Water and chlorobenzene are immiscible liquids. Their mixture boils at `90^@`C under a reduced pressure of `7.82 xx 10^4` Pa. The vapour pressure of pure water at `90^@C` is `7.03 xx 10^4` Pa. On weight per cent basis, chlorobenzene in the distillate is equal to (mol. wt. of chlorobenzene is 112.5 g `"mol"^(-1)`)

Options

A. 50
B. 60
C. 70
D. 80

Answer

C

Explanation

`p_"mix"=7.82xx10^4` Pa
`p_(H_2O) + p_(C_6H_5Cl)=7.82xx10^4` Pa
`p_(H_2O) = 7.03xx10^4` Pa `therefore p_(C_6H_5Cl)=0.79xx10^4` Pa
`p prop n prop w/m , therefore (w_(C_6H_5Cl)xxM_(H_2O))/(w_(H_2O)xxM_(C_6H_5Cl))=p_(C_6H_5Cl)/p_(H_2O)`
`w_(C_6H_5Cl)/w_(H_2O)=(p_(C_6H_5Cl)xxM_(C_6H_5Cl))/(p_(H_2O)xxM_(H_2O))=((0.79xx10^4)xx112.5)/((7.03xx10^4)xx18)`=0.70
Weight per cent of chlorobenzene is distillate
`=0.70xx100` = 70