Question

The normal temperature range of the liquid phase of pure water is 0°C to 100°C. Which of the following solutions will have the largest temperature range for the liquid state?

A)	1 M aqueous acetic acid solution

B)	1 M aqueous magnesium sulfate

C)	1 M aqueous magnesium bromide solution

D)	1 M aqueous potassium bromide solution

E)	1 M aqueous ethanol solution

re water is 0°C to 100°C. Which of the following solutions will have the largest temperature range for the liquid state? 1 M aqueous acetic acid solution 1 M aqueous magnesium sulfate 1 M aqueous magnesium bromide solution 1 M aqueous potassium bromide solution 1 M aqueous ethanol solution

Answer 1

in order to have "largest temperature range" we must recall:

Apply Colligative properties

This is a typical example of colligative properties.

Recall that a solute ( non volatile ) can make a depression/increase in the freezing/boiling point via:

dTf = -Kf*molality * i

dTb = Kb*molality * i

where:

Kf = freezing point constant for the SOLVENT; Kb = boiling point constant for the SOLVENT;

molality = moles of SOLUTE / kg of SOLVENT

i = vant hoff coefficient, typically the total ion/molecular concentration.

At the end:

Tf mix = Tf solvent - dTf

Tb mix = Tb solvent - dTb

then

as seen, the more "i" we have, the more span will have the dT of both, boiling and freezing

therefore, choose an ionic compound with the most ions

KBr vs. MgBr2 vs. MgSO4

choose MgBr2 --< MG+2 + 2Br- = 3 ions

choose C