Question

Which one of the following aqueous solutions will have the highest boiling point? Pleae provide workings.

Select 1:

a. 0.200 mol kg-1 KCl(aq)

b. 0.200 mol kg-1 Na3PO4(aq)

c. 0.200 mol kg-1 NH4NO3(aq)

d. 0.200 mol kg-1 Na2SO4(aq)

Answer 1

We have the eqution,

where, = elevation in boiling point

i = Van't Hoff Factor

m = molarity

K_b = molal elevation constant

Thus,

i m

Assume 100% dissociation

a) im(KCL) = 0.200 * i

KCL K ⁺ + Cl ^-

Here, i = 2

Therefore, im(KCL) = 0.4

b)  im(Na3PO4) = 0.200 * i

Na3PO4 3 Na⁺ + PO4 ^-3

Here, i = 4

Therefore, im(KCL) = 0.8

c) im(Na3PO4) = 0.200 * i

NH4NO3 NH4⁺ + NO3 ^-

Here, i = 2

Therefore, im(NH4NO3) =0.4

d) im(Na2SO4) = 0.200 * i

Na2SO4 2 Na ⁺ + SO4 ^2-

Here, i = 3

Therefore, im(Na2SO4) =0.6

Hence, greater the value of im, greater will be the value of elevation in boiling point so boiling point.

Therefore, 0.200 M Na3PO4 will have the highest boiling point.