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 8fa1
8Fa1 Iron and sulphur 1
Name _____________________________ Class ____________
Test 1: Observation
Apparatus
- Test tubes
- Test tube rack
- One small test tube (ignition tube)
- Ignition tube holder
- Bunsen burner
- Mineral wool
- Cloth or rag
- A magnet
- Eye protection
- Iron
- Sulphur
- A mixture of iron and sulphur
- Heatproof mat
- Tongs
Method
1 Look at iron, sulphur, and the mixture of iron and sulphur.
Recording your results
Write your observations in the table. The first one has been done for you as an example.
Substance
Description
iron
sulphur
iron and sulphur mixture
Test 2: Floating and sinking
2 Collect three test tubes.
3 Fill each one about half full with water
4 Put a spatula of iron into tube 1. Put a spatula of sulphur into tube 2, and a spatula of the mixture into tube 3. Write your observations in the table.
In the table, write down which things float and which sink.
Float or sink?
Test 3: Magnetism test
5 Collect three dry test tubes.
6 Put a spatula of iron into tube 1. Put a spatula of sulphur into tube 2, and a spatula of the mixture into tube 3.
7 Bring a magnet up to each tube.
In the table, write down which substances are attracted to the magnet, and which
are not.
Magnetic or non-magnetic?
Test 4: Making a compound of iron and sulphur
8 Put two spatulas of the iron and sulphur mixture into a small test tube (ignition tube).
9 Put a small piece of mineral wool in the end of the tube. This will help to stop fumes escaping.
10 Heat the tube in a Bunsen flame until you see a red glow inside the tube.
Wear eye protection.
11 Take the tube out of the flame.
12 When the reaction has finished, leave the tube on a heatproof mat to cool.
13 Wrap the tube in a cloth or rag.
14 Break the glass with a pestle or hammer.
15 Use tongs to pick out the pieces of iron sulphide.
16 Carefully place the broken glass in the broken glass bin.
17 Try tests 1 to 3 on the iron sulphide.
Write your results in the table.
Test
Result for iron sulphides
Appearance
Magnetic or not?
Considering your results/conclusions
The compound that you have made is different from the elements.
How can you tell? Write down two ways.
i __________________________________________________________________________
ii __________________________________________________________________________
Complete this word equation for the reaction
iron + _________________________ → _________________________ sulphide
[ observing, considering ]
8Fa2 Iron and sulphur 2
1 Describe the appearance of:
a iron
b sulphur
c the mixture of iron and sulphur.
2 Write your observations in a table.
3 Collect three test tubes, and fill each one about half full with water.
4 Put a spatula of iron into tube 1, a spatula of sulphur into tube 2, and a spatula of the mixture of iron and sulphur into tube 3.
5 Observe whether each substance floats or sinks. Write your observations in a table.
6 Collect three dry test tubes.
7 Put a spatula of iron into tube 1. Put a spatula of sulphur into tube 2, and a spatula of the mixture into tube 3.
8 Bring a magnet up to each tube, and observe which substances are attracted to the magnet, and which are not. Write your observations in a table.
9 Put two spatulas of the iron and sulphur mixture into an ignition tube.
10 Put a small piece of mineral wool in the end of the tube. This will help to stop fumes escaping.
11 Heat the tube in a Bunsen flame until you see a red glow inside the tube.
12 Take the tube out of the flame, and when the reaction has finished, leave the tube on a heatproof mat to cool.
13 Wrap the tube in a cloth or rag. Break the glass with a pestle or hammer.
14 Use tongs to pick out the pieces of iron sulphide. Carefully place the broken glass in the broken glass bin.
15 Try tests 1 to 3 on the iron sulphide.
1 Write your observations in a table.
2 Are each of these substances elements or compounds?
c iron sulphide
3 Write down two ways in which you can tell that the compound formed is a different substance from the elements that make it up.
4 Write a word equation for the reaction between iron and sulphur.
5 The formula for iron sulphide is FeS. Draw a particle diagram that shows that iron sulphide is a solid with equal numbers of iron and sulphur atoms. Your diagram should show at least 20 atoms.
[ observing, presenting, considering ]
8Fa3 Elements and compounds 1
Match up the correct sets of three boxes. You could:
- cut out the boxes and stick them down in sets
- use a key to show which boxes go together.
[ knowledge ]
------------------------------------------------------------------------------------------------------------------------------
A colourless liquid which boils at 100ºC.
Formula:
N2
One atom of carbon joined to two atoms of oxygen.
A colourless gas which turns limewater milky and is taken in by plants during photosynthesis.
