Laboratory preparation of Hydrogen Gas

Hydrogen gas is prepared in laboratory by the action of dilute HCl upon granulated zinc.

Zn+dil⋅H2SO4⟶ZnSO4(aq)+H2↑

Note: This is a redox reaction since Zn is oxidized and H⁺ ions is reduced here.

Procedure:
The granulated zinc pieces are taken in a Woulfe’s bottle and the apparatus is fitted as shown in figure. The two necks of woulfe’s bottle is tighten up with cork so that no air enters from outside. It is connected with the delivery tube to a water trough containing water. Dilute sulphuric acid is poured slowly from the thistle funnel. Some crystals of copper sulphate are added to increase the rate of reaction. The hydrogen gas thus formed is collected in a gas jar through delivery tube by the downward displacement of water.

Laboratory preparation of Hydogen gas

Purification: The hydrogen gas thus obtained may contain different impurities like H₂S, NO₂, CO₂, moisture etc. So, these impurities are removed by using suitable process to get pure hydrogen.
Very pure hydrogen gas can be prepared in lab by the following reaction. This is a short and sweet method.

Mg+dil⋅H2SO4⟶MgSO4+H2↑