Question

On electrolysis of dilute sulphuric acid using platinum electrodes, the product obtained at the anode will be

• A. Hydrogen
• B. Oxygen
• C. Hydrogen sulphide
• D. Sulphur oxide

Answer 1

The correct option is B

Oxygen

Electrolysis is defined as a process of decomposing ionic compounds into their elements by passing a direct electric current through its aqueous solution.

• On passing electricity sulfuric acid dissociate in an aqueous solution to produce hydrogen ion and sulfate ion

$\underset{\mathrm{Sulfuric}\mathrm{acid}}{{\mathrm{H}}_2{\mathrm{SO}}_4}\to \underset{\mathrm{Hydrogen}\mathrm{ion}}{2{\mathrm{H}}^{+}}+\underset{\mathrm{Sulfate}\mathrm{ion}}{{\mathrm{SO}}_4^{2-}}$

• water dissociates to give hydrogen ions and hydroxide ion

$\underset{\mathrm{Water}}{{\mathrm{H}}_2\mathrm{O}}\to \underset{\mathrm{Hydrogen}\mathrm{ion}}{{\mathrm{H}}^{+}}+\underset{\mathrm{Hydroxide}\mathrm{ion}}{{\mathrm{OH}}^{-}}$

At cathode: The cathode is a negative electrode and during electrolysis reduction reaction occurs at the cathode which results in the formation of hydrogen gas.$2{\mathrm{H}}_{\left(\mathrm{aq}\right)}^{+}+2{\mathrm{e}}^{-}\to {\mathrm{H}}_{2\left(\mathrm{g}\right)}$

The reduction of hydrogen takes place by gaining electrons.

At anode: Anode is a positive electrode and during electrolysis, an oxidation reaction occurs at the anode. The sulfate ions (${\mathrm{SO}}_4^{2-}$)and hydroxide ions (${\mathrm{OH}}^{-}$) are attracted to the positive electrode. But the sulfate ion is too stable and nothing happens. But hydroxide ions oxidized to result in the formation of Oxygen gas.

$4{\mathrm{OH}}_{\left(\mathrm{aq}\right)}^{-}\to 2{\mathrm{H}}_2{\mathrm{O}}_{\left(\mathrm{l}\right)}+{\mathrm{O}}_{2\left(\mathrm{g}\right)}+4{\mathrm{e}}^{-}$