O2
Eight atoms of sulphur joined together in a ring.
A poisonous gas that can dissolve in water making an acid.
H2O
Two atoms of oxygen joined together.
The gas which makes up nearly 80% of the air.
CO2
One atom of sulphur joined to two atoms of oxygen.
The gas that is used by animals and plants in aerobic respiration.
S8
Two atoms of hydrogen joined to one atom of oxygen.
A yellow solid that is often found around volcanoes.
SO2
Two atoms of nitrogen joined together.
8Fa4 Elements and compounds 2
Fill in the gaps in the table below.
Name of compound and chemical formula
Description of the compound
Name of the elements in the compound
Description of the elements
water
hydrogen
Gas which burns with a pop.
Gas which makes things burn brighter.
common salt (sodium chloride)
NaCl
Soft grey metal that reacts easily with air and water.
Poisonous green gas used in swimming pools to kill bacteria.
calcium carbonate
CaCO3
Grey metal that reacts with water. Black solid that is found inside pencils.
Black solid that is found inside pencils.
oxygen
Gas that turns limewater milky and that we breathe out.
8Fa5 Elements and compounds 3
Draw up a table with four columns like this. Allow enough space for at least five different compounds.
Complete the table by describing the different chemical compounds, and then comparing them to the elements from which the compound is made.
Choose your examples from the following list, or add others that you might have heard of, or can look up.
- water - sand (silicon oxide) - SiO2
- carbon dioxide - sulphuric acid - H2SO4
- calcium carbonate - CaCO3 - magnesium oxide - MgO
- common salt (sodium chloride) - NaCl - tri-nitro toluene (TNT) - C7H5N3O6
8Fb1 Is there a reaction? 1
- Bunsen burner - Eye protection
- Heatproof mat - Test tube holder
- Test tube rack - Test tubes
- Thermometer - Chemicals
Make sure you are wearing eye protection for all these experiments.
Be especially careful with
the hydrochloric acid and ammonia solution.
Carry out the experiments described below. In each case, you should:
- look carefully at what happens and write down your observations
- decide if a reaction has taken place
- see if any changes are reversed when you stop heating or leave the tube to stand
- decide if a chemical reaction has taken place
- record your results in a table.
Method - experiment 1
Place two spatulas of sugar (sucrose) in a test tube. Heat the tube gently. Leave the hot tube in a rack to cool down.
Method - experiment 2
Fill a test tube about one-quarter full with copper sulphate solution. Add ammonia solution drop by drop to the copper sulphate until the tube is about three-quarters full.
Method - experiment 3
Half fill a test tube with dilute hydrochloric acid. Measure the temperature of the acid. Add a spatula of magnesium carbonate. Leave the tube to stand. Measure the temperature when the reaction has finished.
Method - experiment 4
Put about 2 cm depth of sodium carbonate solution into a test tube. Add an equal volume of iron chloride solution.
Method - experiment 5
Put two spatulas of common salt in a test tube and heat with a roaring Bunsen flame. If no change has occurred after about 3 minutes, take the tube out of the flame and leave it to cool on the heatproof mat.
Method - experiment 6
Put about 3 cm depth of water into a test tube. Measure the temperature of the water. Put a spatula of anyhdrous copper sulphate into another tube. Make sure that this tube is dry. Pour the water into the second tube. Watch what happens and measure the temperature of the solution.
8Fb2 Is there a reaction? 2
1 Follow the instructions on Worksheet 8Fb/1.
2 Write down what happens in the table below.
3 Decide if there has been a reaction or not and make an entry in the table. One has been done for you as an example.
Chemicals
What happened?
Is there a chemical reaction? (ü or û)
copper sulphate and sodium hydroxide
heating sugar
copper sulphate and ammonia
hydrochloric acid andmagnesium carbonate
sodium carbonate and iron chloride
heating salt
water and anhydrous copper sulphate
[ observing ]
8Fb3 Completing a concept map
1 There are five boxes on the concept map numbered 1-5. Find the correct word to go in each box using words from the box below.
