Hydrogen gas produced in the laboratory by the reaction of zinc and hydrochloric acid was collected over water at 25°C.The barometric pressure at the time was 742.5 mm Hg.What is the pressure of dry hydrogen gas if the vapor pressure of water at 25°C is 23.8 mm Hg?

Question

Quizplus · Accepted Answer

The pressure of dry hydrogen gas can be calculated using the formula: 
P(H2) = P(total) - P(H2O vapor) 
where P(total) is the total pressure of the gas collected over water (742.5 mm Hg), and P(H2O vapor) is the vapor pressure of water at 25°C (23.8 mm Hg). 
Thus, 
P(H2) = 742.5 - 23.8 = 718.7 mm Hg 
Therefore, the answer is choice B.

Hydrogen Gas Produced in the Laboratory by the Reaction of Zinc