Question

A solid solution is made up of two solids 'A' and 'B'. Mass percentage of 'A' is 60% by mass in a solid solution. Find the molar mass of 'B', if the mole fraction of 'A' $\left(x_A\right)\text{is 0.20}$ and molar mass of 'A' is 100 g/mol.

• A. $16.67g$
• B. $35.50g$
• C. $40.66g$
• D. $25.33g$

Answer 1

The correct option is A $16.67g$

Taking 100 g of the solid solution,
Mass of A in the solution = 60 g
Mass of B in the solution = 40 g
$\text{Mole fraction of A}\left(x_A\right)=\frac{n_A}{n_A+n_B}=0.2$
By using mass - mole relationship, $\text{Number of moles}=\frac{Mass}{Molarmass}$
We get,
$x_A=\frac{\frac{60}{100}}{\frac{60}{100}+\frac{40}{M_B}}=0.2$
$\Rightarrow \frac{8}{M_B}=0.48$
$\Rightarrow M_B=16.67g$