atom compounds formula oxygen symbol
2 There are four arrows labelled 6-9. Choose the correct phrase from the box below to go with each arrow.
contain only one type of… to make… are types of…
which join together to make…
3 Write down a phrase which would be correct for arrow number 10.
4 Try to make your own concept map using these words:
reaction substance colour gas
8Fb4 Word equations
1 In each of these equations, say if the underlined chemical is a reactant or a product.
a copper sulphate + sodium hydroxide → copper hydroxide + sodium sulphate
b lead nitrate + magnesium iodide → lead iodide + magnesium nitrate
c copper + potassium → copper + potassium
sulphate carbonate carbonate sulphate
2 Copy and complete the word equations for these reactions.
a iron chloride + sodium hydroxide →
b sodium carbonate + calcium chloride →
c lead nitrate + potassium bromide →
d silver nitrate + magnesium chloride →
3 What chemicals do the letters represent in these equations?
magnesium + copper sulphate → a sulphate + copper
magnesium + b chloride → c chloride + zinc
iron + silver nitrate → d + e nitrate
copper + f g → h nitrate + silver
i + j nitrate → iron k + copper
8Fb5 Writing with light
It is possible to split chemicals up using light as a source of energy instead of heat.
In this case, light is being used to split a chemical up. The chemical in the tube is silver chloride. The tube on the left shows what silver chloride looks like. When it has been left in sunlight, a reaction takes place and silver metal is formed. The tube on the right goes darker because of the metal that is being formed. This reaction is used to take black and white photographs. A thin transparent film is coated with a very thin layer of silver chloride. Where the light strikes the film, you get a reaction. The opaque silver metal which is formed gives a negative image on the film.
After a photograph has been taken, the film has to be developed. It is treated with special chemicals that stop the silver chloride from reacting any more.
1 a What is the name of the compound used to take black and white photos?
b What does this turn into when it is split up by light?
c Write a word equation for this reaction. (Hint: There should be two products on the right-hand side of your equation.)
2 Look at the drawing above.
a Which part of the girl's clothing reflects the most light?
b Why does this part of the girl's clothing look dark on the film?
3 a What is a negative image?
b Explain why you get a negative image when light reacts with silver chloride on the film.
c Find out how you can turn the negative into a postive (normal) print.
[ literacy, knowledge, research ]
8Fc1 What sort of water? 1
How can you tell the difference between different types of water?
You will use three types of water: pure water, sea water and mineral water.
Each one has been given a letter: A, B or C.
You have to try to match the right letter to each type of water.
Test 1: pH test
1 Dip a piece of universal indicator paper into each water sample. What colour does it go?
- Water samples
- Indicator paper
- Watch glasses
- Boiling tubes
- Test tube holder
- Thermometer
2 Write your results in the table.
Water
Colour of indicator paper
pH number
Acid, alkali or neutral
A
B
C
Test 2: Boiling point test
1 Fill a boiling tube about one-quarter full with a sample of water.
2 Adjust the Bunsen so that it is on a gentle blue flame, and turn the gas down so that it is about half on.
3 Place a thermometer in the tube and heat the tube carefully. Move the tube in and out of the flame.
4 Heat the water until it boils and measure the temperature.
5 Write down the boiling point of the water.
Boiling point (°C)
Test 3: Evaporation test
1 Put a little of each water sample onto different watch glasses. Make sure you label each glass so that you know which sample is which.
2 Put the watch glasses in a warm place and leave them while the water evaporates.
3 Draw the results of this experiment in the space below.
Water sample A
Water sample B
Water sample C
For each type of water, say if it is an element, a compound or a mixture. Write your answer in the table below.
Which letter do you think goes with each type of water?
Write your answer in the last column of the table.
Type of water
Element, compound or mixture
Letter
pure water
mineral water
sea water
How do you know which water is which? Give one reason in each case.
I think that pure water was letter _________ because ___________________________________
_______________________________________________________________________________
I think that mineral water was letter _________ because _________________________________
I think that sea water was letter _________ because ____________________________________
8Fc2 What sort of water? 2
In this experiment you will try some tests to tell the difference between different types of water.
You will use four types of water: pure water, tap water, sea water and mineral water.
Each one has been given a letter: A, B, C or D.
- Test each of the water samples with universal indicator paper.
1 Write down your observations in a table which shows:
- the letter of the water sample
- the colour of the indicator
- the pH number
- whether the water is acid, alkali or neutral.
Test 2: Evaporation test
1 Put a little of each water sample onto different watch glasses. Make sure you label each watch glass so that you know which sample is which.
3 What differences would you expect from the different types of water?
Write down your predictions.
4 Go on to Test 3 while you are waiting for the water to evaporate.
2 Draw a diagram or write a sentence to describe the appearance of each sample after the water has evaporated.
Test 3: Boiling point test
Predictions
3 What is the boiling point of pure water?
4 How can this test help you to decide which type of water is which?
2 Wear eye protection. Adjust the Bunsen so that it is on a gentle blue flame, and turn the gas down so that it is about half on.
