If the total volume of gas collected is 724 mL, what mass of hydrogen gas is collected

given:
The hydrogen gas formed in a chemical reaction is collected over water at 30.0 deg C at a total pressure of 732 mm Hg.

Part A:What is the partial pressure of the hydrogen gas collected in this way?
answer is 700 mm Hg.

Part B:
If the total volume of gas collected is 724 mL, what mass of hydrogen gas is collected?
I don't know what to do here, please help

according to : http://antoine.frostburg.edu/chem/senese…
when a gas is collected over water at 30.0 deg C , the H2O vapor pressure is 32 Torr


Part A:What is the partial pressure of the hydrogen gas collected in this way?
at a total pressure of 732 mm Hg. - 32 Torr H2O vapor = 700. Torr H2
your answer is
answer is 700 mm Hg.



Part B:
If the total volume of gas collected is 724 mL, what mass of hydrogen gas is collected?
find moles
PV = nRT
(700.Torr)(0.724 Litres) = n (62.36 Torr-Litres/mol-K) (303 Kelvin)
n = 0.02682 moles of H2

using molar mass, find moles:
( 0.02682 moles of H2) (2.016 grams H2 / mol) = 0.05407 grams of H2

your answer rounded to 3 sig figs is
0.0541 grams of H2