Question

A compound of $X$ and $Y$ has an equal mass of them. If their atomic weights are $30$ and $20$ respectively. The molecular formula of that compound (its mol. wt. is $120$) could be:

• A. $X_2{Y}_2$
• B. $X_3{Y}_3$
• C. $X_2{Y}_3$
• D. $X_3{Y}_2$

Answer 1

Answer: (C)

$X_2{Y}_3$

Let the mass of $X$ be $30g$

Therefore, the mass of $Y$ will be $30g$

$\frac{molesofX}{molesofY}=\frac{30/30}{30/20}=\frac{1}{1.5}=\frac{2}{3}$

$X:Y=2:3$

$\therefore$ Empirical formula=$X_2{Y}_3$

Molecular weight of $X_2{Y}_3=2\times 30+3\times 20$

$=60+60$

$=120$

$\therefore$ The compound is $X_2{Y}_3$

Option $C$ is correct.