3 Place a thermometer into the tube and heat the tube carefully until the water boils.
4 Measure the temperature of the boiling water.
5 Record your results in a table.
6 Based on the results of the tests you have carried out, match each water sample to the correct letter. Give your reasons in each case.
7 Use examples from this experiment to explain the difference between elements, mixtures and compounds.
8Fc3 Mixtures
1 Fill in the gaps in these sentences using the words in the brackets.
a Sea water ___________________ (is/is not) a mixture.
b Natural gas ___________________ (is/is not) a mixture.
c Air ___________________ (is/is not) a mixture.
d Aluminium ___________________ (is/is not) a mixture.
e Iron ___________________ (is/is not) a mixture.
2 Fill in the gaps using words from the box.
mixture mixtures oxygen salt sea separate
Most materials are ___________________ made up from different things jumbled up
together. It is usually quite easy to ___________________ the different parts of a mixture.
Air is a ___________________ of different gases. When we breathe our lungs take
___________________ out of the air.
___________________ water is a mixture. It has a chemical called common
___________________ dissolved in it.
3 Find these words in the wordsearch. Show the mixtures in red, the compounds in blue and the elements in pencil.
sea water salt air oxygen iron plastic aluminium
m
n
e
r
a
l
s
d
g
i
P
L
S
T
I
j
x
U
k
c
t
M
o
w
E
u
b
v
N
y
O
p
q
[ knowledge, literacy ]
8Fc4 Element, mixture or compound?
1 Rust is formed when iron objects are left out in the air. The iron reacts with the oxygen in the air to form rust (iron oxide). Rust can be turned back into iron by mixing it with carbon and heating it to a high temperature. I think rust is
______________________ (an element/
a mixture/a compound) _____________________
_________________________________________
________________________________________ .
2 There are a number of different gases in the air. The main ones are nitrogen and oxygen, but there are also small amounts of argon, carbon dioxide and water vapour. I think air is ___________________
(an element/a mixture/a compound)
3 Helium is another gas. There are tiny amounts of helium in the air. Helium does not burn, and will not react with any other chemicals. It cannot be split up by chemical reactions. I think helium is
4 Soil may contain clay or sand. There may also be some stones and humus, such as rotting leaves. Worms make sure that air gets into the soil. I think soil is ______________________ (an element/
5 Sea water is very salty. Rain falls on the land, and tiny amounts of rocks dissolve in the water and get washed into the sea. I think sea water is
______________________ (an element/a mixture/a
compound) because _________________________
6 If you evaporate salty water, common salt is left behind. This is made of two chemical elements, sodium and chlorine. The chemical name for common salt is sodium chloride. I think salt is
8Fc5 Element, mixture or compound? 2
1 Find all the elements in the text below and underline them in red.
2 Underline all the compounds in blue.
3 Use green to show the mixtures.
4 Make a key to show what the colours mean.
5 In your book, explain how you decided if each substance was an element, a compound or a mixture.
A Rust is formed when iron objects are left out in the air. The iron reacts with the oxygen in the air to form rust (iron oxide). Rust can be turned back into iron by mixing it with carbon and heating it to a high temperature.
B There are a number of different gases in the air. The main ones are nitrogen and oxygen, but there are also small amounts of argon, carbon dioxide and water vapour.
C Helium is another gas. There are tiny amounts of helium in the air. Helium does not burn, and will not react with any other chemicals.
D Soil may contain clay or sand. There may also be some stones and humus, such as rotting leaves. Worms make sure that air gets into the soil.
E Sea water is very salty. Rain falls on the land, and tiny amounts of rocks dissolve in the water and get washed into the sea.
F If you evaporate salty water, common salt is left behind. This is made of two chemical elements, sodium and chlorine. The chemical name for common salt is sodium chloride.
8Fc6 Element, mixture or compound? 3
1 The particle diagrams below each represent an element, a mixture or a compound.
For each diagram, say what you think it represents, and give a reason.
D
F
Air is a mixture of gases. Most of the air is nitrogen (formula N2) and oxygen (formula O2). Roughly 1% of the air is argon. This gas exists as single atoms which do not join up. The other important gas in the air is carbon dioxide (formula CO2). Even though it only makes up a small percentage of the air (about 0.04%), it is vital for life as a source of carbon. It also helps to keep the Earth warm enough for life to survive. Air also contains water vapour (formula H2O). The amount of water vapour in the air depends on the weather.
