Question

Trichloroethane is a solvent used to remove grease from clothes. How, after use, is the solvent separated from the grease?
A.By chromatography
B.By crystallization
C.By distillation
D.By filtration

Answer 1

To answer this question, you should recall the concept of properties of trichloroethane. Trichloroethane has been used as a spot remover to clean oil and grease stains in industries from fabrics at inspection stations. It has a low boiling point at ${74^{\text{o}}}{\text{C}}$

Complete step by step answer:
Since the boiling point of Trichloroethane is only ${74^{\text{o}}}{\text{C}}$ , the best way to separate the solvent from grease is by distillation.
Chromatography would be too expensive and very cumbersome.
Crystallization is impractical since the solvent has a melting point of $- 33{{^\circ C}}\;$.
Filtration will only remove particulate matter. It will not remove the grease which is in solution.

Hence, the correct answer to this question is option C.

Additional information:
Detergents and soaps are also used as cleansing agents. Detergents generally are derivatives of alkylbenzene sulfonates, that is a family of compounds that are similar to soap but are more soluble in hard water, due to the reason that the polar part of detergents i.e. sulfonate is less likely than the polar part of soap i.e. carboxylate to bind to ions such as calcium and magnesium commonly found in hard water. They are usually available as powders or concentrated solutions. Detergents, like soaps, work because they are amphiphilic which means it is both hydrophilic (polar) and partly hydrophobic (non-polar). This dual nature of detergents facilitates the removal of the mixture of common hydrophobic impurities like oil and grease with water. It is a fact that air is not hydrophilic, which is the reason why different detergents show varying degrees of foaming. Detergent Solutions being a common glycol base derivative are basic, their pH value tends from 9-10.

Note:
The process of distillation refers to the selective boiling and subsequent condensation of a component in a liquid mixture. It has been used as a separation technique in industries to either increase the concentration of a particular component in the mixture or to obtain pure components from the mixture. The process of distillation is based on the principle of difference in the boiling points of the components in the liquid mixture and acts by forcing one of them into a gaseous state.