Question

In the laboratory preparation of dihydrogen, which of the following species is reduced?
A)${\text{Z}}{{\text{n}}^ + }$
B)${{\text{H}}^ + }$
C) Both A and B
D) None of these

Answer 1

Hint:
Dihydrogen is prepared in the laboratory by the reaction of zinc with either dilute sulphuric acid or hydrogen chloride. In both the reactions zinc is oxidized.

Complete step by step answer:
Hydrogen exists as a diatomic molecule called dihydrogen in normal state. It is the lightest substance known and it is lighter than air. Dihydrogen is prepared in a laboratory by two methods in which it reacts with acids and dihydrogen is produced. They are-
1.It is prepared by the reaction of granulated Zinc with dilute sulphuric acid. The reaction is as follows:
$ \Rightarrow {\text{Zn + }}{{\text{H}}_2}{\text{S}}{{\text{O}}_4} \to {\text{ZnS}}{{\text{O}}_4} + {{\text{H}}_2}$
Zinc sulphate is formed and dihydrogen is produced. Here \[{{\text{H}}^ + }\] ion gains electrons and is reduced to ${{\text{H}}_{\text{2}}}$and Zinc loses its electron to form zinc sulphate.
2. It is prepared by the reaction of granulated Zinc with dilute${\text{HCl}}$ .The reaction is as follows:
$ \Rightarrow {\text{Zn + 2HCl}} \to {\text{ZnC}}{{\text{l}}_2} + {{\text{H}}_2}$
Zinc chloride and dihydrogen are formed. Here \[{{\text{H}}^ + }\] ion gains electrons and is reduced to ${{\text{H}}_{\text{2}}}$and Zinc loses its electron to form zinc chloride.

Hence the correct option is B.

Additional Information
 In laboratory preparation method of dihydrogen-
1. Pure zinc is not used because its reaction with sulphuric acid is very slow .
2. Conc. sulphuric acid is not used because zinc reacts with concentrated acid to form sulphur dioxide gas instead of dihydrogen.

Note:
Dihydrogen is colourless, tasteless and odorless gas which is highly combustible. It is used in-
1. It is used as a reducing agent in the lab as it reduces heavy metal oxides to metal.
2. It is used as rocket fuel in the form of liquid hydrogen .
3. It is used in the manufacture of synthetic petrol.
4. It is used in atomic hydrogen torches and oxy hydrogen torches for cutting and welding.