2 a There are five gases named in the passage. Write down whether each one is an element or compound.
b Which gas in the air exists as single atoms? Draw a particle diagram to illustrate the way that the particles are arranged in this gas.
c Name a gas in the air which is an element made from molecules containing two atoms. Draw a particle diagram to illustrate the way that the atoms and molecules are arranged in this gas.
d Name a gas in the air which is a chemical compound. Draw a particle diagram to illustrate the way that the atoms and molecules are arranged in this gas.
e If you had some air which contained a million molecules in total, how many of these molecules would be:
i argon ii carbon dioxide?
[ knowledge, numeracy ]
8Fc7 The ozone layer
Read the passage below and then answer the questions.
Oxygen in the atmosphere is vital for life on earth. The oxygen that we breathe in has the formula O2. High up in the atmosphere, ultraviolet rays from the Sun can convert normal oxygen into ozone. Ozone has the formula O3. This ozone layer helps to stop harmful ultraviolet rays from the Sun reaching the ground. If you get too much ultraviolet radiation you can get badly burned, and could develop skin cancer.
1 a Is air an element, a mixture or a compound? Explain your answer.
b How many atoms are there in a molecule of oxygen? Draw a particle diagram to show this molecule.
c Is oxygen an element, a mixture or a compound? Explain your answer.
d How is ozone different from normal oxygen? Draw a diagram of the ozone molecule.
e Is ozone an element, a mixture or a compound? Explain your answer.
2 Look at this diagram of oxygen molecules.
a How many atoms of oxygen are shown in this diagram?
b How many molecules of ozone could you make from this number of atoms?
c Copy and complete the particle diagram to show what happens when ultra-violet rays convert normal oxygen into ozone.
d Chemists would write the symbols for the oxygen particles in the diagram as 3O2 (g). What is the meaning of the:
i number 3 ii number 2 iii letter (g)?
e Write the symbols for the ozone particles that you have drawn in a similar way.
8Fd1 What's in your orange squash?
All drinks have a label listing the ingredients in them.
A typical orange squash might contain: 60% sugar, 35% water, 5% other chemicals.
These other chemicals will include colours, acids, preservatives, vitamin C and a little protein.
1 This drawing shows what is in your orange squash. Choose one colour for the sugar, another for the water, and a third for the 'other chemicals'. Colour in the diagram with the colours you have chosen.
2 When you make a drink of orange squash, you dilute it with water. In this diagram, imagine that some of the squash has been poured into a glass. Now imagine that you have filled the glass with water. Colour this diagram in to show what is in the diluted squash
3 Complete the sentence below, using your diagram to help you.
In diluted orange squash there is about _____ %
of sugar, _____ % of water and _____ % of
other chemicals.
4 Colour in the circles to show the correct number of particles of sugar and 'other chemicals' in orange squash before you dilute it. Colour in the rest of the circles to show the water. Mix up the circles in this diagram to show that the sugar and water in orange squash are mixed in together, and not in separate layers.
8Fd2 Gases in the air
The air is a mixture made up of many different gases. The main gases are given in the table below, along with the amount of each found in 100 cm3 of dry air. Dry air has no water vapour in it.
Name of gas
Approximate volume of each gas in 100 cm3 of air
nitrogen
78
21
argon
1
carbon dioxide
0.03
1 Use the information in the table to draw a pie chart.
2 Which is the most common gas?
3 Which gas makes up about one-fifth of the air?
4 Why is it so difficult to show the amount of carbon dioxide in the air on your graph?
5 Try to find out what each of the gases in the air can be used for. Write a short paragraph about each one.
[ numeracy, research ]
8Fd3 Research a gas
Choose a gas from this list:
oxygen carbon dioxide nitrogen hydrogen
Your task is to find out as much as you can about your gas.
Present your information in a leaflet or report to help other people learn about the gas.
You should find out about:
- what the gas is used for
- why the gas has these uses
- where the gas is found or obtained from
- how the gas is obtained. (This may be more difficult to find out!)
[ literacy, research ]
8Fd4 Solute calculations
All drinks have a label which gives information on the ingredients in the drink. The ingredients are listed in order of the amounts present, from greatest to least. There is usually a section of nutritional information as well. This tells you how much of each type of chemical there is.
Here is an example of a nutrition label from a bottle of orange squash. Look at the label, and use the information to answer the questions.
1 What is the volume of juice (in cm3) in the whole bottle?
2 How much sugar is there in every 100 cm3 of juice?
3 How much sugar would there be in the whole bottle of juice?
4 What does it say on the label about the volume of one glass of orange squash (one serving)?
5 When you make up the squash, what is the recommended dilution of the squash with water?
6 Imagine you were making one glass of orange drink.
a Calculate the volume of squash that you would need to pour into the glass.
b What volume of water would you need to add?
c Use your answer to calculate how much sugar is in each glass of orange drink.
d Compare your answer to part c with the value on the label - do they agree?
