Question

Match the type of mixture of compounds in Column-I with the technique of separation/purification given in Column-II. Column-I Column-II (A) Two solids which have different solubilities in (P) Steam distillation a solvent and which do not undergo reaction when dissolved in it. (B) Liquid that decomposes at its boiling point (C) Steam volatile liquid (Q) Fractional distillation (D) Twoliquids which have boiling points close (R) Simple distillation to each other. (S) Distillation under reduced pressure (E) Two liquids with large difference in boiling points (T) Crystallisation

Short answer

The correct matchings for each mixture type in Column-I with the separation/purification technique in Column-II are as follows: - (A) matches with (T) - (B) matches with (S) - (C) matches with (P) - (D) matches with (Q) - (E) matches with (R)

Step-by-step solution

Match (A)

In the case of two solids which have different solubilities in a solvent and do not undergo any reaction, the appropriate technique to separate them would be the process of crystallization. The correct match is (A)-(T).

Match (B)

For a liquid that decomposes at its boiling point, we need a technique that prevents the substance from decomposing while still purifying it. In this case, the suitable separation technique is distillation under reduced pressure. Therefore, the correct match is (B)-(S).

Match (C)

A steam volatile liquid can typically be separated through steam distillation. In this process, steam is passed through the mixture to retrieve the volatile components. The correct match for (C) is (P).

Match (D)

Two liquids that have boiling points close to each other can be quite difficult to separate; however, fractional distillation is the technique best suited for this. Fractional distillation involves separating components with similar boiling points via the use of a fractionating column. Therefore, the proper match for (D) is (Q).

Match (E)

Two liquids with a large difference in boiling points can be separated simply and efficiently through the process called simple distillation. The liquid with the lower boiling point will evaporate first and then condense, successfully separating it from the other component. Hence, the correct match for (E) is (R). To summarize the pairings: - (A) matches with (T) - (B) matches with (S) - (C) matches with (P) - (D) matches with (Q) - (E) matches with (R)

Key concepts

Crystallisation

Understanding crystallisation is crucial for students tackling separation techniques in their organic chemistry courses. It's a process where a solid forms from a solution, substance, or melt, yielding crystal structures. Each crystal comprises a pure compound. An everyday example is the formation of salt crystals from evaporated seawater. In the laboratory, this technique is particularly useful for purifying solids that have different solubilities in a solvent. When the solution is allowed to cool, the compound with the higher solubility product forms crystals first, leaving the less soluble impurities in the solution.

• It is important to control the cooling rate to ensure that perfectly formed crystals are achieved.
• The choice of solvent is also key, as it should dissolve the compound when hot but not when cold.

Students should understand that filtration can separate the pure crystals from the remaining solution, obtaining a substance that's notably purer than the original mixture.

Distillation Under Reduced Pressure

The technique of distillation under reduced pressure, also known as vacuum distillation, is vital when a liquid's boiling point is high or it decomposes upon heating to its boiling temperature. Under reduced pressure, the boiling point decreases; hence, the substance can be purified without degradation. This process is not only applicable in labs but is widely used in industries to separate compounds with high boiling points.

• Vacuum pumps commonly achieve the pressure reduction, allowing for the distillation process at substantially lower temperatures.
• This technique is beneficial for temperature-sensitive compounds that might otherwise decompose.

Steam Distillation

In the case of steam distillation, the primary focus is on the separation of compounds that are steam volatile and immiscible with water. This method takes advantage of the lower boiling point of the mixture of the target compound and water, relative to that of the pure components. Steam distillation is often used for purifying and isolating fragrances, essential oils, and other compounds that would degrade at their boiling points.

• One of the process's key benefits is its ability to purify heat-sensitive materials without decomposition.
• Another advantage is its capacity to separate compounds with very high boiling points at much lower temperatures when mixed with steam.

Fractional Distillation

Fractional distillation is a more advanced version of distillation designed to separate a mixture into its individual components. This technique is specifically used when the boiling points of two substances are close to each other and cannot be separated by simple distillation. Components separate based on the efficiency of the fractionating column, where repeated vaporization-condensation cycles occur, leading to an increase in the purity of substances.

• Students should understand the significance of the fractionating column's packing, which increases the surface area for repeated vaporization-condensation cycles.
• The more efficient the column, the more effectively it will separate components with similar boiling points.

Simple Distillation

When discussing simple distillation, we are referring to the most fundamental form of distillation. It's suitable for separating a volatile liquid from a non-volatile component or liquids that have a large difference in their boiling points. During this process, the liquid with a lower boiling point vaporizes first, while the vapors are then condensed back into a liquid and collected apart from the original mixture.

• This method is easy to execute and understand, making it a perfect starting point for students learning about separation techniques.
• Simple distillation is less efficient when separating liquids with close boiling points; however, it serves as a foundation for understanding more complex distillation methods.