Question

This section contains multiple choice questions. Each question has 4 choices (a), (b), (c) and (d), out of which ONLY ONE is correct. A mixture of aniline and paranitrobenzoic acid can be separated by using (a) only con. HCl (b) only \(\mathrm{NaHCO}_{3}\) solution (c) only con.HNO \(_{3}\) (d) either conc.HCl or \(\mathrm{NaHCO}_{3}\)

Short answer

Answer: Either con. HCl or \(\mathrm{NaHCO}_{3}\) solution

Step-by-step solution

Reactivity of aniline and para-nitrobenzoic acid with con. HCl

Aniline is a weak base and would react with con. HCl (a strong acid) to form an aniline hydrochloride salt, while para-nitrobenzoic acid would not react with con. HCl, as both are acids. Thus, the two compounds could be separated based on their solubility differences: aniline hydrochloride salt would be soluble in water, while para-nitrobenzoic acid would remain insoluble.

Reactivity of aniline and para-nitrobenzoic acid with \(\mathrm{NaHCO}_{3}\) solution

Para-nitrobenzoic acid, being an acid, would react with \(\mathrm{NaHCO}_{3}\) (a weak base) to form water, carbon dioxide gas, and a sodium salt, which would be soluble in water. Aniline would not react with \(\mathrm{NaHCO}_{3}\) because it is a weak base. This option also allows for the separation of the two compounds based on their solubility differences in water.

Reactivity of aniline and para-nitrobenzoic acid with con. HNO\(_{3}\)

Both aniline and para-nitrobenzoic acid might undergo reactions with con. HNO\(_{3}\). Aniline could be nitrated under these conditions to form nitroaniline derivatives, while para-nitrobenzoic acid could potentially undergo further nitration reactions as well. Since both compounds can react with con. HNO\(_{3}\), using this reagent would not provide an effective way to separate the mixture of these two compounds. Based on the reactivity analysis of the given reagents, the correct choice is: (d) either con. HCl or \(\mathrm{NaHCO}_{3}\) solution

Key concepts

Aniline and Paranitrobenzoic Acid Separation

Separating a mixture of aniline and paranitrobenzoic acid is a key exercise in understanding the practical application of solubility and reactivity principles in organic chemistry. The process exploits the basic nature of aniline and the acidic characteristics of paranitrobenzoic acid.

When introduced to concentrated hydrochloric acid (conc. HCl), aniline, being a weak base, readily forms aniline hydrochloride—a water-soluble salt. In contrast, paranitrobenzoic acid, itself an acid, does not react with conc. HCl and remains insoluble in the aqueous solution. The result is a chemical partitioning based on solubility differences—solid paranitrobenzoic acid can then be filtered off, while aniline hydrochloride remains dissolved.

Another approach involves using a solution of sodium bicarbonate (\(\textrm{NaHCO}_3\)). The biological substance, paranitrobenzoic acid reacts with the weak base to form a soluble sodium salt, leaving aniline unreactive due to its weakly basic nature. This allows for the physical separation where aniline can be filtered from the aqueous solution containing the sodium salt of paranitrobenzoic acid.

Solubility Differences in Organic Chemistry

The solubility differences in organic compounds, such as aniline and paranitrobenzoic acid, play a pivotal role in separation techniques. Organic chemists must often rely on a compound's behavior in the presence of different solvents to purify or isolate specific components of a mixture.

In the separation process, compounds that form ionic salts in reaction with additional reagents become soluble in polar solvents like water, whereas neutral compounds typically retain their original solubility properties—often remaining less soluble in water and more soluble in organic solvents.

Understanding these properties assists in developing a tailored strategy for separating mixtures. For instance, by choosing the right reactant, such as conc. HCl or \(\textrm{NaHCO}_3\), chemists can target specific functional groups within molecules, leading to predictable solubility changes that facilitate separation.

Acid-Base Reactions in Organic Chemistry

Acid-base reactions are a fundamental class of reactions in organic chemistry where proton transfer occurs between an acid and a base. The outcome of such reactions is often the formation or breaking of bonds, with resultant changes in solubility and reactivity of the compounds involved.

Considering our context, paranitrobenzoic acid (an acid) and aniline (a weak base) will behave differently in the presence of other acidic or basic reagents. For instance, aniline forms a salt when treated with conc. HCl, which illustrates its basic nature through the acceptance of a proton (H+ ion). On the other hand, paranitrobenzoic acid reacts with \(\textrm{NaHCO}_3\), a weak base, emphasizing the acid's capability to donate a proton.

These reactions are not only theoretical but have practical applications, allowing for selective separation based on the resulting solubility of the reaction products. Mastering the prediction and outcomes of such acid-base reactions is essential for students to navigate through the complexities of organic synthesis and purification techniques.