JEE Chemistry Aldehydes Ketones And Carboxylic Acids MCQs Set 16

Answer: (b) Koch reaction

Explanation:
1. Carbonylation of an alkene with CO and water under acid catalysis to give a carboxylic acid is the Koch reaction.

Teacher's Note:
1. Count carbons before and after the reaction to avoid mistakes in chain-length changes.
2. Check whether the reagent is a reducing, oxidising or dehydrating agent before choosing the product.

Answer: (a) naphthalene

Explanation:
1. Naphthalene with V₂O₅ and air at about 350°C gives phthalic anhydride.

Teacher's Note:
1. Eliminate options by checking functional groups on both sides of the reaction.
2. Only one option will have the correct functional group and carbon skeleton.

Answer: (b) benzoic acid

Explanation:
1. The Grignard reagent adds to CO₂ to give C₆H₅COOMgBr.
2. Hydrolysis gives benzoic acid.

Teacher's Note:
1. Revise the physical properties such as hydrogen bonding and boiling points together with the chemistry.
2. Compare similar compounds in pairs when you are asked to rank them.

Answer: (b) crystallising, separating and melting acetic acid

Explanation:
1. Pure acetic acid freezes at 16.6°C into ice-like crystals.
2. Cooling, separating and melting them gives glacial acetic acid.

Teacher's Note:
1. Learn the reactivity order of acid derivatives: acyl chloride, anhydride, ester, amide.
2. Most questions of this type are solved by recalling the standard reagent and product pair.

Answer: (a) the acid

Explanation:
1. Isotope-labelling shows that acyl-oxygen cleavage occurs: the acid loses its OH and the alcohol loses only H.

Teacher's Note:
1. Always link acid strength to the stability of the carboxylate ion.
2. Electron-withdrawing groups increase acidity and electron-donating groups decrease it.

Answer: (c) esterification

Explanation:
1. The product is ethyl acetate and the reaction of an acid with an alcohol to form an ester is esterification.

Teacher's Note:
1. Note the name reaction and write its equation once in your notebook.
2. Such one-step recall questions are common in the JEE and NEET style papers.

Answer: (d) H₂NCONH₂

Explanation:
1. NH₄Cl + KCNO → NH₄CNO + KCl, and ammonium cyanate rearranges to urea (Wohler's synthesis).

Teacher's Note:
1. Count carbons before and after the reaction to avoid mistakes in chain-length changes.
2. Check whether the reagent is a reducing, oxidising or dehydrating agent before choosing the product.

Answer: (c) Beckmann rearrangement

Explanation:
1. The acid-catalysed conversion of an oxime into an N-substituted amide is the Beckmann rearrangement.

Teacher's Note:
1. Eliminate options by checking functional groups on both sides of the reaction.
2. Only one option will have the correct functional group and carbon skeleton.

Answer: (b) dry HCl + C₂H₅OH

Explanation:
1. Fischer esterification needs an acid catalyst such as dry HCl with the alcohol.
2. Alcohol alone is too slow.

Teacher's Note:
1. Revise the physical properties such as hydrogen bonding and boiling points together with the chemistry.
2. Compare similar compounds in pairs when you are asked to rank them.

Answer: (a) C₃H₇COOH

Explanation:
1. C₃H₇MgBr + CO₂ → C₃H₇COOMgBr, which on hydrolysis gives butanoic acid, one carbon more than the Grignard alkyl group.

Teacher's Note:
1. Learn the reactivity order of acid derivatives: acyl chloride, anhydride, ester, amide.
2. Most questions of this type are solved by recalling the standard reagent and product pair.

Answer: (b) propanoic acid

Explanation:
1. C₂H₅MgBr + CO₂ → C₂H₅COOMgBr, and hydrolysis gives propanoic acid.

Teacher's Note:
1. Always link acid strength to the stability of the carboxylate ion.
2. Electron-withdrawing groups increase acidity and electron-donating groups decrease it.

Answer: (c) CH₃COONa

Explanation:
1. CH₃COCl + CH₃COONa → (CH₃CO)₂O + NaCl.

Teacher's Note:
1. Note the name reaction and write its equation once in your notebook.
2. Such one-step recall questions are common in the JEE and NEET style papers.

Answer: (a) acetic acid

Explanation:
1. CH₃CONH₂ + H₂O → CH₃COOH + NH₃ (as ammonium acetate under acid or alkali).

Teacher's Note:
1. Count carbons before and after the reaction to avoid mistakes in chain-length changes.
2. Check whether the reagent is a reducing, oxidising or dehydrating agent before choosing the product.

Answer: (b) ethyl chloroformate

Explanation:
1. Ethyl chloroformate, ClCOOC₂H₅, reacts with one equivalent of CH₃MgI by replacing Cl with CH3.
2. The product is CH₃COOC₂H₅.

