuel.
Phlogiston escapes as the wood burns.
Ash is left.
Complete these sentences, using words from the box. You can use the words once, more than once or not at all.
The _________________ theory said that everything contained a substance called phlogiston.
When something _________________ , phlogiston escaped into the _________________.
This theory explained why the _________________ of a piece of wood was less after it had been
burnt. The original _________________ contained the _________________ and phlogiston, and
after burning there was only the ash left so it would have a _________________ mass.
The phlogiston _________________ did not explain why metals gained mass when they were
_________________ .
Lavoisier carried out lots of _________________ by heating substances and carefully
_________________the mass of the reactants and _________________ . He had a new
_________________about burning. He said that about a _________________ of the air is a gas
called oxygen. When things burn they combine with _________________ from the air. Wood loses
_________________ when it burns because one of the products of the reaction is
_________________ dioxide, which escapes into the _________________ .
Most scientists accepted Lavoisier's theory because it _________________ more observations than
the _________________ theory.
air ash bigger burnt carbon experiments explained fifth
heated mass measuring oxygen phlogiston products quarter
smaller theory third wood
9Hd3 Changing ideas 2
Scientists believed in the phlogiston theory for many years. They used the theory to explain observations. For instance, many things like coal lose mass when they burn. The scientists thought that this was because coal had phlogiston in it, and the phlogiston escaped when the coal burnt.
The theory could not explain why metals gained mass when they were heated. Some scientists thought that there might be two kinds of phlogiston, one of which made things lighter instead of heavier. Other scientists did not think this was important. For centuries science had been about thinking about things, not measuring them. Some scientists were beginning to make careful observations and measurements, but at that time not everyone believed that measurements mattered very much.
When Priestley discovered oxygen, he thought it was air with the phlogiston removed. It was Lavoisier who realised that Priestley had discovered a new gas, which he called oxygen. He thought that when something burned, oxygen combined with the burning substance to form a new chemical.
Lavoisier carried out lots of experiments, making careful measurements of the masses of the chemicals he used, and found that his idea worked. The idea that oxygen could combine with other substances even explained why metals gained mass when they were heated in air. Lavoisier showed that this new gas formed about of the air.
1 If you burn a piece of coal, its mass gets less. How does the phlogiston theory explain this?
2 a What observation could not easily be explained by the phlogiston theory?
b How did some scientists try to explain this observation?
3 What was different about the way that Lavoisier did his experiments, compared with many scientists of his time?
4 How did Lavoisier explain the fact that metals gained mass when they were heated in air?
5 Look at the diagram showing Lavoisier's candle experiment.
a Why has the water level risen?
b How did Lavoisier explain the new level of the water in this experiment?
6 Karl Scheele (1742-1786) was a Swedish chemist who discovered oxygen in 1772. Priestley discovered oxygen in 1774. Find out why Priestley is usually given the credit for discovering oxygen.
9Hd4 More about phlogiston
Scientists used the phlogiston theory to explain some of their observations. Now we no longer believe that phlogiston exists, we must be able to explain the observations in a different way. Explain the ideas below in modern terms and, if you can, give the modern names for the substances mentioned and write word equations. The first one has been done for you.
(Hint: A 'calx' is usually an oxide.)
1
3
5
9H Summary Sheets
Using chemistry
Energy from reactions
Hydrocarbon fuels are made from the elements carbon and hydrogen. Coal, oil and natural gas (methane) are all hydrocarbons. When hydrocarbons burn they form carbon dioxide and water, and release heat energy.
If there is not enough oxygen available, carbon monoxide or even soot is produced.
Other kinds of reaction can also be used as energy resources.
- Displacement reactions happen when a metal displaces a less reactive metal from a solution. The reaction gives out heat energy.
- Two different metals put into acid can produce electrical energy.
- Oxidation reactions happen when something reacts with oxygen. Most oxidation reactions give out heat energy.
