Question

calculate molality of solution containing 20.7 gram of potassium carbonate in 500 ml of solution. The density of solution is 1 gm/ml.

Answer 1

We know that, molality= no.of moles/mass of solvent (in kg)
Molality= 20.7/138*1000/500
=0.3

Answer 2

Answer: Molality of solution is 0.31

Explanation: Molar mass of $K_2CO_3$ =  138 g/mole

20.7 gram of potassium carbonate in 500 ml of solution.

Density of solution= 1 g/ml

Now we have to calculate the mass of solution.

$Density=\frac{Mass}{Volume}$  

$Mass=Density\times Volume=1\times 500 ml=500g$

Mass of solution = Mass of solute + Mass of solvent

Mass of solvent= mass of solution - mass of solute= 500 - 20.7 = 479.3 g

Molality : It is defined as the number of moles of solute present per kg of solvent

Formula used :

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

where,

n= moles of solute

$Moles=\frac{\text{Given mass}}{\text{Molar mass}}=\frac{20.7}{138}=0.15moles$  

$W_s$ = weight of the solvent in g

Now put all the given values in the formula of molarity, we get

$Molality=\frac{0.15moles\times 1000}{479.3g}=0.31mole/kg$

Therefore, the molality of solution will be 0.31 mole/kg.