Question

The equivalent weight of NaOH is:
(A) 40
(B) 20
(C) 10
(D) 80

Answer 1

Equivalent weight is the quantity of a substance that would exactly react with the fixed quantity of another substance in the particular reaction.
Only one option will be correct from all the given options.

Complete answer:
Let us firstly see what we mean by equivalent weight;
Equivalent weight-
It is also known as the gram equivalent. This would basically mean the mass of a given substance that would combine with the fixed quantity of another substance.
Equivalent weights can be stated as;
$Eq.weight=\dfrac{Mol.mass}{Valency}$____ for simple reactions.
Or
$Eq.weight=\dfrac{Mol.mass}{Acidity}$____ for basic reactions.
Or
$Eq.weight=\dfrac{Mol.mass}{Basicity}$ _____ for acidic reactions.
The equivalent weights for the substance in a reaction can be calculated as the dissociation coefficient for that substance which divides the molecular mass of the same. It has the unit as mass specifically amu.
Illustration-
Molecular mass of NaOH = 40 gm/mol
The reaction for NaOH is given as,
$NaOH\to N{{a}^{+}}+O{{H}^{-}}$
Thus, by using above equations,
$Eq.weight=\dfrac{Mol.mass}{Acidity}$= $\dfrac{40}{1}=40$
Thus, the equivalent weight of NaOH is 40.

Therefore, option (A) is correct.

Note:
Do note that the equivalent weight of a substance may vary with the type of reaction it undergoes.
The number of equivalent weights of any substance dissolved in one litre of solution is called the normality of that solution. The number of equivalent weights or gram equivalents are given as the ratio of equivalent weight be the given mass of the substance i.e.
$n=\dfrac{eq.wt.}{given-mass}$