Question

An oxide of metal has 20% oxygen, the equivalent weight of oxide is:
(A) 32
(B) 40
(C) 48
(D) 52

Answer 1

The concept of equivalent weight tells us the exact amount of any substance actually participating in the activity. To solve the given type of question, we need to have a basic idea about the molecular mass of oxygen and the valency of the same which would be responsible for the calculation of equivalent weight.

Complete Solution :
Let us solve the given illustration by discussing some relevant topics needed for the same;
Equivalent weight-
This defines the actual weight of a substance which would combine with or displace one part by weight of hydrogen or eight parts by weight of oxygen; in general.

Now, moving towards the illustration,
We know from the definition too that the equivalent weight of oxygen is 8.
Given data-
Metal oxide has 20% oxygen i.e. we can say that 100 gm of metal oxide will contain 20 gm of oxygen and 80 gm of metal.
Now, by equivalence, to find the equivalent weight of metal we use:
$\dfrac{{{M}_{m}}}{{{M}_{o}}}=\dfrac{Eq.w{{t}_{m}}}{Eq.w{{t}_{o}}}$
where,
${{M}_{m}}$ = mass of metal
${{M}_{o}}$ = mass of oxygen
$Eq.w{{t}_{m}}$ = equivalent weight of metal
$Eq.w{{t}_{o}}$ = equivalent weight of oxygen

Therefore,
$\dfrac{80}{20}=\dfrac{Eq.w{{t}_{m}}}{8}$
$Eq.w{{t}_{m}}$ = 32 gm.
Thus, the equivalent weight of metal oxide will be the sum of the equivalent weights of oxygen and metal i.e. 8 + 32 = 40 gm.
So, the correct answer is “Option B”.

Note: Atomic weight is a dimensionless quantity whereas, equivalent weight has dimensions and units as well. It is usually determined by the experiments conducted but for numerical calculations, knowing molar masses of the substances we can calculate the equivalent weights.