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IGCSEChemistry: Co-ordinated Sciences (Double Award)CIEExam QuestionsAcids, Bases & SaltsPreparation of Salts

Preparation of Salts (CIE IGCSE Chemistry: Co-ordinated Sciences (Double Award))

Exam Questions

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Preparation of Salts

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Preparation of Salts

1a2 marks

A student reacted dilute nitric acid with lead(II) oxide to prepare lead(II) nitrate. The diagram shows the stages in the method used.

7-2-q1a

Complete the boxes to identify the pieces of apparatus.

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1b1 mark

Why is the dilute nitric acid heated?

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1c
Sme Calculator2 marks

The lead(II) oxide was weighed before and after the additions.

7-2-q1c

Use the balance diagrams to work out the mass of lead(II) oxide added to the dilute nitric acid.

How did you do?

1d3 marks
i)
How would the student know when all of the dilute nitric acid had reacted in stage 2?

[1]

ii)
What method is used to separate the mixture in stage 3?

[1]

iii)
What term is used to describe the unreacted lead(II) oxide?

[1]

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2a2 marks

A student reacted excess iron powder with sulfuric acid to prepare a solution of iron(II) sulfate.
 The diagram shows the procedure followed in three stages

7-2-q2a

Complete the boxes to identify the pieces of apparatus labelled.

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2b2 marks

How would the student know when all of the sulfuric acid had reacted? Give two reasons.

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3a3 marks

A student prepared a sample of potassium nitrate by neutralising nitric acid using potassium hydroxide solution.

25.0 cm3 of nitric acid was poured into a conical flask. Potassium hydroxide was added a little at a time from a burette as shown below.

7-2-q3a-equip

After each addition of potassium hydroxide solution the pH was measured with a pH meter and the values recorded in the table of results.

volume of potassium hydroxide
solution added / cm3		 pH value
5.0 1.2
10.0 1.4
15.0 2.6
20.0 2.0
24.0 2.7
24.5 3.0
25.5 11.0
26.0 11.3
30.0 12.0
40.0 13.2

You are going to draw a graph to find the volume of potassium hydroxide solution required to neutralise the 25.0 cm3 of nitric acid.

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

7-2-q3a-graph

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3b1 mark

Which point appears to be inaccurate?

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3c3 marks
i)
Use your graph to find the pH of the solution when 35.0 cm3 of potassium hydroxide was added.

[1]

ii)
Use your graph to find the pH of 25.0 cm3 of nitric acid.

Show clearly on the grid how you obtained your answer.

[2]

How did you do?

3d2 marks
i)
What is the pH of the solution when all of the nitric acid has just been neutralised?

[1]

ii)
What volume of potassium hydroxide was required to neutralise 25.0 cm3 of nitric acid?

[1]

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3e3 marks

Describe how the student should modify the experiment to obtain pure crystals of potassium nitrate.

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4a3 marks

A student reacted nitric acid with magnesium oxide to prepare magnesium nitrate. The diagram shows the procedure followed in three stages.

making-magnesium-nitrate

Complete the boxes to identify the pieces of apparatus labelled.

How did you do?

4b2 marks
i)
What term is used to describe the unreacted magnesium oxide?
 
[1]
 
ii)
What method is used to remove the unreacted magnesium oxide after stage 3?
 
[1]

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4c2 marks

Describe how crystals of magnesium nitrate could be quickly obtained from the solution.

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5a3 marks

The diagram shows the formation of a solution of magnesium hydroxide from magnesium.

making-magnesium-hhydroxide

Complete the empty boxes to name the pieces of apparatus.

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5b1 mark

What type of chemical reaction is the burning of magnesium?

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5c1 mark

Suggest a pH for the solution of magnesium hydroxide.

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6a1 mark

The following instructions were used to prepare magnesium sulfate crystals, MgSO4.7H2O.

Step 1  Measure 50 cm3 of dilute sulfuric acid into a beaker and warm the solution.
Step 2 Using a spatula, add some magnesium oxide and stir the mixture. Continue adding the magnesium oxide until excess is present.
Step 3  Separate the excess magnesium oxide from the solution of magnesium sulfate.
Step 4  Heat the solution until crystals form. Obtain the crystals and dry them.

Why is the sulfuric acid warmed?

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6b1 mark

How would you know when excess magnesium oxide is present in Step 2? 

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6c1 mark

What method is used in Step 3? 

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6d1 mark

Why must care be taken when drying the crystals in Step 4?

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6e2 marks

Explain how the method would differ if magnesium carbonate was used instead of magnesium oxide.

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7a1 mark

The information in the box is about the preparation of zinc nitrate crystals.

Step 1: Add a small amount of zinc oxide to some hot dilute nitric acid, and stir.

Step 2: Keep adding zinc oxide until it is in excess.

Step 3: Remove the excess zinc oxide to leave colourless zinc nitrate solution.

Step 4: Evaporate the zinc nitrate solution until it is saturated.

Step 5: Leave the saturated solution to cool. White crystals form on cooling.

Step 6: Remove the crystals from the remaining solution.

Step 7: Dry the crystals on a piece of filter paper.

Suggest a reason for using excess zinc oxide in Step 2.

How did you do?

7b1 mark

Suggest how the excess zinc oxide can be removed from the solution in Step 3.

How did you do?

7c3 marks
i)
What is meant by the term saturated solution?
 
[2]
 
ii)
What practical method could show the solution to be saturated?
 
[1]

How did you do?

7d1 mark

Why are the crystals dried in Step 7 using filter paper instead of by heating?

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8a3 marks

A solution of magnesium sulfate can be made by reacting magnesium oxide with warm sulfuric acid. 

Describe how you could make a solution of magnesium sulfate starting with magnesium oxide powder and dilute sulfuric acid.

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8b3 marks

Describe how you would obtain pure dry crystals of hydrated magnesium sulfate, MgSO4.7H2O, from the solution of magnesium sulfate in (a). 

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