Question

mole fraction of Uria in an aqueous solution is 0.1.If density of solution is 2gm/ml calculate the Molarity and Molality of solution.

Answer 1

Answer: Molarity of solution is 9.0 M and molality is 6.2 m

Explanation:

Molarity of a solution is defined as the number of moles of solute dissolved per Liter of the solution.

$Molarity=\frac{n\times 1000}{V_s}$

where,

n= moles of solute

 $V_s$ = volume of solution in ml

Molality of a solution is defined as the number of moles of solute dissolved per kg of the solvent.

$Molality=\frac{n\times 1000}{W_s}$

where,

n = moles of solute

$W_s$ = weight of solvent in g

Mole fraction of urea is = 0.1, i.e. 0.1 moles of urea is present in 1 mole of solution.

Moles of solute (urea) = 0.1

moles of solvent (water) = 0.9

weight of solvent =$moles\times {\text {Molar mass}}=0.9\times 18=16.2 g$

weight of solute=$moles\times {\text {Molar mass}}=0.1\times 60=6g$

weight of solution = 16.2+6= 22.2 g

Volume of solution=$\frac{\text {mass of solution}}{\text {density of solution}}=\frac{22.2g}{2g/ml}=11.1ml$

1. Molarity = \frac{n\times 1000}{V_s}=\frac{0.1\times 1000}{11.1}=9.0M[/tex]

2. Molality = \frac{n\times 1000}{W_s}=\frac{0.1\times 1000}{16.2}=6.2m[/tex]