Chlorine gas is collected in a gas collecting tube above water. The gas is at 20oC and the total pressure in the tube is 755 mmHg. What is the pressure (in mmHg) of chlorine gas in the tube?

Answer 1

Ptotal = pCl2 + pH2O
Look in your text for the vapor pressure of H2O at 20 C, substitute that for pH2O in the above and solve for pCl2. By the way, this ignores any loss of Cl2 due to dissolving in the water.