experiment gf24d29202 1280 Electrolysis Of Dilute Sulphuric Acid (Electrolysis Of Water)

Electrolysis Of Dilute Sulphuric Acid (Electrolysis Of Water)


Dilute sulphuric acid is a mixture of sulphuric acid and water. It is a very strong acid and a good electrolyte. The products of the electrolysis of dilute sulphuric acid totally depends on the order of preferential discharge of ions.

Dilute sulphuric acid dissociates as follows:

H2SO4(aq) โ†’ 2H+(aq) + SO42-(aq)

H2O(l) โ‡Œ H+(aq) + OHโ€“(aq)

This means that dilute sulphuric acid contains the following ions, H+, SO42- and OHโ€“.

At the anode

SO42- and OHโ€“ ions move to the anode, but due to the order of preferential discharge OHโ€“ are discharged before SO42-. They lose electrons to form water and oxygen gas.

The anode reaction is as follows:

4OHโ€“(aq) โ€“ 4e โ†’ 2H2O(l) + O2(g)

At the cathode

H+ are the only positively charged ions in the solution. They move to the cathode where they gain electrons to form hydrogen gas.

The cathode reaction is as follows:

2H+(aq) + 2e โ†’ H2(g)


Overall result

As the water ionises around the cathode to produce OHโ€“ ions which are then discharged, the accompanying H+ ions increases the acidity of the electrolyte around the anode. At the cathode, H+ ions are discharged, decreasing the acidity of the electrolyte around the cathode.

The number of electrons gained by the H+ at the cathode should be equal to the number of electrons deposited by 4OHโ€“(aq) at the anode according to the law of conservation of charge. Balancing the charge on the cathode and anode reactions, we get:

4OHโ€“(aq) โ€“ 4e โ†’ 2H2O(l) + O2(g)

and

4H+(aq) + 4e โ†’ 2H2(g)

From the balanced ionic equations we can see the hydrogen gas produced is twice as much as the oxygen gas.

Why the electrolysis of dilute sulphuric acid is also known as the electrolysis of water

The products of the electrolysis of dilute sulphuric acid are the components of water. The hydrogen and oxygen are produced in the ratio 2:1 respectively, which corresponds to the chemical formula of water (H2O). This proves that the water in dilute sulphuric acid is the only component being broken up.