# A mixture of helium and neon gases is collected over water at 28.0°C and 745 mmHg. If the partial pressure of helium is 368 mmHg, what is the partial pressure of neon?

${P}_{\text{Total}}$ $=$ ${P}_{\text{He"+P_"Ne"+P_"SVP}}$
The partial pressures are additive; but to solve the problem we need 1 more parameter, ${P}_{\text{SVP}}$, the $\text{saturated vapour pressure}$, which is the $\text{vapour pressure}$ of water at the given temperature. ${P}_{\text{SVP}} = 18 \cdot m m \cdot H g$ at $301 \cdot K$.
From above, ${P}_{\text{Ne"=P_"Total"-P_"He"-P_"SVP}}$
$= \left(745 - 368 - 18\right) \cdot m m \cdot H g$ $=$ ??*mm*Hg.