Question

What is $FeS{{O}_{4}}{{(N{{H}_{4}})}_{2}}S{{O}_{4}}6{{H}_{2}}O$
A. Mohr’s salt.
B. Green salt.
C. Alum.
D. Glauber’s salt.

Answer 1

Equivalent is the quantity that combines with or replaces $1g$ of hydrogen or $8g$ of oxygen. Molecular weight is the sum of the weight of the individual atoms of the molecule.

Complete step by step answer:
Equivalent weight can be defined as the one equivalent which is the mass of a given substance which combines with or replaces a fixed quantity of another substance. It is the mass of a substance that combines with or is chemically equivalent to one gram of hydrogen or eight grams of oxygen.
$FeS{{O}_{4}}$in the Mohr's salt, when used in a redox reaction gets oxidized to form $F{{e}_{2}}{{\left( S{{O}_{4}} \right)}_{3}}$
$F{{e}^{+2}}\to F{{e}^{+3}}$
The oxidation of Fe changes from $+2$ to $+3.$ The n-factor is the change in the oxidation state of any compound. Therefore, n-factor of Mohr's salt = change in oxidation state of Fe. Thus, $n-factor=1.$ The ferrous ion from Mohr’s salt gets oxidized and the manganese ion gets reduced. The pink color of potassium permanganate becomes colourless when the reduction of manganese ion occurs. Thus, potassium permanganate acts as a self-indicator. Mohr’s salt should be carefully handled because inhalation of Mohr’s salt causes irritation in the nose and throat. Ingestion of Mohr’s salt causes nuisance in mouth and stomach.
So, the correct answer is Option A.

Note: Students tend to understand the molecular weight and the equivalent weight of a compound as equal. But they are different from each other. Molecular weight is the sum of the weights of the individual atoms in the molecule whereas, the equivalent weight is molecular weight divided by the n-factor.