A sample of nitrogen gas is collected overwater at a temperature of 23◦C. What is the pressure of the nitrogen gas if the atmospheric pressure is 744 mmHg?
Answer in units of mmHg.
Not sure of formula for this
A gas 'collected over water' is a mixture of water vapor and the gas. So
P,total = P,gas + P,water vapor
You'll solve for P,gas and to do that, you'll need data for vapor pressure of water at 23 C.
P,water vapor = 21.1 mm Hg (different sources may show different values)
Substitute:
744 = P,gas + 21.1
P,gas = ?
I guess I am dumb I don't get it
What don't you get? Dalton's law of partial pressures tells us that the total pressure of a system is the sum of the partial pressures of each gas. You have two gases in this system; i.e., N2 gas and water (as a vapor which is a gas). So according to Dalton's Law, the total pressure, which is given in the problem as 744 mm, is the total of the two pressures.
Ptotal = pH2O + pN2
Ptotal = 744 (from the problem)
pH2O = 21.1 (from a table)
pN2 = ?
To determine the pressure of the nitrogen gas collected over water, we need to take into account the partial pressure of water vapor in the air. The total pressure is the sum of the partial pressure of nitrogen gas and the partial pressure of water vapor.
To calculate the partial pressure of the nitrogen gas, known as the "dry" gas, we can use Dalton's law of partial pressures, which states that the total pressure is equal to the sum of the partial pressures of each gas in a mixture.
Dalton's law of partial pressures can be expressed as:
Total pressure = Pressure of nitrogen gas + Pressure of water vapor
In this case, the total pressure is given as 744 mmHg, and we need to calculate the pressure of the nitrogen gas. To isolate the pressure of the nitrogen gas, we subtract the pressure of water vapor from the total pressure:
Pressure of nitrogen gas = Total pressure - Pressure of water vapor
To calculate the pressure of water vapor, we can use the relationship between temperature and vapor pressure known as the Clausius-Clapeyron equation. However, for simplicity, we can use a commonly used approximation: the vapor pressure of water at 23°C is approximately 21 mmHg.
Substituting the values into the equation, we have:
Pressure of nitrogen gas = 744 mmHg - 21 mmHg
Therefore, the pressure of the nitrogen gas collected over water at a temperature of 23°C is approximately 723 mmHg.