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%`.

Explanation

`Ps=80%" of "P^(@)=0.80P^(@),MB=40g//mol`
`W_(A)=114g" "M_(A)=114g//mol" "n_(A)=(114)/(114)=1`
`(P^(@)-Ps)/(P^(@))=chi_(B)rArr(P^(@)-0.80P^(@))/(P^(@))=((WB)/(40))/((WB)/(4)+1)`
`0.2((WB)/(40)+1)=(WB)/(40)rArrWB=10g`