Electrolysis Examples

Chemistry: Cambridge International GCSE Supplement, topic 4.1.2

You need to be able to describe the electrode products and the observations made during the electrolysis of:

When we use graphite electrodes to apply electricity across molten lead bromide, we form lead (metal) at the cathode and bromine (non-metal) at the anode.
Lead bromide → lead + bromine
We know lead is present if a shiny metal forms around the cathode.
Bromine is observed as a brown gas because of the high temperatures reached in the process.

Applying electricity across hydrochloric acid with graphite electrodes produces hydrogen gas at the cathode and chlorine gas (non-metal) at the anode.
We can detect hydrogen at the cathode using a lit splint. A squeaky pop is heard.
We can detect chlorine gas by its smell. It also bleaches litmus paper.

The electrolysis of aqueous solutions is a little more complex, as you have to consider the water.
In the case of aqueous sodium chloride, hydrogen is formed instead of sodium.
Applying electricity across aqueous sodium chloride produces hydrogen gas at the cathode and chlorine gas (non-metal) at the anode.
The electrodes are inert graphite or platinum.
The formation of hydrogen at the cathode can be detected using a lit split. A squeaky pop is heard.
The chlorine gas can be detected by its smell. It also bleaches litmus paper.

When dilute sulfuric acid is electrolysed, hydrogen is produced from the acid and oxygen from the water.
Applying electricity to sulfuric acid with graphite electrodes produces hydrogen gas at the cathode and oxygen at the anode.
The formation of hydrogen at the cathode can be detected using a lit split. A squeaky pop is heard.
The oxygen gas produced at the anode can also be detected using a glowing splint. The splint will relight in oxygen gas.

Test yourself on Electrolysis Examples

During the electrolysis of concentrated aqueous sodium chloride, what is formed at the anode and cathode?