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?

Answer 1

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.