Question

Which of the following aqueous solutions has the highest freezing point 0.6m fructose 0.3m CaCl2 0.1m Al2(SO4)3 0.2m Mg3(PO4)2

Answer 1

• The freezing point is directly proportional to the van't Hoff factor(i) and molality(m).

  $\Delta T_f\alpha i\times m$

• Higher the i(van't Hoff), more freezing point is depressed or lower is the freezing point and vice verse.

1. Fructose​ is non-electrolyte, i=1 and m=0.6 hence,

$\Delta T_f\alpha 1\times 0.6=0.6$

2. $CuC{l}_2$ is electrolyte, contains 3 ions in it one copper ion and two chloride ion, i=3, m=0.3

$\Delta T_f\alpha 3\times 0.3=0.9$

3. $A{l}_2{\left(S{O}_4\right)}_3$ is electrolyte, contains 5 ions in it two aluminum ion and three sulfate ion, i=5, m=0.1

$\Delta T_f\alpha 5\times 0.1=0.5$

4. $M{g}_3{\left(P{O}_4\right)}_2$ is electrolyte, contains 5 ions in it three magnesium ion and two phosphate ion, i=5, m=0.2

$\Delta T_f\alpha 5\times 0.2=1.0$

Hence, the lowest $\Delta T_f$ is for $A{l}_2{\left(S{O}_4\right)}_3$ and so it has the highest freezing point