Collection of Gas Over Water
193 mL of O2 was collected over water on a day when the atmospheric pressure was 762 mmHg. The temperature of the water was 23.0 o C. How many grams of oxygen were collected?
- Use Dalton's law and the vapor pressure of water at 23.0 o C to correct the pressure to units of atmoshperes.
PT = Poxygen +Pwater
At 23.0 o C the vapor pressure of water is 21.1 mmHg. (This can be found on a vapor pressure table.)
762 mmHg = Poxygen + 21.1 mmHg
Poxygen = 762 mmHg - 21.1 mmHg
Poxygen =741 mmHg
- Convert the corrected pressure to atmospheres.
- Use the ideal gas law to find out how many moles of gas were produced:
PV = nRT
- Use the number of moles and the molecular weight of oxygen to find out how
many grams of oxygen were collected.