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

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Answer 1 · 2016-05-02T19:41:33

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

Gas collected over water is saturated with water vapour. At $298$ $K$ , the vapour pressure of water is $23.8*mm*Hg$ .

So $P_"Gas collected"$ $=$ $P_("butane") + P_("water vapour")$

$P_("butane")$ $=$ $(747-23.8)*mm*Hg$ $=$ $723.2*mm*Hg$ .

$n$ $=$ $(PV)/(RT)$ $=$ $(((723.2*mm*Hg)/(760*mm*Hg))*atmxx0.125*L)/(0.0821*L*atm*K^-1*mol^-1xx298*K)$

$~=$ $5xx10^-3*mol$ .

How many moles of gas exist for a volume of 0.125*L0.125*L collected over water at 298*K298*K at a pressure of 747*mm*Hg747*mm*Hg?