The molar concentration of urea solution = Mol. wt. of urea 10g/dm3=6010M=61M Molar concentration of 5% nonvolatile solute = mol. wt. of non - volatile solute 50 g/dm3= m50M Both solutions are isotonic to each other; therefore, 61=m50 m=50×6=300 g mol−1 Caution 10 g per dm3 of urea is isotonic with 5% solution of a non-volatile solute. Hence, osmosis cannot occur between the two solutions. Thus, their molar concentrations are equal to each other.