# The vapour pressure of ethanol and methanol are 44.5 mm and 88.7 mm Hg respectively. An ideal solution is formed at the same temperature by mixing 60 g of ethanol with 40g of methanol. Calculate total vapour pressure of the solution.

Number of moles of ethanol =$\large\frac{60}{40}$$=1.5 Number of moles of methanol =\large\frac{40}{32}$$=1.25$
Let A = $CH_3OH, B = C_2H_5OH$, then
$X_A=\large\frac{1.25}{1.25+1.3}$$=0.4545$
$X_B=1-0.4545 = 0.545$
$P_T = X_AP_A^0 + X_B P_B^0$
$\Rightarrow 0.4545 \times 88.7 + 0.545 \times 44.5 = 40.31 + 24.27 = 64.58 mm 4g$