Question

Which salt would raise the boiling point of a solvent the most?

a. 1.4 m Na2SO4

b. 4.0 m CH3OH

c. 1.4 m NaCl

d. 1.0 m CaCl2

The answer should be a but could someone explain why?

Answer 1

ΔTb = i*Kb*m

ΔTb is the elevation in boiling point

ΔTb will be maximum when i*m is maximum

Boiling temperature is maximum when ΔTb will be maximum

i is the number of ions that a compound can break into

1)

Na2SO4 will dissociate into 2 Na+ and 1 SO42-

i = 3

so,

i*m = 3*1.4 = 4.2

2)

CH3OH

It doesn’t dissociate

i = 1

i*m = 1*4.0 = 4.0

3)

NaCl

i=2

i*m = 2*1.4 = 2.8

4)

i=3 because it is non electrolyte

i*m = 3*1.0 = 3.0

i*m is maximum for a

So, a is the answer

Answer: a