What technique is suitable for separating a binary solution of potassium chloride and potassium trioxochlorate (V)?

Analysis

The question asks for the most effective method to separate a mixture of two salts: potassium chloride (KCl) and potassium trioxochlorate(V) (KClO₃). Both are solids that dissolve in water to form a binary solution.

Concept Explanation

To separate two dissolved salts from a solution, we rely on the principle of solubility. Different substances have different solubilities at different temperatures.

• Fractional crystallization is a technique used to separate two or more solutes from a solution based on their different solubilities at varying temperatures.
• As a hot, saturated solution of the mixture cools, the substance with the lower solubility at lower temperatures will crystallize out of the solution first, while the more soluble substance remains dissolved.

Step-by-Step Solution

1. Understand the components: We have a mixture of KCl and KClO₃. Both are soluble in water.
2. Evaluate the methods: • Fractional distillation: Used for separating liquids with different boiling points (e.g., ethanol and water). Not suitable for salts. • Filtration: Used to separate an insoluble solid from a liquid. Since both salts are dissolved, filtration will not separate them. • Evaporation: If you evaporate the water completely, you will get a mixture of both salts as a solid residue, not separated. • Fractional crystallization: Because KClO₃ and KCl have significantly different solubility curves (KClO₃ is much less soluble in cold water than KCl), cooling the hot saturated solution causes the KClO₃ to crystallize out first, effectively separating it from the KCl.
3. Conclusion: Fractional crystallization is the standard laboratory technique for separating mixtures of salts with different temperature-dependent solubilities.

Correct Answer

The correct option is A.

Exam Tip

Whenever you see a question about separating two dissolved salts, immediately think of solubility. If the question mentions "fractional," it is almost always referring to separating components based on a specific physical property (like solubility for crystallization or boiling point for distillation). Don't let the complex chemical names intimidate you—focus on the physical properties!