How many grams of hydrogen are collected in a reaction where 1.80L of hydrogen gas is collected over water at a temperature of 40degrees C and a total pressure of 738torr?

Answer 1

Use PV = nRT
Remember T must be in kelvin.
Look up vapor pressure H2O at 40 C.
Substitute [(738-vpH2O)/760] for P and solve for n = number of mols. Then n = grams/molar mass. You know n and molar mass, solve for grams.