Oxygen gas is collected over water at a temperature of 20c. If the totalmpressure of the system is 755mm, what is the pressure of the dry O2 gas?

Answer 1

vapor pressure H2O @ 20 C = ?. Look this up in tables in your text or notes. Call that pH2O
Then Ptotal = pH2O + pO2.
You know Ptotal and pH2O, solve for pO2.