Separation & Purification (Cambridge (CIE) IGCSE Chemistry)

Exam Questions

6 hours61 questions
1a5 marks

A student investigated the solubility of salt A in water at various temperatures. Five experiments were carried out. Experiment 1 The student was provided with a boiling tube containing 12 g of salt A.

A burette was filled with distilled water and 10.0 cm3 of water was added to the boiling tube.

The mixture of salt A and water was heated until all of the solid had dissolved.

The boiling tube was removed from the heat and the solution was stirred with a thermometer and allowed to cool.

The temperature at which crystals first appeared was measured. 

Use the thermometer diagram to record the temperature in the table of results.

screen-shot-2022-09-28-at-10-11-24

The boiling tube and contents were kept for the next four experiments.

Experiment 2

From the burette, 1.0 cm3 more of water was added into the boiling tube and contents from Experiment 1.

The experiment was repeated exactly as before to find the temperature at which crystals first appeared.

The boiling tube was dipped for short periods of time in a beaker of cold water to speed up the cooling.

Record, in the table of results, the total volume of water in the boiling tube.

Use the thermometer diagram to record the temperature at which crystals first appeared.

screen-shot-2022-09-28-at-10-11-34

Experiment 3

From the burette 1.0 cm3 more of water was added into the boiling tube and contents from Experiment 2.

The experiment was repeated exactly as before.

Record, in the table of results, the total volume of water used.

Use the thermometer diagram to record the temperature at which crystals first appeared.

screen-shot-2022-09-28-at-10-15-37

This procedure was continued for Experiments 4 and 5 with two more successive additions of 1.0 cm3 of water. Note all the results in the table.

screen-shot-2022-09-28-at-10-15-42

Table 1 (Table of results)

Experiment 

total volume of water cm3

temperature at which crystals first appeared / °C

1

10

2

3

4

5

1b6 marks

Plot the results on the grid below and draw a straight line graph.

Graph 1 - crytalisation
1c1 mark

How did the student know when salt A was completely dissolved in the water? 

1d2 marks

From your graph, find the temperature at which crystals of salt A would first appear if the total volume of water in the solution was 9.0 cm3.

Show clearly on the grid how you worked out your answer. 

1e2 marks

Suggest, with a reason, how the results would be different if 6 g of salt A were used instead of 12 g of salt A.

1f2 marks

Salt B is more soluble in water than salt A.

Sketch on the grid the graph you would expect for salt B. Label this graph.

1g2 marks

Explain one improvement you could make to the experimental procedure to obtain more accurate results in this investigation.

improvement ..........................................................................................................

explanation ..........................................................................................................

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2a2 marks

The diagram shows the apparatus used to separate a mixture of water, boiling point 100 °C, and ethanol, boiling point 78 °C.

fractional-distillation---add-the-labels

Complete the boxes to name the apparatus.

2b1 mark

Label the arrows on the condenser.

2c1 mark

Identify one mistake in the apparatus.

2d2 marks

Which liquid would collect first? Explain your answer.

2e1 mark

Why would it be better to use an electrical heater instead of a Bunsen burner to heat the water and ethanol mixture?

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3a4 marks

An experiment was carried out to determine the solubility of potassium chlorate at different temperatures. The solubility is the mass of potassium chlorate that dissolves in 100 g of water. The results obtained are shown in the table below.

temperature/ °C

0

10

20

30

40

50

60

solubility in g/ 100g water

14

17

20

24

29

34

40

On the grid, draw a smooth line graph to show the solubility of potassium chlorate at different temperatures.

screen-shot-2022-09-28-at-14-55-58
3b2 marks

Use your graph to determine the solubility of potassium chlorate at 70 °C. Show clearly on the graph how you obtained your answer.

3c2 marks

What would be the effect of cooling a saturated solution of potassium chlorate from 60 °C to 20 °C?

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46 marks

Seawater contains sodium chloride and other salts.

Plan an experiment to find the mass of salts in 1 dm3 of seawater.

You will be provided with a small bottle of seawater.

You should include details of the method and any apparatus used.

