Question

Impure glycerine is purified by: (a) Vacuum distillation (b) Simple distillation (c) Steam distillation (d) None of the above

Short answer

Glycerine is purified by steam distillation (option c).

Step-by-step solution

Understanding the Process

The question asks which method is used to purify impure glycerine. We need to consider each option and how it affects the purification of a substance like glycerine.

Examining Vacuum Distillation

Vacuum distillation is a technique where the pressure is reduced to lower the boiling point of substances, enabling distillation at lower temperatures. This is especially useful for substances that decompose at higher temperatures.

Examining Simple Distillation

Simple distillation is a method used to separate components based on differences in their boiling points. It is typically used for mixtures with large differences in boiling points.

Examining Steam Distillation

Steam distillation involves using steam to distill temperature-sensitive components that can decompose at higher boiling points. This technique is ideal for separating substances like glycerine that may degrade if heated directly.

Eliminating Incorrect Options

Simple distillation isn't suitable for glycerine as it cannot handle components that decompose under high direct heat. Similarly, the vague term 'None of the above' does not fit since there are applicable methods for purification. Thus, we focus on vacuum and steam distillation.

Choosing the Appropriate Technique

Both vacuum and steam distillation prevent decomposition. However, steam distillation is especially suited for purifying organic compounds like glycerine without risk of thermal decomposition. Thus, the correct answer is steam distillation.

Key concepts

Vacuum Distillation

Vacuum distillation is an efficient technique used to purify compounds that might decompose if distilled at higher temperatures. By reducing the pressure within the distillation apparatus, the boiling point of the substances is effectively lowered. This means that volatile components can be distilled at temperatures that would otherwise be too high and risk thermal decomposition.
This technique is commonly utilized in refining industries and for sensitive organic compounds. It is particularly useful for attracting components with high boiling points, minimizing the likelihood of chemical degradation during the extraction process.

• Reduces boiling point by lowering pressure, suitable for heat-sensitive compounds.
• Commonly used in industrial settings and for high-boiling organic compounds.

Steam Distillation

Steam distillation is a specialized purification process ideal for isolating temperature-sensitive organic compounds. It utilizes steam to distill substances gently and avoids direct heating that could lead to decomposition. When the steam interacts with the mixture, it forms an azeotropic mixture with the organic material, lowering the overall boiling point.
This method is favored in the extraction of essential oils and purification of organic solvents like glycerine.

• Ideal for purifying compounds at temperatures lower than their boiling points.
• Prevents thermal decomposition by using steam instead of direct heating.
• Frequently applied in the essential oil industry and organic solvent purification.

Organic Compound Separation

Separating organic compounds is a pivotal process in chemical purification techniques. The method chosen depends on the nature of the compound and its thermal stability. For instance, compounds with very different boiling points can often be separated using simple or fractional distillation. However, vacuum or steam distillation is preferred when dealing with thermally sensitive substances.
Glycerine, being an organic compound, is best purified using steam distillation due to its sensitivity to heat. This ensures that it remains stable and uncontaminated throughout the purification process.

• Method selection is based on boiling point differences and thermal stability.
• Vacuum and steam distillation are favored for heat-sensitive organic compounds.
• Ensures the stability and purity of compounds like glycerine during separation.