Adding a non-volatile solute in solvent, increases the boiling point of solvent. This is referred as elevation in boiling point. The increase in boiling point is mathematically expressed as
ΔTb = Kb X m ....... (1)
where, Kb = molal elevation constant = 0.51 oC/m
m = molality of solution = [tex] \frac{\text{weight of solute (g)}}{\text{Molecular weight X Weight of solvent (Kg)}} [/tex]
Given: weight of solute = 49.2 g
volume of solution = 500 ml
Density of water = 1 g/ml
∴ weight of solvent = 500 g = 0.5 kg
Also,we know that molecular weight of NaCl = 58.5
∴m = molality of solution = [tex] \frac{\text{49.2}}{\text{58.5 X 0.5}} [/tex]
= 1.68 m
The molality of solution is 1.68 m ...... (2)
Substituting 2 in 1 we get
ΔTb = Kb X m = 0.51 x 1.68 = 0.8568 oC
Thus, increase in boiling point of water is 0.8568 oC
Final boiling point of solution = 100 + 0.8565 = 100.8568 oC
