Question

The equivalent weight of a certain trivalent element is 20. Molecular weight of its oxide is:
A.152
B.56
C.168
D.68

Answer 1

Equivalent weight of a solution is defined as the molecular weight of the solute divided by the valence of the solute. It is used for predicting the mass of a substance that reacts with one atom of hydrogen in an acid-base analysis like in titration.
Formula used:
Atomic mass of the element$=$equivalent mass of the element$\times$valency

Complete step by step answer:
Basically, the weight in atomic mass units of each of the atoms in a given formula is the molecular weight of the substance whereas the equivalent weight of a solution is defined as the molecular weight of the solute divided by the valence of the solute.
Now, in the given question, the equivalent weight of a trivalent element is 20.
So, according to the formula, the atomic weight of the molecule will be:
Atomic weight$=$equivalent mass of the element $\times$valency
$= 20 \times 3$
$= 60gmo{l^{ - 1}}$
Now, the oxide can be represented as ${E_2}{O_3}$ where E represents the element.
Now, the atomic weight is known to us, so we can calculate the molecular weight of the oxide.
Therefore, the atomic weight of the oxide is:
$=$ $2(60) + 3(16)$
$= 168$ $= 168gmo{l^{ - 1}}$

Hence, option C is correct.

Note:
Sometimes if the valency of the atom is not known, then there are various different methods to determine the equivalent mass of an element. Some of the methods are hydrogen displacement method, oxide method and chloride method.