Wednesday problems

DALTON’S LAW OF PARTIAL PRESSURES
1. A 250.0 ml sample of oxygen is collected over water at 25 °C and 760.0 mmHg pressure. What is the pressure of
the dry gas alone? (736 mmgH)
2. A 32.0 ml sample of hydrogen is collected over water 20.0 °C and 750.0 mmHg pressure. What is the volume of the
dry gas at STP? (28.7 ml)
3. A 54.0 ml sample of oxygen is collected over water at 23.0 °C and 770.0 mmHg pressure. What is the volume of
the dry gas at STP? (49.1 ml)
4. A mixture of 2.00 mols of H2, 3.00 mols of NH3, 4.00 mols of CO2 and 5.00 mols of N2 exerts a total pressure of
1.053 atm. What is the partial pressure of each gas? (114 mmHg; 171 mmHg; 229 mmHg; 286 mmHg)
GRAHAM’S LAW OF EFFUSION
1. Under the same conditions of temperature and pressure, how many times faster will hydrogen effuse compared to
carbon dioxide? (4.7)
2. If the carbon dioxide from problem 5 takes 32 seconds to effuse, how long will the hydrogen take? (6.8sec)
3. What is the relative rate of diffusion of NH3 compared to He? Does NH3 effuse faster or slower than He? (.49,
slower)
4. If the He in problem 7 takes 20 sec to effuse, how long will NH3 take? (41sec)
5. An unknown gas diffuses .25 times as fast as He. What is the molar mass of the unknown gas? (64 g/mol)
VARIATIONS ON THE IDEAL GAS LAW CALCS
1. What is the molar mass of a gas if 0.427 g of the gas occupies a volume of 125 ml at 20.0 °C and 0.980 atm? (83.8
g/mol)
2. What is the density of a sample of ammonia gas, NH3, if the pressure is 0.928 atm and the temperature is 63.0 °C?
(.572 g/L NH3)
3. The density of a gas was found to be 2.0 g/L at 1.50 atm and 27 °C. What is the molar mass of the gas? (33g/mol)
4. What is the density of argon gas, Ar, at a pressure of 551 mmHg and a temperature of 25 °C? (1.18g/L Ar)
5. The density of dry air at sea level is 1.225 g/L at 15 °C. What is the average molar mass of the air? (29.0 g/mol