Question

Very pure hydrogen (99.9%) can be made by which of the following processes?

• A. Reaction of methane with steam
• B. Mixing natural hydrocarbons with high molecular weight
• C. Electrolysis of water
• D. Reaction of salt like hydrides with water

Answer 1

The correct option is C Electrolysis of water

The pure hydrogen gas around 99.9% is prepared by electrolysis of water.
In electrolysis of water, the dissociation of the water molecule into hydrogen gas and oxygen gas is done by use of electric energy.
Reduction:
$2H_{2}O\left(l\right)+2e^{-}\to H_2\left(g\right)+2O{H}^{-}\left(aq\right)$
Oxidation :
$4O{H}^{-}\left(aq\right)\to O_2\left(g\right)+2H_{2}O\left(l\right)+4e^{-}$
In the oxidation reaction, oxygen atoms are oxidized and in reduction reaction, hydrogen atoms are reduced.
The oxidation reaction occurs at anode and the reduction reaction occurs at cathode.
The overall reaction can be given as:
$2H_{2}O\left(l\right)\to 2H_2\left(g\right)+O_2\left(g\right)$
Purest form of hydrogen is obtained by electrolysis
However, this method of production of hydrogen gas is very costly so it is not widely used. Currently, most of thr hydrogen is obtained from petrochemicals.