Teacher's Note:
1. Eliminate options by checking functional groups on both sides of the reaction.
2. Only one option will have the correct functional group and carbon skeleton.

Answer: (c) acetic anhydride

Explanation:
1. The carboxylate attacks the acyl chloride, giving the anhydride and NaCl.

Teacher's Note:
1. Revise the physical properties such as hydrogen bonding and boiling points together with the chemistry.
2. Compare similar compounds in pairs when you are asked to rank them.

Answer: (a) acetamide

Explanation:
1. Ammonium acetate loses water on heating, giving acetamide.

Teacher's Note:
1. Learn the reactivity order of acid derivatives: acyl chloride, anhydride, ester, amide.
2. Most questions of this type are solved by recalling the standard reagent and product pair.

Answer: (b) esters

Explanation:
1. Two aldehyde molecules with aluminium alkoxide combine to give an ester.

Teacher's Note:
1. Always link acid strength to the stability of the carboxylate ion.
2. Electron-withdrawing groups increase acidity and electron-donating groups decrease it.

Answer: (b) an ester

Explanation:
1. RCOOAg + R'X → RCOOR' + AgX.

Teacher's Note:
1. Note the name reaction and write its equation once in your notebook.
2. Such one-step recall questions are common in the JEE and NEET style papers.

Answer: (c) Hell-Volhard-Zelinsky reaction

Explanation:
1. An acid with Br2 and red phosphorus is brominated at the alpha carbon (Hell-Volhard-Zelinsky reaction).

Teacher's Note:
1. Count carbons before and after the reaction to avoid mistakes in chain-length changes.
2. Check whether the reagent is a reducing, oxidising or dehydrating agent before choosing the product.

Answer: (a) succinic anhydride

Explanation:
1. Dicarboxylic acids that can form a five-membered ring lose water to give the cyclic anhydride.

Teacher's Note:
1. Eliminate options by checking functional groups on both sides of the reaction.
2. Only one option will have the correct functional group and carbon skeleton.

Answer: (d) salicylic acid

Explanation:
1. A = sodium phenoxide.
2. B = sodium salicylate (Kolbe-Schmitt reaction).
3. Acidification gives salicylic acid, C.

Teacher's Note:
1. Revise the physical properties such as hydrogen bonding and boiling points together with the chemistry.
2. Compare similar compounds in pairs when you are asked to rank them.

Answer: (b) an anhydride

Explanation:
1. RCOCl + R'COONa → RCOOCOR' + NaCl, a mixed or simple anhydride.

Teacher's Note:
1. Learn the reactivity order of acid derivatives: acyl chloride, anhydride, ester, amide.
2. Most questions of this type are solved by recalling the standard reagent and product pair.

Answer: (b) CO₂

Explanation:
1. CH3MgI adds to CO₂ to give CH₃COOMgI.
2. Hydrolysis gives CH₃COOH and Mg(OH)I.

Teacher's Note:
1. Always link acid strength to the stability of the carboxylate ion.
2. Electron-withdrawing groups increase acidity and electron-donating groups decrease it.

Answer: (a) CH₃COOH

Explanation:
1. Nitrous acid converts a primary amide to the acid with evolution of N2: RCONH₂ + HNO₂ → RCOOH + N₂ + H₂O.

Teacher's Note:
1. Note the name reaction and write its equation once in your notebook.
2. Such one-step recall questions are common in the JEE and NEET style papers.

Answer: (b) carboxylic acid

Explanation:
1. RCHO → RCOOH on oxidation.

Teacher's Note:
1. Count carbons before and after the reaction to avoid mistakes in chain-length changes.
2. Check whether the reagent is a reducing, oxidising or dehydrating agent before choosing the product.

Answer: (d) both KMnO₄ and K₂Cr₂O₇

Explanation:
1. Both are strong oxidants that convert the side-chain CH₃ to COOH.
2. Sulphuric acid alone is not an oxidant for this.

Teacher's Note:
1. Eliminate options by checking functional groups on both sides of the reaction.
2. Only one option will have the correct functional group and carbon skeleton.

Answer: (c) (CH₃CO)₂O

Explanation:
1. The Perkin reaction condenses an aromatic aldehyde with an acid anhydride in the presence of the sodium salt of the same acid.
2. X is acetic anhydride.

Teacher's Note:
1. Revise the physical properties such as hydrogen bonding and boiling points together with the chemistry.
2. Compare similar compounds in pairs when you are asked to rank them.

Answer: (b) Kolbe's reaction

Explanation:
1. Sodium phenoxide with CO₂ under pressure followed by acidification (Kolbe-Schmitt) gives salicylic acid.

Teacher's Note:
1. Learn the reactivity order of acid derivatives: acyl chloride, anhydride, ester, amide.
2. Most questions of this type are solved by recalling the standard reagent and product pair.