A sample of nitrogen gas is collected over
water at a temperature of 23°C. What is the pressure of the nitrogen gas if the atmospheric pressure is 791 mm Hg?
Answer in units of mm Hg
Ptotal = pN2 + pH2O
791 = Ptotal
pH2O--look up vapor pressure H2O at 23 C and substitute. Then solve for pN2.
To determine the pressure of the nitrogen gas, we need to consider the partial pressure of nitrogen and the vapor pressure of water at the given temperature.
The total pressure of the gas collected over water is the sum of the pressure exerted by nitrogen and the pressure exerted by water vapor. This is known as the "partial pressure" of nitrogen.
The vapor pressure of water increases with temperature. At 23°C, the vapor pressure of water is 21 mm Hg.
To calculate the partial pressure of nitrogen, we subtract the vapor pressure of water from the total pressure:
Partial Pressure of Nitrogen = Total Pressure - Vapor Pressure of Water
Partial Pressure of Nitrogen = 791 mm Hg - 21 mm Hg
Partial Pressure of Nitrogen = 770 mm Hg
Therefore, the pressure of the nitrogen gas is 770 mm Hg.