Question

100g solution of urea in water has 10g of urea.The molality of solution is

Answer 1

Answer : The molality of the solution is 1.84 m

Explanation :

Step 1 : Find moles of solute.

The solute in this case is urea. Let us find moles of urea.

$mol =\frac{grams}{Molar Mass}$

Molar mass of urea is 60.1 g/mol

We have 10 grams of urea.

Let us plug in these values to find moles.

$mol =\frac{10g}{60.1g/mol} = 0.166 mol$

We have 0.166 mol urea.

Step 2 : Find mass of solvent

Water is solvent here .

The mass of solution is given as 100 g.

Mass of solution = mass of solute + mass of solvent

100 g = 10 g + mass of solvent

mass of solvent = 100 g - 10 g = 90 g = 0.09 kg

Step 3 : Use molality formula

The molality of a solution is calculated using following formula

$m = \frac{(mol) Solute}{(kg) Solvent}$

$molality =\frac{0.166 mol}{0.09 kg}$

$molality = 1.84m$

The molality of the given solution is 1.84 m