Question

Which metal is preferred for collecting hydrogen over steam? Write the balanced equation for the reaction.

Answer 1

To answer this question we should know about electrochemical series. The species which have less reduction potential then hydrogen can release hydrogen gas which can be collected over steam. The reduction potential is determined by electrochemical series.

Complete solution:
The elements are arranged according to their reduction potential in a series, this series is known as electrochemical series. Based on the reduction potential of an element we can tell the ease of reduction of an element.
The hydrogen lies in between the series. The elements having high reduction potential lies above the hydrogen in series and elements having low reduction potential lie below the hydrogen in the series.
The elements having low reduction potential will get oxidised and reduce the hydrogen of water to form hydrogen gas.
From the electrochemical series, we know the reduction potential of hydrogen is $0\,{\text{v}}$ and the reduction potential of iron is $- 0.45$v. so, the reduction potential of iron is lower than reduction potential of hydrogen so, iron will get oxidised and release hydrogen gas.
The balanced equation for the reaction of iron metal with steam is as follows:
${\text{3}}\,{\text{Fe}}\,{\text{ + }}\,{\text{4}}\,{{\text{H}}_{\text{2}}}{\text{O}}\, \to \,{\text{F}}{{\text{e}}_{\text{3}}}{{\text{O}}_{\text{4}}}\,{\text{ + }}\,{\text{4}}\,{{\text{H}}_{\text{2}}}$
Therefore, iron metal is preferred for collecting hydrogen over steam.

Additional information: By the chemical reaction, a gas is produced and collected. The collection method depends upon the two aspects:
The solubility of the gas
The density of the gas
The gases which are insoluble or very less soluble in water and are denser than air are collected over water. Hydrogen is non-polar gas, so it is insoluble in water, so it is collected over water. The gases which are denser than air and are soluble such as carbon dioxide and hydrogen chloride are collected by downward delivery. The gases which are less dense than air and are soluble such as ammonia are collected by upward delivery.

Note: Reduced means a species is accepting electrons, so the process is known as reduction. The process in which a species releases electrons is known as oxidation. An electrochemical series in which the elements are arranged with high reduction potential on top to low reduction potential on the bottom, then the species present above the hydrogen cannot release hydrogen gas and the species present below the hydrogen can release the hydrogen gas.