A sample of nitrogen gas is collected over water at a temperature of 23 C. What is the pressure of the nitrogen gas if the atmospheric pressure is 742 mm Hg?

Answer
720.9 mmHg
Explanation
Gas collected over water must always account for the saturated vapor pressure.
Note that the saturated vapor pressure of water at 23 °C = 21.1 mm Hg.
Therefore atmospheric pressure is
[tex]Atmospheric\text{ }pressure=P_{SVP}-P_{nitrogen}[/tex]The atmospheric pressure given = 742 mmHg, Psvp = 21.1 mmHg, thus, we
[tex]\begin{gathered} 742mmHg=21.1mmH-P_{nitrogen} \\ \\ P_{nitrogen}=742mmHg-21.1mmHg \\ \\ P_{nitrogen}=720.9\text{ }mmHg \end{gathered}[/tex]