(1 dm3 = 1000 cm3)

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56 marks

The label on a bottle of orange drink stated ‘contains no artificial colours’. A scientist thought that the orange colour in the drink was a mixture of two artificial colours:

  • Sunset Yellow E110

  • Allura Red E129

Plan an investigation to show that the orange colour in the drink did not contain these two artificial colours. You are provided with samples of E110, E129 and the orange colouring from the drink. You are also provided with common laboratory apparatus. You may draw a diagram to help answer the question.

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6a3 marks

The apparatus below was used to separate ethanol from water.

fractional-distillation---add-labels

Complete the empty boxes to name the pieces of apparatus.

6b1 mark

Indicate by an arrow where heat is applied.

6c2 marks

Name this separation process.

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76 marks

Copper(II) oxide and carbon are both black solids. Copper(II) oxide reacts with dilute sulfuric acid to form aqueous copper(II) sulfate. Carbon does not react with dilute sulfuric acid.

You are given a mixture of copper(II) oxide and carbon and access to dilute sulfuric acid.

Plan an experiment to investigate the percentage of copper(II) oxide in the mixture.

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8a2 marks

A student investigated the colours present in a fruit drink. The fruit drink was tested to check that no artificial colours had been added. The apparatus below was used.

cie-chromatography

i) Name the method used.

[1]

ii) Why is there a glass cover on the beaker?

[1]

8b1 mark

When should the paper be removed from the beaker?

8c3 marks

The diagram shows the results of the experiment.

cie-chromatogram

i) How many different coloured compounds were present in the fruit drink?

[1]

ii) Are there any of the artificial colours present in the fruit drink? Explain your answer.

[2]

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9a2 marks

The diagrams show the apparatus used to obtain crystals of calcium chloride from a mixture of solid calcium chloride and solid calcium carbonate. Calcium chloride is soluble in water and calcium carbonate is insoluble in water.

making-calcium-chloride-crystals

 Complete the boxes to name the apparatus. 

9b2 marks

i) Write down the order in which the apparatus should be used in this experiment.

 [1]

ii) Name the separation process in C.

[1]

9c2 marks

i) What has been added to the mixture in B?

 [1]

ii) What is the general name given to the liquid in the dish in C?

[1]

9d1 mark

How would you know when to stop heating the dish in A?

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107 marks

Toothbright toothpaste contains three compounds, sodium fluoride, calcium carbonate and water. Calcium carbonate is insoluble in water and sodium fluoride is soluble in water.

Plan an investigation to find out the percentage of calcium carbonate present in this toothpaste. You are provided with common laboratory apparatus.

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11a1 mark

A mixture of coloured dyes, M, was separated by chromatography. The dyes were insoluble in water.

The chromatogram below shows the result of separating the mixture and the chromatography of three known dyes 1, 2 and 3.

12-2q11a

On the diagram, label the base line (origin).

11b1 mark

Name a solvent that could be used in this separation.

11c1 mark

How many dyes were there in the mixture, M?

11d3 marks

What are your conclusions about the identity of the dyes in the mixture, M?

11e1 mark

How could the reliability of the results be checked?

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127 marks

Calcium carbonate is found in limestone and in marble. All carbonates react with hydrochloric acid to form chlorides. Calcium carbonate is insoluble in water but calcium chloride is water soluble. Most impurities in limestone and marble are insoluble.

Plan experiment to find out which of limestone and marble contain most insoluble impurities. You are provided with common laboratory apparatus.

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13a2 marks

A student separated a mixture of two alcohols, ethanol (boiling point 78 °C) and butanol (boiling point 118 °C).

The apparatus used is shown below. 

12-2q13a

Complete the boxes to identify the pieces of apparatus labelled.

13b1 mark

Label the arrows.

13c2 marks

State the name of this separation process. 

13d2 marks

i) Which liquid is first to collect in the beaker?

[1]

ii) How would the student know when all of this liquid had collected?

[1]

13e2 marks

Identify and explain a possible hazard in this experiment.

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14a1 mark

The following paragraph was taken from a student’s notebook:

12-2q14a

What type of chemical reaction resulted in the formation of the lead chloride?

14b2 marks

What is the solubility of lead chloride in:

i) Cold water?

