A sample of H2 is collected over water such that the combined hydrogen-water vapor sample is held at a pressure of 1 standard atmosphere. What is the partial pressure of the H2 if that of the water vapor is 2.5 kPa? Question 18 options: 2.5 kPa 101.3 kPa 98.8 kPa 103.8 kPa

The total pressure of a mixture of gases equals the sum of the partial pressures of the indiviudal gases in the sample.

So, combined hydrogen-water vapor pressure = partial pressure of H2 + partial pressure of water

Convert 1 atm to kPa: 1 atm = 101.325 kPa

=> 101.325 kPa = Partial pressure of H2 + 2.5 kPa

=> Partial pressure of H2 = 101.325 kPa - 2.5 kPa = 98.825 kPa

Answer: 98.8 kPa