Electrolysis (Cambridge (CIE) O Level Chemistry): Exam Questions

Electricity was used to break down dilute sulfuric acid using the apparatus shown.

What name is given to this process?

Give one observation which could be made during this experiment.

Suggest a suitable metal for the inert metal electrodes.

Give a test for oxygen gas.

test .............................................................................................. result ...........................................................................................

Why does hydrogen form at the negative electrode?

The experiment was repeated using concentrated hydrochloric acid. Explain why this experiment was carried out in a fume cupboard.

Electricity was passed through a solution of concentrated hydrochloric acid using the apparatus shown.

Complete the boxes to identify the parts of the apparatus labelled.

Describe the test for hydrogen.

test ......................................................................................................... result  ....................................................................................................

Describe how a sample of the gas given off at the positive electrode could be collected and its volume measured.

The experiment was repeated using a concentrated aqueous solution of sodium chloride instead of hydrochloric acid.

i)

State the name of the solution formed.

[1]

ii)

Give a test to show the presence of this product.

[1]

Electricity was passed through aqueous copper(II) sulfate using inert electrodes as shown in the diagram below. Copper was deposited at one of the electrodes.

Name a suitable material for the electrodes.

At which electrode was copper deposited?

Give one other observation seen during the electrolysis.

The electrode at which copper was deposited was removed at intervals, washed, dried and weighed. The results are shown below.

i)

Suggest how the electrode was washed?

[1]

ii)

How could the electrode be dried quickly?

[1]

Complete the table from part d) by calculating the total increase in mass for the remaining time intervals.

Plot the points on the grid below. Draw a graph with two intersecting straight lines.

Suggest why the last three readings were the same.

A concentrated solution of sodium chloride was electrolysed using the apparatus below.

One observation noted was that the Universal Indicator turned purple at the negative electrode.

What observation would be made at both electrodes?

Why did the indicator turn purple at the negative electrode?

i)

Name the product formed at the positive electrode.

 [1]

ii)

Suggest the effect of this product on the Universal Indicator.

 [1]

The diagram shows an experiment to pass electricity through lead bromide.

Electricity has no effect on solid lead bromide

i)

Clearly label the electrodes on the diagram.

[1]  

ii)

Suggest a suitable material to make the electrodes.

[1]

Give two observations expected when the lead bromide is heated to melting point.

State two different safety precautions when carrying out this experiment.

Electricity was passed through a concentrated solution of sodium chloride containing Universal Indicator. 

Suggest a suitable material for the electrodes. 

Three observations were noted:

1. Bubbles of gas seen immediately at the negative electrode.

2. Bubbles of gas formed after some time at the positive electrode.

3. The solution turned blue around the negative electrode and colourless near the positive electrode.

Give a test to show that the gas observed in 1 is hydrogen.

test ........................................................................................ result .....................................................................................

Suggest why bubbles of gas were not seen immediately in 2.

What causes the colour change in 3 at: the negative electrode ........................................................................................... the positive electrode? ...........................................................................................

The diagram shows the apparatus used to find out the effect of an electric current on a concentrated aqueous solution of sodium chloride. 

On the diagram label the electrodes.

Give three observations when the circuit is switched on.

i)

Name the product at the positive electrode (anode).

[1]

ii)

State a test for this product and the result of the test.

[2]

Lead bromide was placed in a tube and connected to an electrical circuit as shown below.  

The lead bromide was heated until molten. A brown gas was given off.

State one other expected observation.

i)

Suggest a suitable material for the electrodes.

[1]

ii)

Indicate on the diagram the negative electrode (cathode).

[1]

Name the brown gas. At what electrode will the gas be given off? name ........................................................................ electrode ..................................................................

Why is this experiment carried out in a fume cupboard?

The diagram shows the effect of passing electricity through concentrated hydrochloric acid. 

Label the diagram by completing the boxes. 

Name this process.

Give a test for chlorine.