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LEAALIBEGIN
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The vapor pressure of benzene at 25 °C is 95.1 mm Hg and of toluene 28.4 mm Hg. The mass fractions of benzene and toluene in a solution are 0.5.
a) Calculate the partial pressure of benzene and toluene above the solution.
b) Calculate the total vapor pressure above the solution.
c) Calculate the vapor composition above the solution.

Answer :

Benzene be B

Toluene be T

We have made then one lettered to make things easier

  • [tex]\sf P^0_B=95.1mmHg,P^0_T=28.4mmHg[/tex]
  • [tex]\sf x_B=x_T=0.5[/tex]

[tex]\\ \rm\Rrightarrow \dfrac{P^0_B-P_B}{P^0_B}=x_B[/tex]

[tex]\\ \rm\Rrightarrow 95.1-P_B=95.(0.5)[/tex]

[tex]\\ \rm\Rrightarrow 95.1-P_B=47.55[/tex]

[tex]\\ \rm\Rrightarrow P_B=47.55mmHg[/tex]

And

[tex]\\ \rm\Rrightarrow \dfrac{P^0_T-P_T}{P^0_T}=x_T[/tex]

[tex]\\ \rm\Rrightarrow 28.4-P_T=28.4(0.5)[/tex]

[tex]\\ \rm\Rrightarrow P_T=14.2mmHg[/tex]

Total vapour pressure

  • 28.4+95.1
  • 123.6mmHg

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