How will you calculate the molecular mass of a solute with the help of relative lowering in vapour pressure of a solution of a non volatile solute?

Explanation

We know that the relative lowering of V.P. is equal to the mole fraction of the solute
`(Delta p)/( p_(A)^(@)) = x_(B)`
`(Delta p)/(p_(A)^(@)) = ( n_(B))/( n_(A) + n_(B))`
If solution is dilute ` n_(A) gt gt gt n_(B) rArr n_(A) + n_(B) ~~ n_(A)`
`(Delta p)/( p_(A)^(@)) = (W_(B)// M_(B))/(W_(A)// 18)" "` [Mol. mass of water = 18]
Knowing `Delta p` (decrease in V.P.). ` p_(A)^(@)` (V.P. of pure A at that temperature ) `W_(B)` (mass of solute ) `W_(A)` (mass of water ) `M_(B) ` (mol. mass of solute) can be calculated.