Problem 157 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following mixture can be separated by steam distillation? (a) Benzoic acid and \(\mathrm{NaCl}\) (b) Acetone and methanol (c) Aniline and chlorobenzene (d) O- Nitrophenol and p-nitrophenol

Step-by-Step Solution

Answer

Option (c) Aniline and chlorobenzene can be separated by steam distillation.

Step 1: Understanding Steam Distillation

Steam distillation is a separation process used for temperature-sensitive substances that decompose at their boiling points. It works well for volatile compounds that are immiscible with water.

Step 2: Analyze Each Option

Consider which of the substances in each option is a volatile and water-immiscible compound, making them suitable for steam distillation: (a) Benzoic acid is non-volatile and not suitable. (b) Acetone and methanol are both volatile, but they are miscible, making steam distillation ineffective. (c) Aniline and chlorobenzene are both volatile and sparingly soluble in water. (d) Both o-nitrophenol and p-nitrophenol have similar boiling points and similar solubility properties, making them hard to separate this way.

Step 3: Review Aniline and Chlorobenzene

Aniline and chlorobenzene have significantly different boiling points. Aniline is an aromatic amine, and chlorobenzene is a halogenated aromatic hydrocarbon, both of which are suitable for separation by steam distillation due to being volatile and immiscible in water.

Key Concepts

Volatile Compounds

Volatile compounds are substances that can easily vaporize at relatively low temperatures. This characteristic makes them ideal candidates for processes like steam distillation. Here are some key properties of volatile compounds:

• They possess lower boiling points compared to non-volatile compounds.
• They often have a high vapor pressure at room temperature.
• They are generally easier to separate because they disengage from mixtures when heat is applied.

In steam distillation, the primary goal is to remove these volatile substances from a mixture without the need to apply excessive heat. This is crucial when working with heat-sensitive materials that can decompose if their boiling points are reached.

Temperature-Sensitive Substances

Some compounds are sensitive to heat, meaning they may decompose or have adverse reactions when exposed to high temperatures. Temperature-sensitive substances are suitable for steam distillation because this gentle method prevents degradation:

• The process allows for separation without reaching the high boiling point, minimizing the risk of decomposition.
• Steam lowers the boiling point of the respective components, which is especially helpful for delicate compounds.
• Preserving the structural integrity of these substances is imperative for their effectiveness in their intended applications.

Using steam distillation, temperature-sensitive substances retain their properties, ensuring their usefulness in various industries, such as pharmaceuticals and perfumes.

Boiling Points

The boiling point of a substance is the temperature at which its vapor pressure equals the ambient pressure. When dealing with mixtures, the differences in boiling points become a critical factor in separation techniques like steam distillation:

• Substances with significantly different boiling points are easier to separate through steam distillation.
• Compounds like aniline and chlorobenzene can be efficiently separated because their different boiling points result in one vaporizing while the other remains in liquid form.
• The method allows for separation at boiling points lower than the standard through the interaction with steam.

Steam distillation effectively leverages these properties to isolate specific components without compromising their quality.

Separation Process

Steam distillation is an effective separation process for extracting volatile compounds from mixtures. It leverages the immiscibility of certain compounds in water to facilitate separation:

• By introducing steam, the boiling point of the volatile compounds is reduced via the formation of a temporary azeotrope with water.
• The process is particularly useful for compounds that would be damaged at higher temperatures or are difficult to separate through other means.
• The technique is employed in a variety of industries, from essential oil production to chemical manufacturing.

This method ensures that sensitive volatile compounds can be safely isolated, maintaining their functional properties for subsequent use or analysis.