Question

The equivalent weight of a metal is $ 9g. $ What will be the molecular mass of its oxide?
(A) $ 4 $
(B) $ 54 $
(C) $ 102 $
(D) $ 113 $

Answer 1

Hint: We know that the 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.

Complete answer:
Equivalent weight has dimensions and units of mass, unlike atomic weight, which is dimensionless. It is determined by experiment, but now derived from molar masses. Additionally, the equivalent weight of a compound can be calculated by dividing the molar mass by the number of positive or negative electrical charges that result from the dissolution of the compound. 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.
Equivalent mass of the metal $ =9\text{ }g\text{ }e{{q}^{-1}} $
As given, the metal is trivalent which means it can lose up to three electrons to complete the octet, thus atomic mass of the metal $ =9\times 3=27\text{ }grams. $
Now the metal reacts with the oxygen it will most probably Metal $ \left( III \right) $ oxide and the following chemical reaction is carried out by; $ 4M+3{{O}_{2}}\to 2{{M}_{2}}{{O}_{3}} $
The Molar Mass of Metal Oxide $ = $ Atomic mass of the metal $ \times 2+ $ Atomic mass of the oxygen $ \times 3 $
Molar Mass of Metal Oxide $ =\left( 27\times 2 \right)+\left( 16\times 3\text{ } \right)=54+48\text{ }=102\text{ }grams. $
Therefore, the correct answer is option C.

Note:
Remember that 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 the hydrogen displacement method, the oxide method and the chloride method.