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O LevelChemistryCambridgeExam Questions7. Acids, Bases & Salts7.3 Preparation of Salts

Preparation of Salts (Cambridge O Level Chemistry)

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7.3 Preparation of Salts

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7.3 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.

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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.

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7b1 mark

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

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

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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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