I'm having trouble understanding Boyle's Law and Dalton's law of partial pressures. Can anyone help me work this please? Thank you

Question

A sample of propane gas, C3H8, was collected over water at 22.5 ºC and 680. torr. The volume of the wet gas is 3.89 L. What will be the volume of the dry propane at standard pressure?

Answer 1

Ptotal = pC3H8 + pH2O
You know Ptotal is 680. Look up the vapor pressure of H2O in tables (from your text or otherwise), substitute and solve for pC3H8. That will be dry C3H8 at the conditions listed. Then use (P1V1/T1) = (P2V2/T2) to convert to standard conditions.