Question

Aniline and water mixture can be separated by (A) Fractional distillation (B) Steam distillation (C) Crystallisation (D) Distillation under reduced pressure

Short answer

The most suitable method for separating a mixture of aniline and water is steam distillation (B). This method efficiently separates the components by utilizing their difference in boiling points and minimizes the risk of thermal decomposition of aniline.

Step-by-step solution

Evaluate the different separation methods

First, we need to determine which of the given separation methods is best suited for our task. The key difference between the methods is the principle by which they separate components of a mixture. (A) Fractional distillation: Fractional distillation is used to separate a mixture of liquids with different boiling points. This method could be used for separating aniline and water, but it may not be the most efficient method due to the risk of thermal decomposition in sensitive compounds. (B) Steam distillation: Steam distillation involves boiling water and passing the steam through a mixture of compounds. The principle is that some compounds will vaporize with the steam and can be separated. This method is particularly useful for separating compounds with higher boiling points than water, such as aniline, because the steam will help to vaporize these compounds at a lower temperature than their normal boiling point. (C) Crystallisation: Crystallisation is a separation technique that relies on differences in the solubility of compounds in a solvent. However, both aniline and water are miscible liquids, so this method would not be suitable for their separation. (D) Distillation under reduced pressure: This technique involves lowering the pressure in the system, which allows the compounds to boil at lower temperatures. This method can be useful for compounds with high boiling points but is not necessary for separating aniline and water since their boiling points are already significantly different.

Choose the best method for separation

Based on the evaluation of the different separation methods, it is clear that the steam distillation (B) is the most suitable method for separating a mixture of aniline and water. This method allows for efficient separation utilizing their difference in boiling points and minimizes the risk of thermal decomposition of aniline as it vaporizes at a lower temperature than its normal boiling point.

Key concepts

Steam Distillation

Steam distillation is a fascinating separation technique specifically beneficial for compounds that are sensitive to heat. In steam distillation, steam is passed through the mixture, facilitating the distillation process at lower temperatures. This characteristic makes it particularly useful for substances with higher boiling points, like aniline.

Here’s why steam distillation is favored:

• **Lower Temperature Requirement**: By introducing steam, compounds volatilize at temperatures below their normal boiling points.
• **Preserves Heat-Sensitive Compounds**: As the process uses boiling water, it prevents decomposition of the substance being distilled.
• **Efficiency**: It is a practical method for isolating aromatic oils, which are not soluble in water but have high boiling points.

Overall, steam distillation is the perfect choice for separating aniline from water, combining efficiency with gentleness.

Aniline Separation

Separating aniline from a mixture involves utilizing its specific properties. Aniline, a primary amine, presents distinct challenges during separation due to its higher boiling point in comparison to many other common liquid mixtures. This is why steam distillation is a preferred technique in this context.

**Why is Aniline Separation Complex?**

• Aniline has a boiling point of approximately 184°C, making direct distillation ineffective without risking decomposition.
• Being miscible with water adds to the complexity, as typical techniques like crystallization are not suitable.
• The presence of amine groups in its structure interacts with moisture, often complicating purification processes involving direct heat.

Through steam distillation, the intricate separation of aniline is simplified, efficiently taking advantage of boiling point manipulation.

Boiling Point Differences

Understanding boiling point differences is key to many separation techniques. In our scenario, recognizing these differences allows us to choose the best method for extracting clean components from a mixture.

**Why Boiling Points Matter**

• **Thermal Stability**: Compounds with high boiling points like aniline can decompose at elevated temperatures. Therefore, adjusting them for separation is crucial.
• **Selectivity**: Different boiling points enable selective separation when a mixture is heated or steamed, as substances evaporate at different rates.
• **Efficiency in Separation**: The disparity in boiling points streamlines the efficiency of processes like steam distillation where co-distillation with water vapor happens.

So, knowing about boiling points helps in predicting how a solution behaves upon heating, guiding us towards the right separation approach.