Question

Which of these solutions has the highest freezing point?

Answer 1

Answer: Option (a) is the correct answer.

Explanation:

Depression in freezing point depends on Vant Hoff factor. So, more is the number of dissociated ions lesser will be the freezing point.

Mathematically,      $\Delta T_{f} = iK_{f}m$

where   $\Delta T_{f}$ = freezing point depression

                             i = Vant Hoff factor

               $K_{f}$ = freezing point depression

                           m = molality of the solution      

The ratio between concentration of particles that are actually produced when a substance is dissolved and the concentration of a substance calculated from its mass is known as Vant Hoff factor.

Mathematically,    i = $\frac{\text{total no. of moles of particles after association/dissociation}}{\text{No. of moles of particles before association/dissociation}}$

For dissociation i is greater than or equal to 1.  1 then dissociation has taken place. When i = 1 then neither association or dissociation has taken place.  

Hence, sucrose will have i = 1 as it produces only one ion.

Sodium chloride will have i = 2 as it produces two ions.

Calcium bromide will have i = 3 as it produces three ions.

Aluminium bromide will have i = 4 as it produces four ions.

Potassium chloride will have i = 2 as it produces two ions.

Therefore, we can conclude that sucrose solution will have highest freezing point.

Answer 2

Colligative properties depend on the amount of solute dissolved in a solvent. These set of properties do not depend on the type of species present. These properties include freezing point depression, boiling point elevation, osmotic pressure and vapor pressure lowering. The one that would have the highest freezing point would be the sucrose (FIRST OPTION) since its vant hoff factor is 1. Hope this answers the question.