Suppose you are collecting a gas over water at 23 oC and obtain a pressure reading of 796.5 mm Hg.

Question

Suppose you are collecting a gas over water at 23 ^oC and obtain a pressure reading of 796.5 mm Hg.

If the vapor pressure of water is 21.1 mm Hg at the collection temperature, what is the pressure of the collected gas?

Answer 1

Applying Dalton's law of partial pressures — P_T = P_gas + P_H2O

P_gas = P_T - P_H2O

P_{H2O = vapor pressure of water at a given temperature, in this case 21.1 mmHg(given)}

P_{T (Total Pressure) = 796.55 mm Hg (given)}

So, P_gas = 796.55 mm Hg - 21.1 mm Hg = 775.5 mm Hg