Question

This section contains 2 paragraphs. Based upon the paragraph, 3 multiple choice questions have to be answered. Each question has 4 choices \((a),(b),(c)\) and \((d)\), out of which ONLY ONE is correct. In order to identify and characterize the various functional groups present in an organic compound (or a mixture of organic compounds), a complete knowledge of the tests answered by these functional groups is essential. An organic compound burns with a sooty flame and gives a violet colouration with neutral \(\mathrm{FeCl}_{3}\) solution. It gives effervescence when treated with metallic sodium and also with sodium bicarbonate solution. The compound could be (a) phenol (b) benzoic acid (c) salicyclic acid (d) toluic acid

Short answer

Answer: Salicylic acid.

Step-by-step solution

Analyze the information given in the text

The given information about the organic compound is as follows: 1. Burns with a sooty flame. 2. Gives violet coloration with neutral FeCl3 solution. 3. Gives effervescence when treated with metallic sodium. 4. Gives effervescence when treated with sodium bicarbonate.

Compare characteristics of given choices

Next, we compare the given characteristics with the known properties of the given choices: (a) Phenol: Phenols show a reaction with FeCl3 (forming a violet coloration), but they do not react with sodium bicarbonate. (b) Benzoic acid: Benzoic acid reacts with both neutral FeCl3 (forming a violet coloration) and sodium bicarbonate, but burns with a non-sooty flame. (c) Salicylic acid: Salicylic acid reacts with neutral FeCl3 (forming a violet coloration) and sodium bicarbonate, and also burns with a sooty flame due to the presence of an aromatic ring with both the hydroxyl and carboxyl groups. (d) Toluic acid: Toluic acid reacts with neutral FeCl3, but not with sodium bicarbonate.

Identify the correct option

Based on the given information and characteristics of the options provided, the correct answer is: (c) Salicylic acid, since it matches all given characteristics of the organic compound.

Key concepts

Organic compound characterization

Characterizing organic compounds is a crucial aspect of organic chemistry that allows chemists to determine the structure and composition of molecules. This process involves a series of tests that reveal the presence and nature of different functional groups within the compound.

For students tackling this concept, it's important to recognize visual clues, such as a sooty flame indicating a carbon-rich compound, possibly with an aromatic ring. Observing reactions with certain reagents can also pinpoint specific groups. For instance, the reaction with neutral FeCl3 that gives a violet coloration is a hallmark of phenols and their derivatives. Similarly, the effervescence with sodium and sodium bicarbonate is indicative of the presence of acidic hydrogen atoms, as these substances react with acids to produce carbon dioxide gas.

To fully grasp organic compound characterization, students should practice identifying the key tests for common functional groups and predicting the outcomes based on the structure of an organic molecule.

FeCl3 test in organic chemistry

The FeCl3 test is routinely used in the qualitative analysis of phenols and enols. When an organic compound reacts with neutral FeCl3 solution and produces a violet coloration, it suggests the presence of a phenolic group. This is due to the formation of a complex between the iron(III) ions and the phenol, resulting in the characteristic color.

The FeCl3 test is specific and sensitive, making it a reliable method for identifying phenolic compounds in a mixture. Students should note, however, that not all compounds that react with FeCl3 are phenols; other groups, like enols and certain carboxylic acids, can also elicit a positive result. Understanding the structural features that give rise to this reaction is fundamental to interpreting the test accurately.

Sodium bicarbonate test in organic chemistry

In the realm of functional group tests, the sodium bicarbonate test is a simple yet informative reaction. It's commonly used to test for the presence of carboxylic acids. During this test, a compound that reacts with sodium bicarbonate to release carbon dioxide gas is likely to be an acid, since the reaction is a typical acid-base reaction.

Effervescence, or the rapid release of gas bubbles, indicates a positive test result, confirming the presence of an acidic functional group, such as the carboxyl group in carboxylic acids. This test helps distinguish carboxylic acids from other acidic groups like phenols, which are weak acids and do not react with sodium bicarbonate. Students should comprehend that the absence of effervescence with sodium bicarbonate does not rule out the presence of an acidic hydrogen, but it does help narrow down possible functional groups.