[1]

ii) Hot water? 

[1]

14c1 mark

What method should be used to separate the crystals from the mixture?

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15a1 mark

The colours present in some fruit sweets can be separated using the apparatus below. The colours are water-soluble dyes. 

12-2q15a

Name the process used to separate the colours.

15b1 mark

Name the solvent used.

15c1 mark

The results obtained for the colours in two different sweets, C and D, are shown below.

12-2q15b

What is the name for the line at position B?

15d1 mark

What conclusions can you draw about the colours present in sweets C and D?

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16a1 mark

The diagram shows the results of an experiment to separate and identify the colours present in two coloured mixtures, A and B.

Substances C, D, E and F are single colours.

12-2q16

Name this method of separation.

16b1 mark

Draw a line on the diagram to show the level of the solvent at the beginning of the experiment.

16c1 mark

Why should a pencil be used instead of a pen to draw the origin line?

16d2 marks

State one difference and one similarity between the coloured mixtures, A and B.

difference ....................................................................................................

similarity ....................................................................................................

16e1 mark

Which substances are present in mixture A?

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17a3 marks

A solution of copper sulphate was made by reacting excess copper oxide with dilute sulphuric acid. The diagram shows the method used. 

12-2q17

Complete the empty boxes to name the pieces of apparatus.

17b1 mark

What does the term excess mean?

17c2 marks

Draw a labelled diagram to show how the mixture was filtered.

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18a3 marks

The colours present in some blackcurrant sweets can be separated by chromatography.

The colours are water-soluble dyes.

The diagrams show how the colours can be extracted from the sweets. 

rOa0I0SV_12-2q18

 

Complete the empty boxes to name the pieces of apparatus.

18b2 marks

The apparatus below was used to carry out the chromatography.

 

12-2q18b

 i) Name the solvent used.

 [1]

ii) Label, with an arrow, the origin on the diagram.

 [1]

18c1 mark

Sketch, in the box, the chromatogram you would expect if two different colours were present in the sweets.

12-2q18c

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19a3 marks

A mixture of ethanol and water can be separated by fractional distillation. The apparatus below can be used to carry out such a separation in the laboratory.  

12-2q19

Name each piece of apparatus.

A ....................................................................................................

B ....................................................................................................

C ....................................................................................................

19b1 mark

What is the purpose of D?

19c1 mark

How could the purity of the ethanol collected be checked?

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20a1 mark

Chromatography can be used to identify amino acids from a sample of protein.

The diagram shows the chromatogram obtained when four samples of amino acids were analysed. The paper was sprayed with ninhydrin. 

12-2q20

 Why is the origin line drawn in pencil?

20b1 mark

Which amino acids could possibly be the same?

20c2 marks

Which amino acid sample contains more than one amino acid? Explain your answer.

sample ....................................................................................................

explanation ....................................................................................................

20d1 mark

Suggest why it is necessary to spray the chromatogram with ninhydrin.

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21a2 marks

The green pigment chlorophyll can be obtained from grass.

 

Step 1: The grass is crushed with sand.

Step 2: The grass is ground with ethanol until the solution is saturated.

Step 3: The solution is separated from the rest of the mixture.

Step 4: The colours in the solution are separated.

What apparatus is used in Step 1?

21b1 mark

Suggest why the grass is ground with ethanol rather than water in Step 2.

21c1 mark

Name the separation method in Step 3.

21d
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4 marks

Describe how Step 4 is carried out.

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22a2 marks

Coffee beans contain caffeine and other compounds. Caffeine is soluble in water and in trichloromethane, an organic solvent. A student obtained crystals of caffeine by the following method.

Stage 1

Some coffee beans were crushed into small pieces.

Stage 2

Hot water was added to the crushed beans to dissolve the soluble substances.

Stage 3

The crushed beans were separated from the liquid solution.

Stage 4

The liquid was allowed to cool and shaken with trichloromethane to extract the caffeine from the water.

Stage 5

The caffeine was crystallised from the trichloromethane solution.

Stage 6

The caffeine crystals were checked for purity.

What apparatus should be used to crush the beans in Stage 1?

