Problem 81 - A Complete Resource Book in Chemistry for JEE Main

Question

Identify the wrong statement from the following: (a) methyl salicylate is an ester (b) salicylic acid is a monobasic acid (c) methyl salicylate does not occur in natural oils (d) salicylic acid gives violet colour with neutral ferric chloride as well as brisk effervescence with sodium bicarbonate.

Step-by-Step Solution

Answer

Statement (c) is wrong; methyl salicylate occurs in natural oils.

Step 1: Understanding Esters

Recognize that methyl salicylate is a chemical compound and is known to be an ester. Esters are typically characterized by their pleasant smells and are derived from the reaction of an acid with an alcohol, eliminating water. Hence, statement (a) "methyl salicylate is an ester" is correct.

Step 2: Identifying a Monobasic Acid

Salicylic acid has only one ionizable hydrogen atom, meaning it can donate only one proton (H+) in an aqueous solution, which classifies it as a monobasic acid. Therefore, statement (b) "salicylic acid is a monobasic acid" is correct.

Step 3: Natural Occurrence of Methyl Salicylate

Methyl salicylate is well-known to occur naturally, especially in certain plant essential oils like wintergreen oil. Because it is indeed found in natural oils, statement (c) "methyl salicylate does not occur in natural oils" is wrong.

Step 4: Reactions of Salicylic Acid

Salicylic acid, when treated with neutral ferric chloride, gives a violet color, indicating the presence of phenolic OH groups. Additionally, when reacted with sodium bicarbonate, it results in brisk effervescence due to the release of carbon dioxide. Hence, statement (d) "salicylic acid gives violet colour with neutral ferric chloride as well as brisk effervescence with sodium bicarbonate" is correct.

Key Concepts

Esters

Esters are a fascinating class of organic compounds that play a crucial role in everyday life, from fragrances to pharmaceuticals. They are commonly known for their pleasant aromas, which is why they are often used in perfumes and flavorings. An ester is formed through a reaction known as esterification, where an acid reacts with an alcohol in the presence of a catalyst to produce the ester and water.
The general formula for an ester is RCOOR', where R and R' are hydrocarbon chains.

• The part of the molecule derived from the acid is called the acyl group.
• The part from the alcohol is the alkyl group.

Methyl salicylate, for instance, is an ester formed from salicylic acid and methanol. This compound is commonly found in wintergreen oil and exhibits a characteristic minty aroma.

Monobasic Acids

Monobasic acids are acids that contain only one ionizable hydrogen atom in their structure. This means they can donate only one proton (H⁺) per molecule when dissolved in water, leading to the term "monobasic."
An essential aspect of understanding acids is knowing their ionization potential. In the case of monobasic acids, this potential is simpler compared to acids with multiple ionizable hydrogens.

• Hydrochloric acid (HCl) is a classic example alongside organic acids.
• Monobasic acids react with bases to form salts and water, similar to other acids.

Salicylic acid is a well-known monobasic acid in organic chemistry because it has only one ionizable hydrogen atom.
This makes it able to participate in reactions typical for monobasic acids, such as donating a proton to form salts.

Salicylic Acid Reactions

Salicylic acid is widely recognized for its involvement in various chemical reactions, especially in the field of organic chemistry. It possesses a phenolic hydroxyl group and a carboxylic acid group, making it reactive in different scenarios.
One famous reaction is the test with neutral ferric chloride, where salicylic acid produces a violet complex.

• This reaction is a common qualitative test for phenolic compounds due to the presence of the hydroxyl group.

Moreover, salicylic acid reacts with bases such as sodium bicarbonate to release carbon dioxide, leading to brisk effervescence.
This is because the acid-base reaction results in the formation of sodium salicylate and carbonic acid, which quickly decomposes to release CO₂ gas.

• These reactions help identify functional groups and validate the presence of salicylic acid in mixtures.

These chemical properties underscore the importance of salicylic acid in both analytical chemistry and practical applications.