Absolute alcohol cannot be prepared by fractional distillation of rectified spirit since:

Options

A. It forms azeotropic mixture
B. It is used as power alcohol
C. It is used in wines
D. None of the above

Answer

To solve the question of why absolute alcohol cannot be prepared by fractional distillation of rectified spirit, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Rectified Spirit**:
- Rectified spirit typically contains about 95.57% ethanol and 4.43% water. This mixture is not pure ethanol.

**Hint**: Remember the composition of rectified spirit is crucial in understanding its behavior during distillation.

2. **Concept of Azeotropic Mixtures**:
- An azeotropic mixture is a mixture of two or more liquids that has a constant boiling point and composition throughout the distillation process. In the case of rectified spirit, the ethanol and water form an azeotropic mixture.

**Hint**: Azeotropes behave differently than ideal mixtures; they do not separate completely upon boiling.

3. **Boiling Point of the Azeotropic Mixture**:
- The azeotropic mixture of ethanol and water has a boiling point of approximately 78.2°C. This boiling point is lower than that of pure water and higher than that of pure ethanol.

**Hint**: The boiling point of the azeotropic mixture is key to understanding why distillation won't yield pure ethanol.

4. **Distillation Process**:
- During fractional distillation, both ethanol and water will vaporize together at this boiling point, maintaining the same ratio of components (95.57% ethanol and 4.43% water) in the vapor phase.

**Hint**: Consider how the vapor composition relates to the liquid composition during distillation.

5. **Conclusion**:
- Because the components of the azeotropic mixture distill together in a fixed proportion, it is impossible to obtain absolute (pure) ethanol from rectified spirit through fractional distillation.

**Hint**: Reflect on the implications of fixed proportions in distillation when dealing with azeotropes.

### Final Answer:
Absolute alcohol cannot be prepared by fractional distillation of rectified spirit because it forms an azeotropic mixture, which distills at a constant boiling point, preventing the separation of ethanol from water.