Calculate mole fraction of ethanol and water in a sample of rectified spirit which contains 92% ethanol by mass.

Answer

`0.82`

Explanation

Mass of rectified spirit (ethanol + water) = 100 g (say)
`:.` Mass of ethanol = 92 g
Mass of water = (100 - 92) g = 8 g
Molar mass of ethanol
`C_(2) H_(5) OH = 46 g mol^(-1)`
`C_(2) H_(5) OH = 46 mol^(-1)`
`:. n_("ethanol ") = (92)/(46) ` mol = 2 mol
`n_("water ") = (8)/(18) ` mol = 0 . 44 mol
`x_("ethanol ") = (n_("ethanol"))/(n_("ethanol ") + n_("water"))`
`= (2 . 0)/( 2 . 0 + 0 . 44) = (2)/( 2 . 44) = 0 . 82 `