Question

Choose the incorrect statement from the following.

• A. Acetic acid on reaction with HI and red P at 473 K gives iodoethane.
• B. Acetic acid is a weaker acid than formic acid.
• C. Acetic acid gives effervescence with aqueous NaHCO3 solution.
• D. Acetic acid does not reduce Fehling's solution.

Hint:

Acetic acid reacts with HI to give iodoacetic acid, not iodoethane. Always consider the functional group and its reactivity before concluding the product.

Answer 1

The Correct Option is A

Step 1: Understand the reaction of acetic acid with HI and red phosphorus.
Acetic acid (\( \text{CH}_3\text{COOH} \)) reacts with HI (hydriodic acid) and red phosphorus to give iodoethane (\( \text{CH}_3\text{CH}_2\text{I} \)). This reaction is incorrect because, in this case, the carboxyl group (\( \text{COOH} \)) would be replaced by iodine, which typically leads to the formation of iodine derivatives of carboxylic acids. In fact, the correct reaction would produce acetic acid derivatives like iodoacetic acid, not iodoethane. Thus, statement (A) is incorrect.

Step 2: Analyze statement (B).
Acetic acid is indeed a weaker acid than formic acid. This is because formic acid has a stronger acidic character due to the electron-withdrawing -OH group attached to the carbonyl group, making it easier to release the proton. So, statement (B) is correct.

Step 3: Analyze statement (C).
Acetic acid reacts with sodium bicarbonate (\( \text{NaHCO}_3 \)) to produce effervescence due to the evolution of \( \text{CO}_2 \). This is a typical reaction of carboxylic acids with bases. So, statement (C) is correct.

Step 4: Analyze statement (D).
Acetic acid does not reduce Fehling’s solution, which is used to detect aldehydes. Since acetic acid is a carboxylic acid and does not contain an aldehyde group, it cannot reduce Fehling's solution. Therefore, statement (D) is correct.

Step 5: Conclusion.
Thus, the incorrect statement is (A), and the correct answer is option (A).