Question

4 molar aqueous solution of urea has a density of 1.2 g/ml, the molality of
this solution is (Molecular mass of Urea = 60g mol-1)​

Answer 1

Answer:

4.2 or 4.17m

Explanation:

given:-

Molarity = M

M = density × %age × 10

Molecular weight

=> %age = M × Molecular weight

density×10

=> %age = 4×60/1.2×0.1 =20%

=> 20% of 1.2 gm solution = 20/100 × 1.2 = 0.24gm = wt. of solute.

=>wt. of solvent = wt. of solution - wt. of solute.

=>wt. of solvent = 1.2-0.24 = 0.96gm

molality(m) = wt. of solute × 1000

Molecular wt. × wt. of solvent

=> molality = 0.24 × 1000

60 × 0.96

=> molality = 4.167m

=> molality = 4.2m or 4.17m