Electrolysis (OCR Gateway GCSE Chemistry)

Electrolysis can be used to separate the elements in some compounds using electricity.

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Molten lead bromide contains lead ions, Pb²⁺, and bromide ions, Br⁻.

What is the formula for lead bromide?

Tick () one box.

PbBr
PbBr2
Pb2Br
Pb2Br2

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The student investigates the mass of copper made during the electrolysis of aqueous copper chloride.

The student varies the electric current and passes the current for the same time in each experiment. Here is a table of their results.

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Current = ....................................................... A

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Mass of copper produced = ....................................................... g

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A student electrolyses dilute sulfuric acid.

Hydrogen gas is made at the cathode.

The student measures the volume of hydrogen made at the cathode every 2 minutes for 10 minutes.

Look at his results.

Plot the results on the grid. The first 3 points have been done for you.

Draw a line of best fit.

One of the results is anomalous.

Circle the anomalous result on the graph.

Sulfuric acid contains these particles.

Which particles are attracted to the anode?

A student electrolyses copper sulfate using copper electrodes.

Look at the diagram. It shows the apparatus she uses.

She investigates the change in mass at each electrode before and after the electrolysis.

Look at her method.

What improvements could you make to the student’s experiment?

Explain your answers.

The student finds that:

• the cathode gains mass
• the anode loses mass.

Explain these observations in terms of the reactions at each electrode.

A student investigates the electrolysis of aqueous solutions of ionic compounds

Write the formulae of the ions that are present in aqueous copper sulfate solution.

Why is it important that the investigation is done with inert electrodes?

Electroplating is used to cover a metal with another metal.

Tick () one box.

Copper sulfate
Zinc bromide
Copper chloride
Sulfuric acid

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The electrolysis products of ionic compounds can be different in the molten or aqueous states.

Suggest why.

A student is investigating the electrolysis of copper sulfate solution.

He does two experiments.

Experiment 1 uses platinum electrodes. Experiment 2 uses copper electrodes.

Complete the table to show the products at each electrode.

Copper electrodes are non-inert electrodes.

What is meant by non-inert electrodes?

HIgher Only

Look at the results for experiment 2 using copper electrodes.

At the cathode copper ions, Cu²⁺ gain electrons to make copper atoms.

Write the half equation for this reaction.

Use e^–  to represent an electron.

The student also electrolyses sodium chloride solution using platinum (inert) electrodes.

At the cathode, hydrogen gas is made rather than sodium metal.

Explain why.