Consider the following reaction to generate hydrogen gas: zn(s) + 2 hcl(aq) → zncl2(aq) + h2(g) the hydrogen gas is collected by displacement of water at 35.0 °c at a total pressure of 745 torr. the vapor pressure of water at 35.0 °c is 42 torr. calculate the partial pressure of h2 (in atm) if 353.2 ml of gas is collected over water from this method.

0.925 atm

Explanation:

By Dalton's Law, the total pressure of a gas mixture is the sum of the partial pressure of its components. The vapor pressure of the water is the pressure that some molecules that evaporated do under the liquid surface. The gas and the liquid are at equilibrium. So, the gas mixture is water vapor and hydrogen gas.

Ptotal = Pwater + PH₂

745 = 42 + PH₂

PH₂ = 703 torr

Transforming to atm:

1 atm 760 torr

x 703 torr

By a simple direct three rule

760x = 703

x = 0.925 atm

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