A 250.0 mL flask of hydrogen gas is collected at 763 mm Hg and 35.0 Celsius by displacement of water from the flask. The vapor pressure of water at 35.0 Celsius is 42.2 mm Hg. How many moles of hydrogen gas are in the flask?
First, we need to calculate the partial pressure of the hydrogen gas in the flask. This can be done using the formula:
P(H2) = P(total) - P(H2O)
P(H2) = 763 mm Hg - 42.2 mm Hg
P(H2) = 720.8 mm Hg
Next, we need to convert the pressure from mm Hg to atm, since the ideal gas law uses atm as the unit of pressure:
1 atm = 760 mm Hg
720.8 mm Hg x (1 atm / 760 mm Hg) = 0.9484 atm
Now that we have the pressure of the hydrogen gas in atm, we can use the ideal gas law equation to calculate the number of moles of hydrogen gas present in the flask:
PV = nRT
(0.9484 atm) (0.250 L) = n (0.0821 L.atm/mol.K) (308.15 K)
0.2371 = 25.307 n
n = 0.00935 moles
Therefore, there are 0.00935 moles of hydrogen gas in the flask.