In the laboratory method, for the preparation of hydrogen from granular zinc, why the concentrated H₂SO4, conc. HCl and HNO3 are not used?

In the laboratory method, for the preparation of hydrogen from granular zinc, why the concentrated H₂SO4, conc. HCl and HNO3 are not used?

31 January, 2022

Ans.

  1. Concentrated H₂SO4 is not used because a part of the acid gets reduced to sulfur dioxide.

H₂SO4 + H₂ ⟶ 2H₂O + SO2

 

  1. Hydrogen liberated by the action of conc. HCl on zinc will be impure, as it will contain fumes of volatile HCl. Also, ZnCl2 formed is insoluble in conc. HCl. So, it will form a coating on the zinc and the reaction stops after some time.

Zn + 2HCl ⟶ ZnCl2 + H₂ ↑

 

  1. HNO3 plays a double role. It can act as an acid and as an oxidizing agent. Hence, it is also not suitable. The best suitable acid is dilute HCl or dilute H₂SO4.