Question

Choose the aqueous solution below with the highest boiling point. These are all solutions of nonvolatile solutes and you should assume ideal van't Hoff factors where applicable.

A) 0.075 m NaI
B) 0.075 m (NH4)3PO4
C) 0.075 m NaBrO4
D) 0.075 m LiCN
E) 0.075 m KNO2

Answer 1

B. (NH₄)₃PO₄

Step-by-step explanation:

Elevation of boiling point is one of the colligative properties.

Formula is: ΔT = Kb . m . i

ΔT = Boiling T° of solution - Boiling T° of pure solvent.

i = Van't Hoff factor (numbers of ions dissolved)

Kb = Ebulloscopic constant

In this case, all the m are the same so let's dissociate the salts:

NaI → Na⁺ + I⁻ i = 2

(NH₄)₃PO₄ → 3NH₄⁺ + PO₄⁻³ i = 4

NaBrO₄ → Na⁺ + BrO₄⁻ i = 2

LiCN → Li⁺ + CN⁻ i = 2

KNO2 → K⁺ + NO₂⁻ i = 2

The biggest i would have the biggest boiling point, then B is the right answer, ammonium phosphate.

You count the i, with the moles of ions, you dissociate from the salt.