How will you purify a sample of benzoic acid containing sodium chloride as impurity ?

Answer

To purify a sample of benzoic acid containing sodium chloride as an impurity, you can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Properties**:
- Recognize that benzoic acid is a solid that can sublime, meaning it can transition from a solid to a gas without becoming a liquid when heated.
- Sodium chloride (table salt) does not sublime and remains solid at the heating temperatures used for benzoic acid.

2. **Heating the Mixture**:
- Heat the mixture of benzoic acid and sodium chloride in a controlled manner. The temperature should be between 320 K to 370 K (approximately 47 °C to 97 °C). This temperature range is sufficient to convert benzoic acid into its gaseous form while leaving sodium chloride solid.

3. **Sublimation Process**:
- As the mixture is heated, benzoic acid will sublime and turn into vapor. The sodium chloride will remain in the solid state and will not evaporate.

4. **Condensation**:
- Set up a cooling system (like a condenser) above the heated mixture to capture the vaporized benzoic acid. As the vapor rises and comes into contact with the cooler surface, it will condense back into solid benzoic acid.

5. **Collection of Purified Benzoic Acid**:
- Collect the solid benzoic acid that has condensed. This solid will be free from sodium chloride, effectively purifying the benzoic acid.

6. **Final Check**:
- Optionally, you can check the purity of the benzoic acid using techniques such as melting point determination or spectroscopy.

### Summary:
The purification of benzoic acid from sodium chloride is effectively achieved through the sublimation process, where benzoic acid is heated, sublimed, condensed, and collected, leaving the sodium chloride behind.

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