Question

Which of the following aqueous solutions has the highest boiling point.? Kb for water is 0.52 Celsius/m

a) 0.3 m potassium chloride

b) 0.4 m hydrofluroic acid

c) 0.2 m sodium sulfate

d) 0.2 aluminum nitrate

e) cannot be determined

Answer 1

Apply colligative properties

dTb = Kb*m*i

where

m = molality

i = vant hoff coefficient ( number of ions in solution)

Kb = 0.512 constant for water

so...

a) 0.3 m potassium chloride --> 0.3 * 2 ions = 0.6 effect

b) 0.4 m hydrofluroic acid --> 0.4 * 1.5 ions --> 0.6 approx, it won't dissociate 100%

c) 0.2 m sodium sulfate --> 0.2 * 3 ions = 0.6

d) 0.2 aluminum nitrate --> 0.2 * 4 ions = 0.8

e) cannot be determined

Clearly, from the list

choose Aluminium Nitrate since Al(NO3)3 --> Al+3 + 3NO3-