Preparation of Salts (Cambridge (CIE) IGCSE Chemistry): Exam Questions

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

Complete the boxes to identify the pieces of apparatus labelled.

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

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.

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

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.

Which point appears to be inaccurate?

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]

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]

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

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

Complete the boxes to identify the pieces of apparatus labelled.

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]

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

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

Complete the empty boxes to name the pieces of apparatus.

What type of chemical reaction is the burning of magnesium?

Suggest a pH for the solution of magnesium hydroxide.

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

Why is the sulfuric acid warmed?

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

What method is used in Step 3? 

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

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

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

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

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

i) What is meant by the term saturated solution?

 [2]

 ii) What practical method could show the solution to be saturated?

 [1]

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

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.

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