Answer:
P = 746.2 mmHg or 0.9818 atm
Explanation:
First, we have a sample gas (This can be hydrogen, argon, nitrogen or any other gas) that was collected with a pressure of 778 mmHg. We also know the vapor pressure which is 31.8 mmHg. To get the pressure that the gas is exerting, we can assume that the atmospherical pressure is the total pressure of the whole system. Therefore we can use the following expression:
Pt = Pw + Pg (1)
Where:
Pt: total pressure
Pw: water pressure
Pg: gas pressure
From (1) we can solve for the gas pressure and have:
Pg = Pt - Pw
Replacing the data we have:
Pg = 778 - 31.8
Pg = 746.2 mmHg
This would be the pressure of the gas
If you want this value in atm, you should divide it by 760 mmHg (Conversion from mmHg to atm):
Pg = 746.2 / 760
Pg = 0.9818 atm