List the following solutions in order of decreasing freezing point: I. 0.040 mol kg−1 glycerin (a nonelectrolyte) II. 0.025 mol kg−1 Na2SO4 (assume complete dissociation in aqueous solution) III. 0.030 mol kg−1 KBr (assume complete dissociation in aqueous solution)

 0.040 mol glycerin > 0.030 mol KBr>  0.025 mol

Explanation:

Depression in freezing point:

where,

= freezing point of solution

= freezing point of solvent

= freezing point constant

m = molality

1. For 0.040 mol glycerin

, i= 1 as it is a non electrolyte and does not dissociate, concentration of ions will be

2. For 0.025 mol

, i= 3 as it is a electrolyte and dissociate to give 3 ions. and concentration of ions will be  

3. For 0.030 mol KBr

, i= 2 as it is a electrolyte and dissociate to give 2 ions, concentration of ions will be

Thus as concentration of solute is highest for , the depression in freezing point will be highest and thus freezing point will be lowest.

The order of decreasing freezing point: 0.040 mol glycerin > 0.030 mol KBr>  0.025 mol