New materials
Chemical reactions are used to make nearly all the materials around us. Plants make glucose from carbon dioxide and water, using energy from sunlight. Plants make all the chemicals they need using this glucose, together with water and mineral salts. All the chemicals in our bodies are made from the food we eat, by chemical reactions that happen in our cells.
New materials are being developed all the time. Some new materials have better properties than older ones, or are cheaper to make. New foods and drugs are also being developed. Once a new material has been discovered, scientists have to work out how to make it in a factory, and how to make it into new products. New drugs have to be tested to make sure they work and to check that they do not have any harmful effects.
Law of conservation of mass
In a chemical reaction, the mass of the reactants is always the same as the mass of the products. This is because atoms are not created or destroyed in chemical reactions; they are just rearranged into different compounds.
Sometimes the chemicals in a reaction seem to gain or lose mass. If you heat copper it reacts with oxygen from the air to form copper oxide, which has a greater mass than the original copper. However, if you could find the mass of oxygen that had reacted, you would find that the total mass of the reactants (copper and oxygen) was exactly the same as the mass of the product (copper oxide).
When you burn a piece of wood, the ashes that are left have a smaller mass than the wood you started with. This is because one of the products of the reaction is carbon dioxide gas, which has escaped into the air.
Ideas about burning
Oxygen was discovered in 1772, and a few years later a scientist called Antoine Lavoisier suggested that when things burnt they combined with oxygen from the atmosphere. Before then, scientists had believed that the phlogiston theory explained what happened when things burnt.
Phlogiston was a substance that was supposed to be a part of all materials that could burn. Wood, for instance, was thought to be made of ash and phlogiston. When the wood was burnt, the phlogiston escaped into the air and left the ash behind.
The phlogiston theory could explain a lot of observations about burning and other reactions, but it did not explain why some things appeared to gain mass when they reacted. Lavoisier's idea was based on careful measurements and experiments, and explained more observations than the phlogiston theory. Eventually all scientists accepted Lavoisier's idea.
9H Target Sheet
Topic
Targets
Before the unit
I have learned this
I have revised this
9Ha
Understand what fuels are.
Know which chemicals are made when fuels burn.
Know why burning fuels should always be given a good supply of air.
How displacement reactions can be used as energy resources.
9Hb
Know some reactions that happen in living systems.
Know some common materials made using chemical reactions.
Know why new materials are developed.
Know some of the stages in the development of a new product.
9Hc
Know what happens to the mass of the chemicals in a reaction.
Explain why mass seems to be lost in some reactions.
Explain why mass seems to be gained in some reactions.
Know what happens to atoms in a reaction.
9Hd
Know some examples of hydrocarbon fuels.
Know which compounds are formed when hydrocarbons burn.
Know what happens to the mass of chemicals in burning.
Know something about the phlogiston theory.
9H Word Sheets
Word sheets that include new words from the 'Focus on:' pages are available on the Exploring Science website.
9Ha - Energetic reactions
Word
Pronunciation
Meaning
A burning reaction, when a fuel combines with oxygen and releases energy.
displacement
A reaction that occurs when a more reactive metal 'pushes' another metal out of a compound and takes its place.
hydrocarbon
A chemical compound containing only hydrogen and carbon.
oxidation
A reaction that occurs when an element or compound combines with oxygen.
voltage
A way of saying how much energy is transferred by electricity.
9Hb - Making materials/Kevlar
Kevlar
A manufactured fibre that is very strong.
9Hc - A matter of mass
law of conservation
The idea that the total mass of all the reactants in a chemical reaction is the same as of mass the total mass of all the products.
precipitate
pre-sip-it-ate
Insoluble solid produced by mixing two solutions.
9Hd - Burning ideas
calx
A substance like the ash from a fire. Some scientists used to think that all substances were made of a mixture of calx and phlogiston.
evidence
Results of experiments that support or disprove a theory.
phlogiston
flo-jist-on
A substance that was thought to be part of most materials. Phlogiston was thought to be given off when things burnt.
theory
An idea about why something happens that can be tested by carrying out scientific experiments.