A sample of hydrogen is collected over water at a total pressure of 648 mm Hg at 22 oC. The vapor pressure of water at 22 oC is 19.8 mm Hg. The partial pressure of the hydrogen is __________.

Ptotal = pH2O + pH2

To find the partial pressure of hydrogen, we need to subtract the vapor pressure of water from the total pressure.

Partial pressure of hydrogen = Total pressure - Vapor pressure of water

In this case, the total pressure is given as 648 mm Hg and the vapor pressure of water at 22 oC is given as 19.8 mm Hg.

Partial pressure of hydrogen = 648 mm Hg - 19.8 mm Hg

Partial pressure of hydrogen = 628.2 mm Hg

Therefore, the partial pressure of hydrogen is 628.2 mm Hg.