Question

Mixture of anthracene and benzoic acid can be separated by (A) Fractional distillation (B) Sublimation (C) Chromatography (D) Filtration

Short answer

The most suitable method to separate a mixture of anthracene and benzoic acid is sublimation (Option B), as anthracene sublimates while benzoic acid does not. Other methods like fractional distillation, chromatography, and filtration are not suitable due to the properties of the compounds and the nature of the mixture.

Step-by-step solution

Understanding the properties of anthracene and benzoic acid

Anthracene is a solid aromatic hydrocarbon that consists of three fused benzene rings. It is insoluble in water, sublimates, and has a relatively low melting point. Benzoic acid, on the other hand, is an organic compound that is also a solid at room temperature. It is slightly soluble in water and has a higher melting point compared to anthracene.

Evaluating each separation technique

(A) Fractional distillation: This technique is used to separate liquids with different boiling points. Since both anthracene and benzoic acid are solids, this method is not suitable. (B) Sublimation: Sublimation is the process where a solid is converted directly into a gas without passing through the liquid phase. As mentioned earlier, anthracene sublimates while benzoic acid does not. Therefore, sublimation can be used for separating the mixture. (C) Chromatography: Chromatography separates components based on their affinities for a stationary phase and mobile phase. While chromatography might work, it is a more complex and time-consuming method compared to sublimation. (D) Filtration: Filtration is used for separating solids from liquids or insoluble solids from other solids. In this case, both anthracene and benzoic acid are solids, and filtration cannot be used to separate them.

Choosing the best method for separation

Based on the evaluation of the four separation techniques, we can conclude that the most suitable method to separate a mixture of anthracene and benzoic acid is sublimation (Option B).

Key concepts

Sublimation

Sublimation is a fascinating separation technique where a solid turns directly into a gas without going through the liquid stage. This might seem a bit magical, but it's all about the right conditions!

• Specific Solids: Not every solid can sublimate. This process is ideal for substances that can easily transition from solid to gas. Anthracene is one such solid.
• Pressure and Temperature: Sublimation generally occurs under specific temperature and pressure conditions. Usually, it's done at atmospheric pressure but can be manipulated via heat.

In the context of the exercise, anthracene's ability to sublimate distinguishes it from benzoic acid, which doesn't easily sublimate. By heating the mixture, only the anthracene will turn into vapor, leaving benzoic acid behind. This makes it an efficient and straightforward method to separate these two components.

Chromatography

Chromatography is a versatile and sophisticated separation technique used to analyze and purify various substances. It is based on the principle of different affinities of compounds to stationary and mobile phases.

• Stationary and Mobile Phases: During chromatography, a mixture is passed through a stationary phase, while a mobile phase carries the compounds. Different compounds travel at varying speeds due to interaction differences with these phases.
• Types of Chromatography: There are several types of chromatography including paper, thin-layer, and gas chromatography, each suited for specific separation needs.

Though effective, chromatography is often more complex and time-consuming compared to other methods like sublimation. In the given exercise, while chromatography could potentially separate anthracene and benzoic acid, it may not be the most efficient choice in terms of simplicity and speed.

Organic Compounds Separation

Separating organic compounds can be quite tricky due to the similarities many of them share, such as melting or boiling points. A thorough understanding of the compounds’ properties is essential.

• Analytical Techniques: Knowledge of techniques such as distillation, filtration, chromatography, and sublimation is crucial for effective separation. Each method has its own purpose and is suited to separating specific types of mixtures.
• Choosing the Right Method: The selection of a separation technique hugely depends on the physical and chemical properties of the substances. Methods like sublimation exploit unique properties such as the ability of a compound to transition to the vapor phase easily.

In the case of anthracene and benzoic acid, their distinct responses to heat make sublimation the optimal choice for separation. Understanding such properties ensures a more efficient and less resource-intensive separation process.