Answer to Question #59228 in General Chemistry for Daniela

Question

Hydrogen gas produced by the reaction of zinc and hydrochloric acid was collected over water at 25 degrees Celsius. Barometric pressure is 742.5 mm Hg. What is the pressure of dry hydrogen gas if the vapor pressure of water at 25 degrees Celsius is 23.8 mm Hg?

Answer 1

When you collect a gas like H2 over H2O, the total pressure is due to the H2 plus a small amount of H2O vapor. So P H2(dry) = P total - P H2O = 742.5 mmHg - 23.8 mmHg = 718,7 mmHg or 718.7mmHg×(1atm/760atm)=0.945atm