Question

Dry nitrogen gas is bubbled through liquid benzene (C₆H₆) at 20.0⁰C. From 100.0L of the gaseous mixture of nitrogen and benzene, 24.7 g of benzene is condensed by passing the mixture through a trap at a temperature where nitrogen is gaseous and the vapor pressure of benzene is negligible. What is the vapor pressure of benzene at 20.0⁰C?

Short answer

The vapor pressure of benzene at 20.0⁰Cis 577.6 torr.

Step-by-step solution

Determine the moles of benzene:

The number ofmolespresent inbenzene:

$$\begin{gathered} n=\frac{\text{mass}}{\text{molecular mass}} \\ n=\frac{24.7g}{78.11g/mol} \\ n=0.316mol \end{gathered}$$

Determine the vapor pressure of benzene at 20.00C.

For ideal gas: pV = nRT

$$\begin{gathered} p\times 100L=0.316mol\times 0.0821Latm/Kmol\times 293K \\ p=\frac{0.316mol\times 0.0821Latm/Kmol\times 293K}{100L} \\ p=\frac{0.76atm}{1atm}\times 760torr \\ p=577.6torr \end{gathered}$$

Hence the vapor pressure is577.6 torr.