Question

A mixture of benzene and chloroform is separated by: (a) Sublimation (b) Separation funnel (c) Crystallization (d) Distillation

Short answer

Distillation is used to separate a benzene and chloroform mixture.

Step-by-step solution

Understanding the Mixture

A benzene and chloroform mixture is a combination of two liquids. Given their properties, such as boiling points, we must consider separation methods that are effective for liquid-liquid mixtures.

Considering Separation Methods

Each option must be evaluated: - Sublimation involves a solid changing directly to a gas and is not applicable to liquid mixtures. - A separation funnel is used for immiscible liquids, but benzene and chloroform are miscible. - Crystallization is for solid-liquid separations. - Distillation separates liquids based on different boiling points.

Identifying Distillation

Distillation is used to separate benzene and chloroform because they have different boiling points, allowing them to be separated through heating and condensation. Benzene boils at 80.1°C and chloroform at 61.2°C. Distillation uses this boiling point difference to separate the two liquids effectively.

Decision

After considering the properties of benzene and chloroform and each separation method, distillation is the suitable technique for separating this mixture, due to the different boiling points of the substances.

Key concepts

Liquid-Liquid Separation

Liquid-liquid separation is an essential process in chemistry and industry where two mixed liquids need to be separated from each other. This separation is performed based on the physical properties of the liquids, such as their density, solubility, or boiling points. There are several methods to achieve this separation, each suited to different types of liquid mixtures.

One common approach to separate liquids is using a separation funnel. This technique is effective for immiscible liquids, which do not mix at all or only minimally. Immiscible liquids form layers based on their density and can be easily separated by draining the bottom layer from the funnel. However, when dealing with miscible liquids like benzene and chloroform, other methods must be employed.

In cases where liquids are miscible, and traditional separation funnels can't be used, distillation becomes a preferred method. Distillation leverages the unique boiling points of the liquids, allowing one liquid to be evaporated and then condensed back into a separate container, effectively isolating it from the rest of the mixture.

Boiling Points

Boiling points are a critical concept in the process of distillation. Each liquid has a specific temperature at which it changes from a liquid to a gas, known as the boiling point. This property is utilized in distillation to separate liquids with different boiling points.

For instance, benzene and chloroform are two common miscible liquids. Benzene has a boiling point of 80.1°C, while chloroform boils at a lower temperature of 61.2°C. During distillation, heat is applied to the mixture. The liquid with the lower boiling point, chloroform, will evaporate first. This vapor is then cooled and collected as a separate liquid in another container, effectively separating it from benzene.

Understanding boiling points not only helps in separation processes but is also crucial for determining the conditions under which a mixture can be separated. It's important to note that boiling points can sometimes be affected by pressure, such as at high altitudes, where liquids boil at lower temperatures.

Miscible Liquids

Miscible liquids are those that can mix together in any proportion without forming separate layers. Unlike immiscible liquids, which remain distinct when combined, miscible liquids mix uniformly at the molecular level.

An example of miscible liquids is the mixture of benzene and chloroform. Both these liquids can dissolve into each other completely, forming a single-phase mixture. However, when separation of these liquids is necessary, methods that exploit differences in their physical properties, such as distillation, are used.

Being aware of the miscibility of liquids is crucial when choosing a separation technique. For miscible liquids, factors like their boiling points or even their chemical interactions with other substances may be considered. This is because they can't be separated by simple mechanical means, such as using a separation funnel, which is reserved for immiscible mixtures.