7 The drink contains citric acid and vitamin C. Is there more citric acid, or more vitamin C? How do you know?
8 Estimate the overall percentage of water in the original bottle of drink. Explain your reasoning.
9 Would you recommend this drink as a good source of vitamin C? Explain your reasoning.
8Fe1 Boiling point of water
Does the boiling point of water change if salt is added?
- Beaker - Salt
- Water - Spatula
- Thermometer - Balance
Prediction
1 Do you think the salt will have an effect on the boiling point? Will it make it higher or lower? Why do you think this?
Planning
2 Write a method for your investigation. You need to think about these things:
- How will you measure the boiling point?
- How will you make it a fair test?
- How many experiments will you do?
- How much salt will you add?
- How much water will you use?
- How will you present your results?
Show your plan to your teacher, then carry out your investigation.
3 Put your results in a neat table.
Considering your results/conclusion
4 What have you found out? Was this what you predicted?
Evaluation
5 If you had time to do your investigation again, could you improve it?
Explain your answer.
[ planning, observing, presenting, considering, evaluating ]
8Fe2 Freezing water
In this experiment you will be comparing how pure water and salty water behave when you cool them down.
Predicting
1 What is the freezing point of pure water?
2 Predict the shape of the graph that you will get if you start with water at 5 ºC and cool it down until it has all frozen. (Hint: you may have done a similar experiment with wax before.)
3 How will you be able to use the results of this experiment to tell which of the water samples is pure water and which is salt water?
- Two boiling tubes
- One large beaker
- Crushed ice
- Salt
- Two thermometers
- Stopclock
- Two water samples
1 Place the two boiling tubes in the large beaker and pack crushed ice around the two boiling tubes. Pour salt on to the crushed ice.
2 Put water sample A into one of the boiling tubes, and water sample B into the other. The boiling tubes should be about one-third full.
3 Start timing and measure the temperature of each sample of water at regular intervals. Decide how often you will take the readings. Record your results in a table.
4 Check to see if the water in each tube is totally liquid, starting to freeze, or totally solid. Show this information in the table.
5 Stop taking readings when no further changes are occurring, or when you are confident that you have enough readings to tell the difference between the two samples. You will probably need to take readings for at least 15 minutes.
4 Draw a line graph which shows the temperature on the vertical axis, and the time on the horizontal axis. Use a different colour for each water sample.
5 Describe the shapes of the lines that you have drawn.
6 Which water sample is pure water, and which is salty water? How can you tell?
7 What is the freezing point of the pure water that you used in this experiment? How well does this figure agree with your prediction?
8 On a cold night in the UK, ponds and lakes may freeze over. Rivers freeze less often and the sea has hardly ever been known to freeze. Explain why this is so.
9 What other tests could you have done to show which water sample was pure water, and which was salty water?
[ predicting, observing, presenting, considering ]
8Fe3 Salty ice
In this experiment you will be investigating the effect of adding salt on the melting point of ice.
1 What is the melting point of pure ice?
2 What do you think will happen to the melting point when salt is added?
3 Will the amount of salt make a difference? If so, what difference will it make?
4 How will you measure the temperature? What range of temperatures will you need your thermometer to cover?
5 How much ice might be a sensible amount to use?
6 What form of ice will you use? Would it be best to have one large lump, smaller cubes, crushed ice, or a 'slush' mixture of ice with some water? Explain your choice.
7 Do you need to measure the amount of salt? If so, how will you do it?
8 How much salt do you think you need to add in total? How many different readings are you going to take?
9 Record your results in a suitable table. Don't forget to include the correct units and headings for the table columns.
10 Draw a line graph of your results.
11 Describe what happens when salt is added to ice. Does the amount of salt affect the melting point?
12 Explain how this effect is used on roads and paths in winter.
13 Is it possible to predict what would happen if you kept on adding more and more salt? Explain your answer.
14 Was this a fair test?
15 Are you confident of your conclusions? Explain why, by looking at your graph or results table.
16 Were there any 'odd' results that didn't fit in, or did they all fit with the main trend?
17 Can you suggest any improvements to the apparatus, or to your plan?
8Fe4 Spot the difference
Read each of the statements below.
Decide whether each statement applies to elements, mixtures or compounds.
Some statements could apply to more than one category.
Think about how you could display your information.
