*Dalton’s Law** states that the **total pressure inside a container is obtained by** adding all the partial pressures of each non-reacting gas. *

$\overline{){{\mathbf{P}}}_{{\mathbf{total}}}{\mathbf{=}}{{\mathbf{P}}}_{\mathbf{Gas}\mathbf{}\mathbf{1}}{\mathbf{+}}{{\mathbf{P}}}_{\mathbf{Gas}\mathbf{}\mathbf{2}}{\mathbf{+}}{{\mathbf{P}}}_{\mathbf{Gas}\mathbf{}\mathbf{3}}{\mathbf{.}}{\mathbf{.}}{\mathbf{.}}}\phantom{\rule{0ex}{0ex}}{\mathbf{P}}_{\mathbf{total}}\mathbf{=}{\mathbf{P}}_{{\mathbf{H}}_{\mathbf{2}}}\mathbf{+}{\mathbf{P}}_{\mathbf{water}}\phantom{\rule{0ex}{0ex}}\mathbf{746}\mathbf{}\mathbf{mm}\mathbf{}\mathbf{Hg}\mathbf{=}{\mathbf{P}}_{{\mathbf{H}}_{\mathbf{2}}}\mathbf{+}\mathbf{23}\mathbf{.}\mathbf{78}\mathbf{}\mathbf{mm}\mathbf{}\mathbf{Hg}$

${\mathit{P}}_{{\mathbf{H}}_{\mathbf{2}}}\mathbf{=}$**722.22 mm Hg**

**Ideal gas equation: moles H _{2}**

$\frac{\mathbf{PV}}{\mathbf{RT}}\mathbf{=}\frac{\mathbf{n}\overline{)\mathbf{RT}}}{\overline{)\mathbf{RT}}}\phantom{\rule{0ex}{0ex}}\mathbf{n}\mathbf{=}\frac{\mathbf{PV}}{\mathbf{RT}}$

**mass = moles x molar mass **

A common way to make hydrogen gas in the laboratory is to place a metal such as zinc in hydrochloric acid (see the figure). The hydrochloric acid reacts with the metal to produce hydrogen gas, which is then collected over water. Suppose a student carries out this reaction and collects a total of 150.2 mL of gas at a pressure of 746 mmHg and a temperature of 25^{o}C. What mass of hydrogen gas (in mg) does the student collect? (The vapor pressure of water is 23.78 mmHg at 25^{o}C.)

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