Question

A mixture of $O_2$ and gas $Y$ (mol. wt. $80$) in the mole ratio $a:b$ has a mean molecular weight $40$. What would be mean molecular weight, if the gases are mixed in the ratio $b:a$ under identical conditions? (Gases are non-reacting)

• A. $40$
• B. $48$
• C. $62$
• D. $72$

Answer 1

The correct option is A $40$

$\text{Given,}40=\frac{a\left(32\right)+b\left(80\right)}{a+b}\left[\begin{array}{c}\because 40a+40b=32a+80b\\ 8a=40b\\ a=5b\end{array}\right]x=\frac{b\left(32\right)+a\left(80\right)}{a+b}=\frac{32b+400b}{6b}=\frac{432}{6}=72\Rightarrow \text{The mean molecular weight = 72 gm}$