22b1 mark

How could the dissolving process in Stage 2 be speeded up? 

22c2 marks

Draw a diagram of the apparatus used in Stage 3. 

22d2 marks

How should Stage 5 be carried out?

22e1 mark

What method could be used to check the purity of the crystals in Stage 6?

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23a2 marks

A student extracted and investigated the orange colour in some sweets.

The student followed these instructions:

  1. Collect sweets, a watch glass, a beaker, eye protection and 100 cm3 of ethanol.

  2. Crush the sweets.

  3. Place the crushed sweets in the beaker containing 100 cm3 of ethanol.

  4. Boil the mixture with the watch glass covering the beaker.

  5. Decant the liquid and concentrate it by evaporation until the colour is dark orange.

  6. Investigate which colours are present in the orange solution.

Why should the sweets be crushed?

23b1 mark

Why should the experiment be carried out in a well-ventilated laboratory?

23c1 mark

State one safety precaution that the student should have taken, other than carrying out the experiment in a well-ventilated laboratory and using eye protection.

23d1 mark

State the purpose of the watch glass.

23e1 mark

Explain the term decant.

23f5 marks

Describe how the student could carry out instruction 6. You may draw a diagram in the space below to help you answer the question.

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246 marks

A fake banknote can be investigated by dissolving the ink off the paper. You are provided with four different inks from four different criminals.

Describe an experiment to show which one of these inks is the same as the ink from the banknote. You can use a labelled diagram to help you answer the question.

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25a3 marks

A student reacted sulphuric acid with copper(II) oxide. The diagram shows the procedure followed.

making-cuso4

Complete the boxes to identify the pieces of apparatus labelled.

25b1 mark

What is the colour of the solution formed?

25c2 marks

Describe how crystals could be quickly obtained from the solution.

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26a2 marks

E numbers identify chemicals which are added to foods.

E210 is benzoic acid. How could you show that a solution of benzoic acid is a weak acid?

test ..........................................................................................................

result ..........................................................................................................

26b1 mark

E211 is sodium benzoate. Name a suitable substance that would react with a solution of benzoic acid to form sodium benzoate.

26c4 marks

E110 is Sunset yellow. Outline a method you could use to show the presence of E110 in a food colouring. A space has been left if you want to draw a diagram to help you answer the question.

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27a1 mark

 The label below is from a bottle of concentrated lemon drink. 

Concentrated lemon drink

Ingredients: Water, sugar, citric acid, preservatives, potassium sorbate (artificial sweetener). Yellow colourings E102 and E104.

What is meant by the term concentrated?

27b1 mark

Predict the pH of the lemon drink.

27c4 marks

Describe an experiment to show that two different yellow colourings are present in the drink.

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28a3 marks

Leaves from trees contain a mixture of coloured pigments which are not soluble in water. A student was given these two instructions to investigate the pigments in the leaves.

  1. Crush some leaves to extract the coloured pigments.

  2. Use the liquid extract to find the number of coloured pigments in the leaves.

What would the student need in order to effectively carry out instruction 1?

28b4 marks

Describe an experiment to carry out instruction 2. A space has been left below if you want to draw a diagram to help answer the question.

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29a2 marks

This label is from a container of ‘Bite Relief’ solution.

12-2-q29a

Give a chemical test to show the presence of ammonia in Bite Relief solution.

test ..........................................................................................................

result ..........................................................................................................

29b2 marks

What practical method could be used to separate the mixture of alcohol (bp 78 °C) and water (bp 100 °C)?

29c2 marks

Give a chemical test to show the presence of water.

test ...............................................................................................

result ...........................................................................................

29d1 mark

What would be the effect of touching the alcohol with a lighted splint?

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30a1 mark

A sample of orange fruit jam was investigated to check the three colourings present.

Step 1: The jam was boiled with water.

Step 2: The mixture was filtered.

Step 3: The filtrate was concentrated.

Step 4: The concentrate was analysed by chromatography.

What was the purpose of Step 1?

30b1 mark

Why was the mixture filtered?

30c1 mark

How was Step 3 carried out?

30d2 marks

Draw a diagram to show the possible paper chromatogram obtained in Step 4.

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