Question

How to calculate the equivalent weight of ferrous ammonium sulphate?

Answer 1

As we know that equivalent weight (also called as gram equivalent) is the mass of one equivalent of a substance that is the mass of a given substance which will combine with or displace a fixed quantity of another substance in the reaction occurred.
Formula used: We will require the following formula in this solution:-

Complete answer:
Let us discuss about equivalent weight followed by the calculation of equivalent weight of ferrous ammonium sulphate as follows:-
-Equivalent weight: It is the quantity of a substance which exactly reacts with, or is equal to the combining value of an arbitrarily fixed quantity of another substance in a particular reaction that occurs. The substances react with each other in chemically equivalent proportions.
-Also the concept of equivalent weight has been displaced by that of molar mass as this is the mass of one mole of a substance. Hence the equivalent weight of an element is its gram atomic weight divided by its valence or number of electrons gained or lost in the reaction. Mathematically it can be represented as follows:-
$\text{Equivalent weight=}\dfrac{\text{Molecular mass}}{\text{Number of electrons gained or lost}}$
-Ferrous ammonium sulphate which is also known as Mohr’s salt is generally used in redox reaction and it occurs as follows:-
$F{{e}^{2+}}\to F{{e}^{3+}}+{{e}^{-}}$
Number of electron lost in the reaction = 1
Molecular mass of Ferrous ammonium sulphate = 392.13 g/mol
Hence the equivalent weight of Ferrous ammonium sulphate:-
$\begin{aligned} & \Rightarrow \text{Equivalent weight=}\dfrac{\text{Molecular mass}}{\text{Number of electrons gained or lost}} \\\ & \Rightarrow \text{Equivalent weight=}\dfrac{392.13g/mol}{1} \\\ \end{aligned}$
Equivalent weight = 392.13g/mol
-Hence, the equivalent weight of ferrous ammonium sulphate is 392.13g/mol.

Note:
-Remember that for any compound or molecule, if the n-factor is equal to 1 then the equivalent weight will always be equal to the molecular mass of that compound or molecule.
-Also equivalent weight concepts are very useful in calculations of concentration terms as well.