Question

When water is electrolyzed, hydrogen and oxygen are produced in the ratio 2:1. Why?

Answer 1

Electrolysis is a chemical technique that uses direct current to drive a nonspontaneous chemical reaction. This technique is commonly used to separate the elements from naturally occurring sources like ores etc.

Complete answer:
The chemical reaction for the synthesis of water can be given as:
$2{H_2} + {O_2} \to 2{H_2}O$
We can see from the reaction that 2 moles of Hydrogen and 1 mole of oxygen are needed to produce 2 moles of water. Hence the ratio of the reactants are 2:1. In the molecule of water also there are two hydrogen atoms and 1 oxygen atom making the ratio again 2:1.
We know that pure water is a poor conductor of electricity, therefore we add an impurity such as salt or acid to make it conduct. When current is passed through the water it splits into Hydrogen and Oxygen. Hydrogen is liberated at the cathode and oxygen is liberated at the anode.
An Electrical source is connected between two electrodes or two plates which are placed in water. The amount of hydrogen liberated is double the amount of oxygen liberated. The dissociation of water can be given by the equation: $2{H_2}O \to 2{H_2}(g) + {O_2}(g)$
Here also the mole ratio in which hydrogen and oxygen are liberated is 2:1, the same is found in the molecule of water also.

Note:
This process of electrolysis of water is used in the hydrogen fuel cells, where Hydrogen gas is required to drive the vehicles and motors. This technique is also used in rockets, in space stations, to generate oxygen which acts as a fuel.