Question

A high school chemistry student wishes to demonstrate how water can be separated into hydrogen and oxygen by electrolysis. She knows that the reaction will proceed more rapidly if an electrolyte is added to the water, and has 2.00 M solutions of these reagents available: H2SO4, HCl, NaCl, Na2SO4, Na2CO3, and CaCO3. which one would you use?

Answer 1

We use H2SO4 as an electrolyte to electrolyse water.

Because, it will not interfere with the electrode reacions of ions water.

H2SO4 will give H+ and SO4^2- ions. H^+ will not affect the cathode reaction as water also gives H2 gas at cathode.

SO4^2- also will not interfere with anode electrode because it is more stable and does not undergo oxidation.

Note:

* Addition of HCl will give H^+ and Cl^- ions where Cl^- ions are more active to undergo oxidation than water and hence Cl2 gas is produced instead of O2 gas.

* Addition of NaCl will give Na^+ and Cl^- ions where Cl^- ions are more active to undergo oxidation than water and hence Cl2 gas is produced at anode instead O2 gas.

* Similarly remaining salts will also cause some interference at electrodes.

So, to avoid interference of electrode reactions and only to increase the electrical conductivity of water we use H2SO4 as electrolyte.