Calculate the mass of a non-volatile solute ( molecular mass `40`) which should be dissolved in `114 g` octane to reduce its vapour pressure to `80%`.

Options

A. `20`g
B. `30`g
C. `10`g
D. `40`g

Answer

C

Explanation

`P_(0)=100`, then p=`80`
`p=P_(0)x_(A)`
`80=100xxx_(A)`
`x_(A)=0.80`
`x_(A)=(n_(A))/(n_(A)+n_(B))=(114//114)/(114//114+w_(B)//40)`
`0.8=(1)/(1+w_(B)//40)`
`1+(W_(B))/(40)=(1)/(0.8)`
`w_(B)=10g`