Collection of Gas Over Water

Problem:

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?

Strategy:

1. Use Dalton's law and the vapor pressure of water at 23.0 ^o C to correct the pressure to units of atmoshperes.
   P_T = P_oxygen +P_water
   
   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 = P_oxygen + 21.1 mmHg
   
   P_oxygen = 762 mmHg - 21.1 mmHg
   
   P_oxygen =741 mmHg
   
   
   
2. Convert the corrected pressure to atmospheres.
   
   
3. Use the ideal gas law to find out how many moles of gas were produced:
   PV = nRT
   
   
4. Use the number of moles and the molecular weight of oxygen to find out how many grams of oxygen were collected.
   
   
   
   
   

Show completed problem