# A sample of nitrogen is collected over water at 20°C. The vapor pressure of water at 20°C is 18 mmHg. What is the partial pressure of the nitrogen if the total pressure is 21 mmHg?

Feb 26, 2017

${P}_{\text{total"=P_(N_2)+P_"SVP}}$
Now, we are given that ${P}_{\text{total}} = 21 \cdot m m \cdot H g$, and further that ${P}_{\text{SVP}}$, $\text{the saturated vapour pressure of water}$ at this temperature, $= 18 \cdot m m \cdot H g$.
So ${P}_{{N}_{2}} = {P}_{\text{total"-P_"SVP}} = \left(21 - 18\right) \cdot m m \cdot H g = 3 \cdot m m \cdot H g$.