Question

Given,0.32 g of metal gave on treatment with an acid 112 mL of hydrogen at NTP. Calculate the equivalent mass of the metal.
(a)- 58
(b)- 32
(c)- 64
(d)- 24

Answer 1

Hint: The equivalent mass of the metal can be calculated by multiplying the mass of the metal into 11200 and then dividing it with the volume of hydrogen in mL. The formula of equivalent mass is $\text{Equivalent mass = }\dfrac{\text{mass of the metal x 11200}}{\text{Volume of hydrogen in mL}}$.

Complete answer:
The equivalent mass of an element or substance is calculated by dividing the atomic mass to the valency of the element.
$\text{Equivalent Mass = }\dfrac{\text{Atomic mass}}{\text{ valency}}$
But many times we don’t know the valency of the metal, so we cannot find the equivalent mass of the metal.
As we know that metals on reaction with acid liberates hydrogen gas. The method of hydrogen displacement is used to calculate the equivalent mass.
Here, some mass of metal reacts with acid to form hydrogen gas at NTP (normal temperature and pressure)
So, we can use the formula of multiplying the mass of the metal into 11200 and then dividing it with the volume of hydrogen in mL.
$\text{Equivalent mass = }\dfrac{\text{mass of the metal x 11200}}{\text{Volume of hydrogen in mL}}$
So, in the question the mass of the metal is $0.32\text{ g}$
And the volume of the hydrogen gas liberated at NTP (normal temperature and pressure) is $112\text{ mL}$
So, we can put these values in the above formula, we get
$\text{Equivalent mass = }\dfrac{\text{mass of the metal x 11200}}{\text{Volume of hydrogen in mL}}\text{ = }\dfrac{\text{0}\text{.32 x 11200}}{112}\text{ = 32}$
So, the equivalent mass of the metal is 32 g

Hence, the correct answer is an option (b)- 32.

Note:
There are several methods of finding the equivalent mass when the valency is not mentioned:
Oxide method: The formula used in the oxide method is:
$\text{Equivalent mass = }\dfrac{\text{Mass of the metal x 8}}{\text{Mass of Oxygen in the oxide}}$
Chloride method: The formula used in the chloride method is:
$\text{Equivalent mass = }\dfrac{\text{Mass of the metal x 35}\text{.5}}{\text{Mass of chlorine in the Chloride}}$