Question

A straight glass tube has 2 inlets, $x$ and $y$ at its two ends. HCl gas enters through inlet $x$ and $N{H}_3$ gas through inlet $Y$ at the same time and under identical conditions. The gases meet at a point P somewhere in the middle of the 200 cm long tube. The distance of point P from $x$ is:

• A. 118.9 cm
• B. 81.1 cm
• C. 91.1 cm
• D. 108.9 cm

Answer 1

The correct option is B 81.1 cm

Graham's law is what we will use here.
${\frac{\text{distance by HCl}}{\text{distance by NH}}}_3=\frac{r_{HCl}}{r_{N{H}_3}}=\sqrt{\frac{M_{N{H}_3}}{M_{HCl}}}=\frac{x}{200-x}$
$(\text{as rate}\propto \frac{1}{\sqrt{m}})$
$\therefore \frac{x}{200-x}=\sqrt{\frac{17}{36.5}}$
$\therefore 1.465x=200-x\Rightarrow x=81.13\text{cm}$