Question

1.35 g of X element is completely converted to 1.88 g compound XO. What is the atomic weight of X?
A. 20.32
B. 40.64
C. 16.25
D. 56.10

Answer 1

Hint: There is a formula to calculate the equivalent weight of metal from its molecular formula (oxide of the element) and it is as follows.
\[\text{Equivalent weight of metal=}\dfrac{\text{Mass of the metal}}{\text{Mass of the oxygen}}\text{ }\!\!\times\!\!\text{ 8}\]
By using equivalent weight we can calculate the atomic weight of the compound.

Complete Solution :
- In the question it is given that 1.35 g of X element is completely converted to 1.88 g compound XO.
- We have to find the atomic weight of the compound.
- The given mass of the metal X is 1.35 g.
- The given mass of the compound is XO is 1.85.
- The mass of the oxygen will be = 1.85 – 1.35 = 0.5 g.
- That means 0.5 g is the mass of the oxygen which is present in XO.
- Substitute all the known values in the below formula to calculate the equivalent weight of the metal.
\[\begin{align}
  & \text{Equivalent weight of metal=}\dfrac{\text{Mass of the metal}}{\text{Mass of the oxygen}}\text{ }\!\!\times\!\!\text{ 8} \\
 & =\dfrac{1.35}{0.5}\times 8 \\
 & =20.32 \\
\end{align}\]
- The equivalent weight of the compound XO is 20.32.
- We know that the valence of the metal in XO is 2.
- Then by multiplying the valence of the metal with its equivalent weight we will get the atomic weight of X.
- Therefore atomic weight of X = (20.32) (2) = 40.64.
- Therefore the atomic weight of the X is 40.64.
So, the correct answer is “Option B”.

Note: The product of valence of the metal and equivalent weight of the metal gives the atomic weight of the metal and we can write it as a formula and it is as follows.
Atomic weight of the metal = (Equivalent weight of the metal) ( Valence of the metal it the compound)