Statements
contain chemicals
2
have a definite composition
3
are made up of atoms
4
include air, soil and sea water
5
contain only one type of atom
6
can be represented by a chemical formula
7
include oxygen, iron, sulphur and sodium
8
contain more than one type of atom
9
contain different substances that are not chemically combined
10
can be solids, liquids or gases
11
include water, salt, sugar and carbon dioxide
12
contain molecules
[ knowledge, presenting ]
8Fe5 Melting moments
1 Look at this diagram of a candle. Fill in each box with the correct word: solid, liquid or gas.
2 Write each sentence in the correct box on the diagram below.
Water turns into ice.
Temperature inside a fridge.
Wax melts at about this temperature.
Temperature inside a freezer.
A hot summer day.
Water boils.
8Fe6 Does hot water freeze faster than cold?
Some people have suggested that when you put hot water into a freezer, it turns into ice more quickly than cold water. Other people have described this as unscientific rubbish, and that common sense tells us that cold water must freeze first.
Any question or theory that can reasonably be investigated by an experiment can be called 'scientific'. If we get an unexpected result it may be a fluke or a poor experiment, but if other scientists confirm the unusual result then we have to change our theories, or look for a new explanation.
1 Is the statement at the top of the page a scientific statement? Explain your answer.
2 Which do you think will form ice quicker - hot or cold water? Explain your answer.
3 Carry out a mini-survey among your friends or family. Find out what they predict is going to happen.
4 Imagine you were going to do an experiment to answer this question in your kitchen at home. You should describe:
- what you are planning to do
- how you will make it a fair test
- what observations or measurements you will make
- how many observations you will make.
5 You might be allowed to do the experiment in class or at home. If you do it at home, MAKE SURE YOU ASK YOUR PARENTS BEFORE YOU START THE EXPERIMENT. DO NOT OPEN THE FREEZER TOO OFTEN, OTHERWISE YOU MIGHT DEFROST THE FOOD!
6 Record your results in a suitable way.
7 What conclusions can you draw? Do they agree with your predictions? Do they agree with the results of other people in the class?
8 How confident are you of your conclusions? Explain why.
8Fe7 Boiling points of mixtures
The table below shows the boiling points of water, ethanol (alcohol) and mixtures of the two liquids.
Use the data in the table to answer the questions which follow.
% of ethanol
% of water
100
0
90
79
80
20
82
70
30
85
60
40
50
92
94
96
98
99
1 What is the boiling point of pure ethanol?
2 What is the boiling point of pure water?
3 What is the mean (average) of these two temperatures?
4 What is the boiling point of the mixture which contains half ethanol and half water?
5 Would you have expected the answers to question 3 and 4 to be the same? Explain why.
6 Plot a graph of boiling point (y-axis) against percentage of water in the mixture (x-axis).
7 Join the points with a single smooth line. Describe the shape of the line.
8 Use your graph to estimate the temperature at which a mixture containing 75% ethanol would boil.
Research task
9 In the old days, before there were accurate measuring instruments, customs officers who were trying to catch smugglers used to estimate the purity of alcohol using gunpowder. See if you can find out about 'proof spirit' and how the gunpowder test worked.
[ numeracy, considering, research ]
8Fe8 Melting mixtures of metals
Most metals have high melting points. Tin and lead are both metals that melt quite easily. The melting points of tin and lead are 232 °C and 328 °C. Solder is a mixture of tin and lead. It is used for joining metals together because it can be easily melted.
1 Plot a graph on graph paper to show the melting point of the mixtures of tin and lead against the percentage of tin in the mixture. Use axes like this.
Percentage of tin
Percentage of lead
Melting point (°C)
328
305
25
75
270
210
205
220
232
2 What can you say about the melting point of the mixture, compared with the melting point of a pure metal?
3 Use your graph to estimate:
a the lowest melting temperature that you could get from a mixture of tin and lead
b the percentage of tin and lead in this mixture.
4 Lead atoms are larger than atoms of tin. Draw particle diagrams that show the arrangement of atoms in:
a solid lead
b solid tin
c solid solder.
5 Use your particle diagrams to suggest reasons why the solder might melt more easily than either pure tin or pure lead.
[ knowledge, considering, numeracy ]
8F Summary Sheets
Compounds and mixtures
Elements are simple substances which cannot be split up in chemical reactions. Atoms are the smallest particles of an element that can exist. Atoms of an element are all the same.
Each element has its own chemical symbol. For example, the chemical symbol for oxygen is O.
Some elements have their atoms joined to each other in small groups called molecules. Oxygen is an example.
