Question

A gas mixture has 2 atm `He`, 4.8 atm `Xe`, and 1.9 atm `O_2`. Which gas takes up the most volume in a total of 456 mL?

Answer 1

Interesting question, and I think your examiner is trying to be malicious. The answer required is that ALL the gases occupy equal volume.

Explanation:

Dalton's law of partial pressure clearly states that in a gaseous mixture, the pressure exerted by a component is the same as the pressure it would exert if it ALONE occupied the container.

So, given the above, to ask which gas occupies the most volume is a non-sequitir. All the gases occupy an equal volume, and, as stated, this volume is `456*mL`. The total pressure is of course `(2+4.8+1.9)*atm`, but this is not what the question asked.

PS I actually like this question, so I am going to steal it for my A2 class as a concept type of question to establish Dalton's Law. I bet it will fool most of the little blighters.