ย 

Electrolysis for SQA National 5 Chemistry

Electrolysis

This page covers the following topics:

1. Electrolysis setup
2. Electrolysis of molten compounds

Electrolysis is the passing of a current through an electrolyte, which moves ions towards respective electrodes, and two separate reactions happen at each of them. The anode, the positive electrode, attracts and oxidises negative ions. The cathode, the negative electrode, attracts and reduces positive ions.

During many of the electrolysis reactions, pure elements are produced. For example:
2AlBrโ‚ƒ โ†’ 2Al + 3Brโ‚‚
The overall reaction can be split to represent processes happening at specific electrodes by using half-equations, such as:
Alยณโบ + 3eโป โ†’ Al
2Brโป โ†’ Brโ‚‚ + 2eโป

Electrolysis setup

Some compounds during their electrolysis produce metals that are highly reactive. If these metals are exposed to water, they react with it and it is therefore not possible to obtain pure metals. Electrolysis of molten compounds can be used to address this issue and separate substances that produce reactive metals.

Platinum or graphite electrodes are commonly used for electrolysis due to being relatively unreactive. Graphite is a less expensive option; however, over the time it can react with oxygen to produce carbon dioxide.

Electrolysis of molten compounds

1

Provide a balanced chemical reaction for the electrolysis of a molten compound shown in the image.

During many of the electrolysis reactions, pure elements are produced. Since sodium chloride contains sodium and chloride elements, sodium metal and chloride gas are produced during this reaction.

2NaCl โ†’ 2Na + Clโ‚‚

Provide a balanced chemical reaction for the electrolysis of a molten compound shown in the image.

2

Provide a chemical equation for the electrolysis of copper(II) chloride.

During many of the electrolysis reactions, pure elements are produced. Since copper chloride contains copper and chlorine elements, copper metal and chlorine gas are produced during this reaction.

CuClโ‚‚ โ†’ Cu + Clโ‚‚

Provide a chemical equation for the electrolysis of copper(II) chloride.

3

What two materials are commonly used for electrodes during the electrolysis of molten compounds?

Platinum or graphite electrodes are commonly used for electrolysis due to being relatively unreactive.

platinum, graphite

What two materials are commonly used for electrodes during the electrolysis of molten compounds?

4

Name component X within the electrolysis setup displayed in the image provided.

The negative electrode in an electrolysis setup is called cathode.

cathode

Name component X within the electrolysis setup displayed in the image provided.

5

Name one advantage and one disadvantage of using graphite electrodes for the electrolysis of molten compounds in comparison to using platinum electrodes.

Platinum or graphite electrodes are commonly used for electrolysis due to being relatively unreactive. Graphite is a less expensive option; however, over the time it can react with oxygen to produce carbon dioxide.

Graphite is less expensive but it slowly reacts with oxygen.

Name one advantage and one disadvantage of using graphite electrodes for the electrolysis of molten compounds in comparison to using platinum electrodes.

End of page

ย