A sample of O2 gas is collected over water at 25oC at a barometric pressure of 751 torr. The vapor pressure of water at 25oC is 23.8 torr. What is the partial pressure of the O2 gas in the sample

727.7 torr

Explanation:

Since the gas was collected over water, it is likely to be saturated with water vapour and the total pressure is given as;

Ptotal = Pgas + Pwater

From the question;

Ptotal = 751 torr

Pgas = ?

Pwater = 23.8 torr

Making Pgas subject of equation, we have;

Pgas = Ptotal - Pwater

Pgas = 751 torr - 23.8 torr

Pgas = 727.7 torr

it's all four options.