Question

Match the following aqueous solutions with the appropriate letter from the column on the right. 1.0.12 m CoCl2 2.0.13 m CuBr2 3.0.14 m Crci 4.0.46 m Ethylene glycol(nonelectrolyte) A. Lowest freezing point B. Second lowest freezing point C. Third lowest freezing point D. Highest freezing point Submit Answer Retry Entire Group 3 more group attempts remaining

Answer 1

1. 0.12m CoCl₂                                                D. Highest freezing point.

2. 0.13m CuBr₂                                                C. Third lowest freezing point.

3. 0.14m CuCl₂                B. Second lowest freezing point.

4. 0.46m Ethylene glycol (a nonelectrolyte)    A. Lowest freezing point.

We know for freezing point depression we have $\Delta$ Tf = Tf(pure solvent) - Tf(solution) = i X Kf X m

where $\Delta$ Tf is the depression of freezing point, Tf(pure solvent) is the melting point of pure solvent, Tf(solution) is the melting point of the solution, i is Van't Hoff factor(applicable for electrolytes), Kf is freezing point depression constant & m stands for molality.

Here Kf is constant which is 1.86 0C/m because the solvent is water. So, Tf depends upon i and m only. i is 1 for nonelectrolyte and for most of the electrolytes(ionic compounds) it is actually the number of discrete ions that exist in the formula unit, m is given for each of the solutions.

Thus after calculations, we find the values of Tf for each of the solutions are 0.6696 0C, 0.7254 0C, 0.7812 0C, 0.8556 0C respectively.

Thus from the values obtained we can conclude the amount of freezing point depression.

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