Question

Which of the following is laboratory preparation of dihydrogen?
A. \[3Fe + 4{H_2}{O_{(steam)}} \to F{e_3}{O_4} + 4{H_2}\]
B. \[2Na + 2{H_2}O \to NaOH + 2{H_2}\]
C. \[Ca{H_2} + 2{H_2}O \to Ca{(OH)_2} + 2{H_2}\]
D. \[Zn + {H_2}S{O_{4(dil.)}} \to ZnS{o_4} + {H_2}\]

Answer 1

Hint: Zinc granules are widely preferred for laboratory preparation of hydrogen gas because these granules usually have a small quantity of Cu, which has the ability to act as a catalyst in the given process.

Complete Step-by-Step Answer:
Dihydrogen or just Hydrogen is one of the most widely found gases. Various reactions release hydrogen gas as either a major product or as a by – product. But in most of these cases, the hydrogen gas formed is directly released into the atmosphere. It is very difficult to trap and collect the hydrogen formed because of its light weight and low density.
To collect this hydrogen, a very efficient laboratory method has been developed. The details about this process are as follows:

This process involves 4 major steps:
1. First of all, a certain amount of zinc granules is placed in a flask
2. After this, hydrochloric acid needs to be added to these zinc granules. This is done with the help of a thistle funnel. A replacement for hydrochloric acid could be sulphuric acid.
3. The reaction between the acid and the zinc granules would release hydrogen gas. The gas thus produced is transferred to a vessel filled with water, via a delivery tube.
4. The transferred hydrogen is now collected via a method known as downward displacement of water.
The chemical reaction for this process can be given as:
 \[Zn + {H_2}S{O_{4(dil.)}} \to ZnS{o_4} + {H_2}\]

Hence, Option D is the correct option.

Note: Before collecting the hydrogen gas with the help of the apparatus, precautions must be taken in order to ensure that all the air inside the apparatus has been displaced. This is because hydrogen gas reacts explosively with air.