Diffusion — final check

1. describe / explain / predict

A sealed glass tube, 100 cm long, is full of still air. A small puff of a scented gas is let in at its left end. Four sensors, A to D, measure the concentration of the scented gas, all on the same scale (no units). The table gives each sensor's distance from the left end and two sets of readings. (a) Describe how the concentration along the tube changes between the two sets of readings. (b) Explain, using kinetic particle theory, why the concentration falls at sensor A but rises at sensor D. (c) Predict what all four sensors would read in the end, after a very long time. State whether the gas particles are still moving then.

(a) How the concentration along the tube changes

(b) Why the concentration falls at A but rises at D

(c) The readings in the end, and whether the particles are still moving

2. identify / deduce / explain

(Supplement) A teacher sets up a 50 cm ring tube with an unknown gas, Z, at the left end and hydrogen chloride (M_r 36.5) at the right end. Both plugs go in at the same moment, and both gases are at room temperature. The table shows where the white ring forms. (a) Which gas has the higher rate of diffusion? Use the measurements. (b) What can you deduce about the relative molecular mass of Z? (c) Explain, using particles, how the M_r of a gas affects its rate of diffusion. (d) Explain why both plugs must go in at the same moment.

(a) The gas with the higher rate of diffusion, and the evidence

(b) What you can deduce about the M_r of Z

(c) How M_r affects the rate of diffusion, using particles

(d) Why both plugs must go in at the same moment