Question

The vapour pressure of pure liquids A and B are 300 and 880 mm Hg at 75 degree Celsius calculate the composition of the mixture such that it boils at 75 degree Celsius

Answer 1

Answer:

See below.

Explanation:

The vapour pressure of a binary solution is expressed as,

$p_{s}=x_{A}p^{0}_{A}+x_{B}p^{0}_{B}$

Which can be expressed as,

$p_{s}=x_{A}\left( p_A^{0}-p^{0}_{B}\right) +p^{0}_{B}$

For boiling, the vapour pressure of the solution must equal the atmospheric pressure ( 760 mm of Hg ),

$\begin{aligned} 760=x_{A}\left( 300-880\right) +880\\ -120=x_{A}\left( -580\right) \\ x_{A}=\dfrac {20}{580}=0.2\end{aligned}$

Therefore, mole fraction of B,

$x_{B}=1-x_{A}=1-0.2=0.8$