Ncert Exercises & Solutions

9.5 Describe the bulk preparation of dihydrogen by electrolytic method. What is the role of an electrolyte in this process ?

Dihydrogen is prepared by the electrolysis of acidified or alkaline water using platinum electrodes. Generally, 15 – 20% of an acid (

H_{2} S O_{4}

) or a base (NaOH) is used. Reduction of water occurs at the cathode as:

$2 H_{2} O + 2 e^{-} \to 2 H_{2} + 2 O H^{-}$

At the anode, oxidation of OH– ions takes place as:

$2 O H \to H_{2} O + \frac{1}{2} O_{2} + 2 e^{-}$

Therefore, Net reaction can be represented as:

$H_{2} O_{I} \to {H_{2}}_{(g)} + \frac{1}{2} O_{2_{(g)}}$

Electrical conductivity of pure water is very low owing to the absence of ions in it. Therefore, the electrolysis of pure water also takes place at a low rate. If an electrolyte such as an acid or a base is added to the process, the rate of electrolysis increases. The addition of the electrolyte makes the ions available in the process for the conduction of electricity and for electrolysis to take place.

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