Question

The vapour pressure of water at $80^{\circ} C$ is $355.5\, mm$ of $Hg$. A $100\, mL$ vessel contains water saturated with $O _{2}$ at $80^{\circ} C ,$ the total pressure being $760\, mm$ of $Hg$. The contents of the vessel were pumped into a $50\, mL$ vessel at the same temperature. What is the partial pressure of $O _{2} ?$

• A. $1115 \,mm$
• B. $809 \,mm$
• C. $405\,mm$
• D. $3555\,mm$

Answer 1

Answer: (B)

$p_{\text {Total }}=p_{ H _{2} O }+p_{ O _{2}}$

$p_{ O _{2}}=760-355.5=404.5\, mm$

When the contents were pumped into $50 \,mL$ vessel

$P_{1}=404.5, V_{1}=100 \,mL , P_{2}=?, V_{2}=50 mL , P_{1} V_{1}=P_{2} V_{2}$

$P_{2}=\frac{404.5 \times 100}{50}=809\, mm$

Thus, $p_{ O _{2}}$ in $50\, mL$ vessel $=809\, mm .$