Question

At 22.0 degrees Celsius , a student collects H2 gas in a gas collecting tube. The barometric pressure is 755.2mm Hg and the water levels inside and outside the tube are exactly equal. What is the total gas pressure in the gas collecting tube?

Answer 1

Total pressure is 755.2 as measured by the barometer. The total is composed of two partial pressures; i.e., that of the H2 gas + the water vapor at 22 C.
Ptotal = PH2 + PH2O. You can look up the vapor pressure of water in tables at various temperatures to find PH2O, then subtract from 755.2 to find the PH2 as a DRY gas (as opposed to the wet gas in the original problem.