Question

When two cotton plugs, one moistened with ammonia and the other with hydrochloric acid, are simultaneously inserted into opposite ends of a glass tube that is 87.0 cm long, a white ring of NH₄Cl forms where gaseous NH₃ and gaseous HCl first come into contact. NH₃(g) + HCl(g) ⟶ NH₄Cl(s) At approximately what distance from the ammonia moistened plug does this occur? (Hint: Calculate the rates of diffusion for both NH₃ and HCl, and find out how much faster NH₃ diffuses than HCl.)

a) 52.2 cm
b) 34.8 cm
c) 17.4 cm
d) 69.6 cm

Answer 1

The white ring of NH4Cl forms closer to the ammonia moistened plug, at a distance of approximately b. 34.8 cm.

Step-by-step explanation:

To determine at what distance from the ammonia moistened plug the white ring of NH4Cl forms, we need to compare the rates of diffusion for gaseous NH3 and gaseous HCl. According to Graham's Law of Diffusion, the rate of diffusion is inversely proportional to the square root of the molar mass of the gas.

We can calculate the rate ratio by dividing the rate of diffusion of NH3 by the rate of diffusion of HCl. The rate ratio is equal to the square root of the molar mass ratio. Since the molar mass of NH3 is greater than the molar mass of HCl, NH3 diffuses slower than HCl.

Therefore, the white ring of NH4Cl will form closer to the ammonia moistened plug, and the approximate distance from the ammonia moistened plug where the white ring forms is about 34.8 cm (option b).