Home / iGCSE Chemistry (0620) Core:6.3 Reversible reactions and equilibrium: Exam Style Questions Paper 1

iGCSE Chemistry (0620) Core:6.3 Reversible reactions and equilibrium: Exam Style Questions Paper 1

iGCSE Chemistry (0620) Core Paper 1 - All Chapters
Question

When blue copper(II) sulfate is heated, a white solid and water are formed.

The white solid turns blue and gives out heat when water is added to it.

Which terms describe the blue copper(II) sulfate and the reactions?

 blue copper(II) sulfate isreactions
Aa mixturecan be reversed
Ba mixturecannot be reversed
Chydratedcan be reversed
Dhydratedcannot be reversed
▶️ Answer/Explanation
Solution

Ans: C

The blue copper(II) sulfate is hydrated copper sulfate (CuSO4·5H2O), which contains water molecules in its crystal structure. When heated, it loses water to form anhydrous white copper(II) sulfate (CuSO4).

The reaction is reversible because adding water to the white anhydrous copper(II) sulfate reforms the blue hydrated form. The heat given out when water is added indicates the reverse reaction is exothermic.

This makes option C correct: the original blue substance is hydrated, and the reactions can be reversed by adding or removing water.

Question

Which reaction can be easily reversed?

A dissolving zinc in hydrochloric acid

B fermenting glucose with yeast

C heating hydrated cobalt(II) chloride

D the rusting of an iron nail

▶️Answer/Explanation

Ans:C

When the hydrated cobalt(II) chloride is heated, it undergoes a process called dehydration, where the water molecules are removed, leaving behind the anhydrous cobalt(II) chloride. This reaction can be reversed by adding water back to the anhydrous cobalt(II) chloride, resulting in the reformation of the hydrated cobalt(II) chloride.

The dehydration and rehydration processes are reversible because they involve only physical changes and do not involve any chemical reactions. The addition or removal of water molecules does not alter the chemical composition of cobalt(II) chloride.

Question

 The diagram shows the change from an anhydrous salt to its hydrated form.

Which statement is correct?
A The forward reaction requires heat and water.
B The forward reaction requires water only.
C The reverse reaction requires heat and water.
D The reverse reaction requires water only.

▶️Answer/Explanation

Ans: B

The forward reaction requires water only as it is a hydration reaction. 

The reverse reaction requires heat only as it is a dehydration reaction.

Question

When blue-green crystals of nickel(II) sulfate are heated, water is produced and a yellow solid remains. When water is added to the yellow solid, the blue-green colour returns. Which process describes these changes?

A. combustion
B. corrosion
C. neutralisation
D. reversible reaction

▶️Answer/Explanation

Ans:

D

The dehydration and rehydration processes are reversible because they involve only physical changes and do not involve any chemical reactions. The addition or removal of water molecules does not alter the chemical composition of nickel(II) sulfate. 

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