Question

Which of the following compounds has the lowest boiling point?

• A. KCl
• B. CuCl
• C. CuCl\(_2\)
• D. CsCl

Hint:

Higher polarizing power of the cation (small size, high charge) leads to more covalent character and lower boiling points in ionic compounds.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Boiling point depends on the type of bonding and the strength of intermolecular forces. Ionic compounds generally have high boiling points, but covalent character reduces it.

Step 2: Detailed Explanation:
According to Fajans' rule, a smaller cation with a higher charge has a greater polarizing power, leading to more covalent character in the compound and thus a lower boiling point. • KCl: Large K\(^+\) ion, low polarizing power, ionic, high boiling point. • CuCl: Cu\(^+\) is smaller, has polarizing power, some covalent character. • CuCl\(_2\): Cu\(^{2+}\) is smaller and has a higher charge, so it has the greatest polarizing power, giving the highest covalent character and thus the lowest boiling point. • CsCl: Very large Cs\(^+\) ion, low polarizing power, ionic, high boiling point.

Step 3: Final Answer:
CuCl\(_2\) has the lowest boiling point, which corresponds to option (C).