Calculate the mass of a non-volatile solute (molar mass 40 g `mol^(-1)`) which should be dissolved in 114g octane to reduce its vapour pressure to 80%.

Answer

`10g`

Explanation

`p^(@)=100,p_(S)=80`
`W_(1)=114g`
`n_(1)=(114)/(114)=1 (Mw` or octane `=114)`
`(p^(@)-p_(S))/(p^(@))=(20)/(100)=(n_(2))/(n_(1)+n_(2))=(W_(2)//40)/(1+(W_(2)//40))`
`(1)/(5)(1+(W_(2))/(40))=(W_(2))/(40)`
`W_(2)=10g`