Question

A solution containing 30 g of non-volatile solute exactly in 90 g of water has a vapour pressure of 2.8 kPa at 298 K. Further, 18 g of water is then added to the solution and the new vapour pressure becomes 2.9 kPa at 298 K. Calculate: 

(i) molar mass of the solute 

(ii) vapour pressure of water at 298 K.

Answer 1

Suppose the molar mass of the solute = Mg mol^-1 

n₂ (solute) = \(\frac{30}{M}\) moles

Dividing equation (i) by equation (ii), we get

(ii) putting M = 23 in equation (i), we get