Question

Derive an expression for the determination of molecular mass of a solute on the basis of osmotic pressure.

Answer 1

van’t Hoff equation can be written as

πV = nRT    ...(i)

If w grams of a solute are dissolved in V litres of a solution and M' is the molecular mass of the solute, we have

`n = w/(M^')`

Putting the value of n in Eq. (i) (van’t Hoff equation), we have

`piV = w/(M^') RT`

or `M^' = (wRT)/(nV)`