A sample of nitrogen is collected over water at 21 degrees Celsius at a pressure of 745 torr. What is the partial pressure, in torr, of the nitrogen?

Ptotal = pN2 + pH2O

Ptotal is 745.
pH2O = vapor pressure H2O. You can get this in tables in your text. Look for vapor pressure H2O at 21 C. I don't have these tables memorized but at 21 C it will be approximatly 18 or 19 torr.

To determine the partial pressure of nitrogen, we need to account for the pressure contribution of water vapor in the collected sample.

The partial pressure of nitrogen can be calculated using Dalton's law of partial pressures, which states that the total pressure of a mixture of gases is the sum of the pressures exerted by each individual gas.

Here's how to determine the partial pressure of nitrogen:

1. Find the vapor pressure of water at 21 degrees Celsius.
- Water's vapor pressure increases with temperature. At 21 degrees Celsius, the vapor pressure of water is approximately 19.8 torr.

2. Subtract the vapor pressure of water from the total pressure to obtain the partial pressure of nitrogen.
- Total pressure = 745 torr
- Vapor pressure of water = 19.8 torr
- Partial pressure of nitrogen = Total pressure - Vapor pressure of water
Partial pressure of nitrogen = 745 torr - 19.8 torr
Partial pressure of nitrogen ≈ 725.2 torr

Therefore, the partial pressure of nitrogen in the collected sample is approximately 725.2 torr.