Question

4. An ideal solution contains 40 mole percent of A and 60 mole percent of B at 80 oC. The vapor pressure of pure A and B at this temperature are 480 torr and 890 torr, respectively. Calculate the vapor pressure of the solution.

Answer 1

Answer :  The vapor pressure of the solution is, 726 torr.

Explanation : Given,

Mole percent of A = 40 %

Mole fraction of A = 0.4

Mole percent of B = 60 %

Mole fraction of A = 0.6

Now we have to calculate the partial pressure of A and B.

According to the Raoult's law,

$p_i=X_i\times p^o_i$

where,

$p_i$ = vapor pressure of gas

$p_^o_i$ = vapor pressure of pure gas  

$X_i$ = mole fraction of gas

$p_{A}=X_{A}\times p^o_A$

$p_{A}=0.4\times 480torr=192torr$

and,

$p_{A}=X_{A}\times p^o_A$

$p_{A}=0.6\times 890torr=534torr$

Now we have to calculate the vapor pressure of the solution.

$P_T=p_{A}+P_{B}$

$P_T=192torr+534torr$

$P_T=726torr$

Thus, the vapor pressure of the solution is, 726 torr.