Question

2M urea solution is prepared. Density of the solution is 1.2gm/cc.
Find out molality

Answer 1

Given:

2M urea solution is prepared. Density of the solution is 1.2gm/cc.

To find:

Molality of solution?

Calculation:

2M urea means 2 moles of urea in 1 litre of solution.

$\rm 1) \: mass \: of \: urea = 2 \times 60 = 120 \: gm$

$\rm 2) \: mass \: of \: solution = 1000 \times 1.2 = 1200 \: gm$

So, mass of solvent (i.e. water)

$= 1200 - 120$

$= 1080 \: gm$

Now, molality will be :

$\rm molality = \dfrac{moles \: of \: solute}{mass \: of \: solvent \: ( in \: kg)}$

$\rm \implies molality = \dfrac{2}{1.08}$

$\rm \implies molality = 1.85 \: m$

So, molality is 1.85 m.