Question

Arrange the following solutions in order of increasing boiling point elevation and then provide an explanation for your arrangement. 0.50 m KCl; 0.5 m C6H6O6; 0.5 m Fe(NO3)3; 0.5 m Na2SO4.

Answer 1

Here m means molality.

To arrange these compounds, first, we must know this:

ΔTb = Kb x m x i

ΔTb = boiling point elevation

kb = 0.52 ºC/m for water (solvent) we assume that our solvent is water, the same for the 4 solutions between solutes and water.

m = the same for the 4 of them

i = Van't Hoff factor = number of particles into which the solute is dissociated.

"i" will change for all the cases.

For 0.50 m KCl)

KCl ==> k+ + Cl-, so i = 2 (2 ions)

For 0.5 m C6H6O6)

i = 1 (C6H6O6 doesn't dissociate)

For 0.5 m Fe(NO3)3)

Fe(NO3)3 ===> Fe+3 + 3 NO3-

i = 4 (4 ions)

For 0.5 m Na2SO4)

Na2SO4 ==> 2 Na+ + SO4-2

i = 3

According to ΔTb = Kb x m x i, the only factor that changes is "i", so it will give the order of increasing boiling point elevation of these compounds:

Answer:

0.5 m C6H6O6 < 0.50 m KCl < 0.5 m Na2SO4 < 0.5 m Fe(NO3)3