Question

A bottle of dry ammonia and a bottle of dry hydrogen chloride connected with a long tube are opened simultaneously at both ends. The white ammonium chloride ring first formed will be:

• A. At the centre of the tube
• B. Near the hydrogen chloride bottle
• C. Near the ammonia bottle
• D. Throughout the length of the tube

Answer 1

The correct option is B Near the hydrogen chloride bottle

When a bottle of dry $HCl$ and $N{H}_3$ are connected, $HCl$ and $N{H}_3$ react to form $N{H}_{4}Cl$, which is white in colour. The first white ring will be formed near the bottle which contains the gas that diffuses at a lesser rate than the other.

Using Graham's law of diffusion
Rate of diffusion is inversely proportional to the molecular weight of the gas i.e $r\propto M$

So, $\frac{r_{N{H}_3}}{r_{H}Cl}=\sqrt{\frac{M_{HCl}}{M_{N{H}_3}}}$

$HCl$ has a higher molecular weight than ammonia and so will diffuse at a lesser rate than ammonia. Hence the first ring will be formed near the $HCl$ bottle.