A molecule of oxygen consists of two oxygen atoms joined together.
Compounds
Elements can join together to make compounds. A compound contains two or more elements joined together. The name of the compound tells you the elements that are in it. Compounds made from two elements always have a name which ends in '-ide'.
Many compounds exist as atoms attached to each other in small groups - molecules.
A molecule of water.
The chemical formula tells you the numbers of atoms of each element in a compound. Each element in the chemical formula is shown by its chemical symbol. For example:
A compound always contains the same elements in the same ratio.
The properties of a compound are different from the elements that make it up. For example, hydrogen is an explosive gas and oxygen will relight a glowing splint but water is a liquid which will put fires out.
Chemical reactions
Compounds can react chemically by mixing them with other chemicals, or by using heat or electricity. You can tell that a chemical reaction has occurred if there is a colour change or when a gas is given off.
Most chemical reactions also involve an energy change. This is usually in the form of heat, but can also involve light being given off, for example, in burning (combustion).
In a chemical reaction a new substance is always formed. Most chemical reactions are not easily reversed (they are irreversible).
Some chemical reactions take place just by mixing. When you make a solid by mixing two liquids, the solid is called a precipitate.
Other chemical reactions need energy to start them off. This energy can be in the form of heat, light or electricity. When you use energy to split up compounds they are decomposed.
We can write word equations to show a chemical reaction. The chemicals that you start with are called the reactants. The chemicals at the end are called the products. For example:
magnesium + oxygen → magnesium oxide
reactants product
Physical changes
In a physical change no new substance is formed. Melting, evaporating, condensing and freezing are all examples of physical changes.
For example:
Mixtures
Elements and compounds can also be mixed together. A mixture is easier to separate than the elements in a compound. Soil, river water and sea water are examples of mixtures that occur naturally.
Elements and compounds melt and boil at a fixed temperature. Mixtures do not have definite melting points and boiling points.
Air is a mixture of gases - most of the air is nitrogen and oxygen. The gases in the air can be separated by fractional distillation.
8F Target Sheet
Topic
Targets
Before the unit
I have learned this
I have revised this
8Fa
Know what an atom is.
Know what a molecule is.
Know the difference between an element and a compound.
Know how to recognise the difference between an element and a compound using particle diagrams or formulae.
8Fb
Know what to look for to see if a reaction has occurred.
Know the meaning of the words reactant and product.
Describe some chemical reactions caused by heating.
Write word equations for chemical reactions.
8Fc
Know what a mixture is.
Know some examples of mixtures.
Know what pure water is.
Know why different types of bottled water taste different.
8Fd
Know that many drinks are mixtures.
Know the names of different gases in the air.
Know how the gases in the air can be separated.
Know some other ways of separating mixtures.
8Fe
Know how the melting point and the freezing point of a substance are linked.
Know the boiling point and freezing point of pure water.
Know the effect of impurities on the melting and boiling points of substances.
Know how to use melting and boiling point data to decide if a substance is pure.
8F Word Sheets
Word sheets that include new words from the 'Focus on:' pages are available on the Exploring Science website.
8Fa - Let's stick together/Coming together
Word
Pronunciation
Meaning
atom
The smallest part of an element.
bond
Force holding atoms together.
chemical formula
A combination of symbols and numbers that shows how many atoms of different kinds are in a particular molecule. In compounds that do not form molecules, it shows the ratio of elements in the compound.
compound
Substance that can be split up into simpler substances.
element
A substance that cannot be split up into anything simpler by chemical reactions.
molecule
Two or more atoms joined together.
oxide
A compound that includes oxygen.
8Fb - All change/Split ends
decompose
Break down into simpler parts.
irreversible change
Permanent change.
physical change
fizz-ick-al
A change where no new substances are formed.
precipitate
pres-sip-it-tate
Insoluble solid produced by mixing two solutions.
product
New chemical formed in a chemical reaction.
8Fc - All mixed up
mixture
Two or more different kinds of particles that are not chemically joined to each other.
pure
A substance that does not have anything else in it.
8Fd - Separating it out
chromatography
krow-mat-og-graph-ee
Separating dissolved solids from one another. The solids are usually coloured.
distillation
Separating a liquid from a solution by evaporating the liquid and then condensing it.
8Fe - Boiling in the freezer
boiling point
When a liquid is at its boiling point it is as hot as it can get. It is evaporating as fast as it can.
evaporate
When a liquid turns into a gas.
freezing point
The temperature at which a liquid turns into a solid.
melting point
The temperature at which a solid turns into a liquid.