Question

A metal oxide is reduced by heating it in a stream of hydrogen. It is found that after complete reduction, 3.15 g of the oxide have yielded 1.05 g of the metal. We may conclude that:
(A) Atomic mass of the metal is 4
(B) Atomic mass of the metal is 8
(C) Equivalent mass of the metal is 4
(D) Equivalent mass of the metal is 8

Answer 1

Equivalent weight is the mass of the equivalent. That is mass of a given substance which will combine with or displace a fixed quantity of another substance.
The equivalent weight of an element is the mass which combines with or displaces 1.008 gm of hydrogen or 8 g of oxygen or 35.5 g of chlorine.

Complete Step by Step Solution:
In the given question metal oxide is reduced by heating it in a stream of hydrogen metal oxide. This process reduces it to metal.
We can write it as
Metal oxide$+$Hydrogen$\to$Metal$+$Water
w.t. of oxide = 3.15 g w.t. of metal 1.05 g
(Since it is given that, 3.15 g metal oxide produces 1.05 g of metal.)
Let, the weight of metal oxide $(metal + oxygen)$ be ${W_1}$
$\Rightarrow {W_1} = 3.15\,g$
And let, the weight of metal be ${W_2}$
$\Rightarrow {W_2} = 1.05$
Thus, the weight of oxygen will be equal to $({W_1} - {W_2})$
$\therefore$ Weight of oxygen $= 3.15\,g - 1.05\,g = 2.10\,g.$
According to the definition of equivalent weight
Since 2.10 g of oxygen combines with 1.05 g of metal
$\therefore$ 8 g of oxygen combines with $= \dfrac{{1.05 \times 8}}{{2.10}}$
$= 4$ g of metal
$\therefore$ Equivalent mass of metal is 4.

**Therefore, the correct option is (C) Equivalent mass of the metal is 4

Additional information:**
If atomic weight is given. Then equivalent weight of compound is calculated by=atomic weight valency
For example, weight of oxygen molecule = 16 g
Valency = 2.
$\therefore$ Equivalent weight of oxygen $= \dfrac{{16}}{2} = 8.$
The atomic weight of helium is 4.002602.
Atomic weight is measured in amu (atomic mass unit) also called Dolton.

Note:
Atomic weight and equivalent weight of compound may or may not be the same. If there is one replaceable H-atom or $OH,$ then atomic weight and equivalent weight will be the same.
Example: Atomic weight of $HCL = 36.5$
And equivalent weight $= 36.5$
Atomic weight of ${H_2}S{O_4} = 98$
and equivalent weight $= \dfrac{{98}}{2}= 49.$