How many moles of gas exist for a volume of 0.125L collected over water at 298K at a pressure of 747mmHg?

1 Answer
May 2, 2016

You need the saturated vapour pressure. This shoud have been quoted with the question.

Explanation:

Gas collected over water is saturated with water vapour. At 298 K, the vapour pressure of water is 23.8mmHg.

So PGas collected = Pbutane+Pwater vapour

Pbutane = (74723.8)mmHg = 723.2mmHg.

n = PVRT = (723.2mmHg760mmHg)atm×0.125L0.0821LatmK1mol1×298K

5×103mol.