O LevelChemistryCambridge (CIE)Exam Questions7. Acids, Bases & Salts7.3 Preparation of Salts

Preparation of Salts (Cambridge (CIE) O Level Chemistry): Exam Questions

Exam code: 5070

4 hours43 questions

Select a download format for 7.3 Preparation of Salts

Scroll for more

Select an answer set to view for
7.3 Preparation of Salts

1a
2 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.

A four-stage diagram. Stage 1: 50 cm3 of dilute nitric acid from a bottle is measured in a tall, narrow graduated container. Stage 2: the acid is in a beaker heated on a gauze. A thin straight rod stands in the beaker with a curved arrow showing it being moved round, and an empty box has a line pointing to the rod. A small spoon carries lead(II) oxide into the beaker from a shallow, wide, curved dish holding more of the solid, and a second empty box has a line pointing to the dish. Stage 3: the mixture was separated. Stage 4: a beaker of solution of lead(II) nitrate was allowed to cool.

Complete the boxes to identify the pieces of apparatus.

How did you do?

1b
1 mark

Why is the dilute nitric acid heated?

How did you do?

1c
2 marks

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

Two balance diagrams, each with a dish of solid on a balance and an enlarged scale beside it, with a pointer marking the reading. Before: the dish is heaped with solid and the scale runs from 16 to 19 g, with the pointer four small divisions above 17. After: only a little solid is left and the scale runs from 12 to 15 g, with the pointer three small divisions above 13. Each small division is 0.2 g.

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

How did you do?

1d
3 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]

How did you do?

2a
2 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.

How did you do?

2b
2 marks

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

How did you do?

3a
3 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

How did you do?

3b
1 mark

Which point appears to be inaccurate?

How did you do?

3c
3 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?

3d
2 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]

How did you do?

3e
3 marks

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

How did you do?

4a
3 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?

4b
2 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]

How did you do?

4c
2 marks

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

How did you do?

5a
3 marks

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

A three-stage diagram. Stage 1: a strip of burning magnesium is held by a pair of long hinged metal arms, with a shallow curved dish beside it. The label reads magnesium burning to form magnesium oxide. An empty box has a line pointing to the hinged arms and a second empty box has a line pointing to the curved dish. Stage 2: the magnesium oxide is tipped into water, which is heated. Stage 3: Universal Indicator solution is poured from a test tube into a straight-sided container of solution of magnesium hydroxide, and the indicator turns blue. A third empty box has a line pointing to this container.

Complete the empty boxes to name the pieces of apparatus.

How did you do?

5b
1 mark

What type of chemical reaction is the burning of magnesium?

How did you do?

5c
1 mark

Suggest a pH for the solution of magnesium hydroxide.

How did you do?

6a
1 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?

How did you do?

6b
1 mark

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

How did you do?

6c
1 mark

What method is used in Step 3? 

How did you do?

6d
1 mark

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

How did you do?

6e
2 marks

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

How did you do?

7a
1 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?

7b
1 mark

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

How did you do?

7c
3 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?

7d
1 mark

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

How did you do?

8a
3 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.

How did you do?

8b
3 marks

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

How did you do?