Question

HCl gas is introduced at one end of the tube, and simultaneously NH3 gas is introduced at the other end. When the two gases diffuse through the cotton plugs down the tube and meet, a white ring appears due to the formation of NH4Cl(s). Why is this?

Answer 1

When the two gases are mixed, the ammonium chloride precipitates in the tube walls.

Step-by-step explanation:

This is the reaction:

HCl (g) + NH₃(g) → NH₄Cl (s) ↓

As the product formed is solid at room temperature, a suspension is first formed in the internal air of the tube that appears as a cloud. Afterwards it finally precipitates into the walls forming a white layer