Which of the following sets of operation will completely separate a mixture of sodium chloride, sand and iodine?

To solve this problem, we must look at the physical properties of each component in the mixture: sodium chloride (salt), sand, and iodine.

1. Analyze the Components

• Iodine ($I_2$): A solid that undergoes sublimation (changes directly from solid to gas when heated).
• Sodium Chloride ($NaCl$): Highly soluble in water.
• Sand ($SiO_2$): Insoluble in water.

2. Explain the Concept

To separate a mixture, we must choose a sequence of operations where each step targets the unique physical property of one component without interfering with the others.

• Sublimation: Since iodine sublimes, heating the mixture will cause the iodine to turn into vapor, leaving behind the salt and sand.
• Addition of Water: Once the iodine is removed, we add water to the remaining mixture. The salt will dissolve, while the sand will remain as a solid.
• Filtration: This process separates the insoluble sand from the salt solution (filtrate).
• Evaporation to Dryness: Finally, heating the salt solution will evaporate the water, leaving the solid sodium chloride behind.

3. Step-by-Step Solution

1. Sublimation: Heat the mixture. Iodine vaporizes and can be collected, leaving salt and sand.
2. Addition of water: Add water to the remaining salt and sand. The salt dissolves to form a solution.
3. Filtration: Pour the mixture through filter paper. The sand stays on the paper (residue), and the salt solution passes through (filtrate).
4. Evaporation to dryness: Heat the salt solution to remove the water, leaving pure sodium chloride crystals.

4. Identify the Answer

Comparing our logical steps to the options provided:

• Option A is incorrect because you cannot filter before removing the iodine.
• Option B is incorrect for the same reason.
• Option C is incorrect because adding water before sublimation would dissolve the salt while the iodine is still present, making the separation messy and inefficient.
• Option D follows the correct logical sequence: Sublimation $\rightarrow$ Addition of water $\rightarrow$ Filtration $\rightarrow$ Evaporation to dryness.

Exam Tip

When dealing with separation of mixtures, always think about the "easiest" component to remove first. If a component sublimes (like Iodine, Ammonium Chloride, or Naphthalene), sublimation should almost always be your first step!