A sample of nitrogen gas is collected over water at a temperature of 23.0°C. What is the pressure of nitrogen gas if atmospheric pressure is 785 mm Hg?

1 Answer
anor277
Aug 2, 2016

The saturated vapour pressure of water at 23 ""^@C is 21.1 mm Hg.

Explanation:

Gas collected over water must always account for the saturated vapour pressure. I have included a link to a Table, but in an exam these data would be supplied.

Thus "atmospheric pressure" = P_"SVP" + P_"dinitrogen"

P_"dinitrogen"=(785-21.1)*mm*Hg = 763.8*mm*Hg.

Note that when a gas is collecgted over water, we must always include P_"SVP".

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