# Problem: The hydrogen gas formed in a chemical reaction is collected over water at 30.0 oC at a total pressure of 734 mm Hg .If the total volume of gas collected is 724 mL , what mass of hydrogen gas is collected?

###### FREE Expert Solution

Dalton’s Law
at 30.0°C, water has a vapor pressure of 31.8 mmHg

${\mathbit{P}}_{{\mathbf{H}}_{\mathbf{2}}}\mathbf{=}$702.2 mmHg

Ideal gas equation: moles H2

$\frac{\mathbf{P}\mathbf{V}}{\mathbf{R}\mathbf{T}}\mathbf{=}\frac{\mathbf{n}\overline{)\mathbf{R}\mathbf{T}}}{\overline{)\mathbf{R}\mathbf{T}}}\phantom{\rule{0ex}{0ex}}\overline{){\mathbf{n}}{\mathbf{=}}\frac{\mathbf{P}\mathbf{V}}{\mathbf{R}\mathbf{T}}}$

mass = moles x molar mass

Molar mass of H2

H x 1.01 g/mol = 2.02 g/mol

###### Problem Details

The hydrogen gas formed in a chemical reaction is collected over water at 30.0 oC at a total pressure of 734 mm Hg .

If the total volume of gas collected is 724 mL , what mass of hydrogen gas is collected?