Chemistry Question about Moles and Solutes

If one mole of each of these solutes is added to the same amount of water, which solution has the highest boiling point and lowest freezing point?

a) MgSO4
b) MgCl2
c) AlCl3
d) KI

The answer is the compound that produces the most ions per formula unit.

MgSO4 produces 2 ions: Mg+2 and SO4-2

MgCl2 produces 3 ions: Mg +2 and 2 Cl-

AlCl3 produces 4 ions: Al+3 and 3 Cl-

KI produces 2 ions: K+ and I-

The answer is AlCl3

The highest boiling point and lowest freezing point is determined by the total number of particles dissolved.

1 mol MgSO4 releases 2 mol of total particles -- 1 mol Mg2+ and 1 mol SO42-
1 mol MgCl2 releases 3 mol of total particles -- 1 mol Mg2+ and 2 mol Cl-
1 mol AlCl3 releases 4 mol of total particles -- 1 mol Al3+ and 3 mol Cl-
1 mol KI releases 2 mol of total particles -- 1 mol K+ and 1 mol I-

The solution of AlCl3 gives the lowest fp and highest bp because it releases the greatest number of particles.

The one that would produce the largest number of species in solution: AlCl3 which forms 4 components.