On mixing, heptane and octane form an ideal solution. At 373 K, the vapour pressures ofheptane and octane are 105 kPa and 45 kPa respectively. Vapour pressure of the solution obtained by mixing 25 g of heptane and 35 g of octane is very close to

Options

A. 144.5kPa
B. 72.0kPa
C. 36.1kPa
D. 96.2kPa

Answer

B

Explanation

`X_("heptane")= (25//100)/(25//100+ 35//114)=0.45`
`X_("octane")=1-0.45 = 0.55`
`P_("total.)= X_("heptane") xx P_("heptane") + X_("octane") xx P_("octane")= (105 xx 0.45 + 45 xx 0.55)= 72kPa`