CUET UG Chemistry Booster Test -2 Carboxylic Acids (Structure, Properties, Reactions & Uses)

The carboxyl group (–COOH) is composed of a carbonyl group (C=O) and a hydroxyl group (–OH) attached to the same carbon atom. Carboxylic acids readily form important derivatives such as: Anhydrides Esters Amides The carboxyl group may be attached to: An alkyl group (aliphatic acids) An aryl group (aromatic acids) The carboxyl carbon is sp² hybridized due to resonance and trigonal planar geometry. Therefore, statements A, B and D are correct.

A straight-chain dicarboxylic acid contains two carboxyl groups attached at the ends of a carbon chain. General formula: [ HOOC-(CH_2)_n-COOH ] Examples: Ethanedioic acid (Oxalic acid) Butanedioic acid (Succinic acid) Hexanedioic acid (Adipic acid) Hence option B is correct.

Higher members of aliphatic carboxylic acids are commonly known as fatty acids. Examples: Lauric acid (C12) Palmitic acid (C16) Stearic acid (C18) These acids occur naturally as esters of glycerol in fats and oils. Therefore the typical carbon range is: C12 – C18

Structure: C6H5CH2COOH The principal functional group is –COOH. Parent chain: Ethanoic acid (2 carbon atoms) Substituent: Phenyl group at carbon-2 Therefore the IUPAC name is: 2-Phenylethanoic acid (Common name: Phenylacetic acid)

Phthalic acid has the structure: C6H4(COOH)2 with the two carboxyl groups located at positions 1 and 2 on the benzene ring. Thus its IUPAC name is: Benzene-1,2-dicarboxylic acid Related compounds: Isophthalic acid → Benzene-1,3-dicarboxylic acid Terephthalic acid → Benzene-1,4-dicarboxylic acid

The increasing order of carbon chain length is: Common Name — IUPAC Name — Carbon Atoms Formic acid — Methanoic acid — 1 Acetic acid — Ethanoic acid — 2 Propionic acid — Propanoic acid — 3 Butyric acid — Butanoic acid — 4 Therefore: Formic acid < Acetic acid < Propionic acid < Butyric acid So the correct order is: (B), (D), (C), (A)

The passage states that the bonds to the carboxyl carbon lie in one plane and are separated by about 120°. These features are characteristic of sp² hybridisation and trigonal planar geometry.

The passage explains that the lone pair of electrons on the hydroxyl oxygen delocalizes toward the carbonyl carbon. This resonance gives partial double bond character to the C–O bond and reduces the electrophilic nature of the carboxyl carbon.

1-Decanol is a primary alcohol. When treated with chromic acid/Jones reagent, it undergoes strong or vigorous oxidation to form decanoic acid. CH3(CH2)8CH_2OH O CH3(CH2)8COOH

The oxidation sequence of a primary alcohol is: Primary alcohol Aldehyde Carboxylic acid Therefore, aldehyde is the intermediate during the conversion of a primary alcohol into a carboxylic acid.

The hydrolysis of nitriles proceeds in two stages: [ R-CN \rightarrow R-CONH_2 \rightarrow R-COOH ] H⁺ or OH⁻ acts as a catalyst. The first intermediate formed is an amide. Further heating with acid or base converts the amide into the corresponding carboxylic acid. Therefore statements A, B and D are correct.

Grignard reagents contain a highly nucleophilic carbon atom. RMgX + CO2 RCOO-MgX+ The nucleophilic carbon attacks the electrophilic carbon of carbon dioxide, producing a carboxylate salt. Acidification then yields the corresponding carboxylic acid. Hence the reaction is classified as nucleophilic addition.

Carboxylic acids form two intermolecular hydrogen bonds between two molecules, producing stable cyclic dimers. As a result: They show stronger association than alcohols. They exist largely as dimers in the vapour phase. They also exist as dimers in aprotic solvents such as benzene. Therefore statements A, C and D are correct.

Carboxylic Acid — Solubility Methanoic acid — Miscible in all proportions Pentanoic acid — Slightly soluble Benzoic acid — Nearly insoluble Stearic acid — Practically insoluble wax-like solid Therefore: 1-a, 2-b, 3-c, 4-d

Approximate pKa values: Compound — pKa Acetic acid — 4.76 Benzoic acid — 4.19 Trichloroacetic acid — 0.70 Trifluoroacetic acid — 0.23 Decreasing pKa (weakest acid → strongest acid): [ \text{Acetic acid} > \text{Benzoic acid} > \text{Trichloroacetic acid} > \text{Trifluoroacetic acid} ] Therefore: (A), (C), (B), (D)

The acidity of carboxylic acids depends on the stability of the carboxylate ion formed after loss of H⁺. Chlorine atoms withdraw electron density through the inductive effect (-I effect) and stabilize the negative charge on the carboxylate ion. Acidity increases as the number of chlorine atoms increases: Acetic acid (CH₃COOH) Chloroacetic acid (ClCH₂COOH) Dichloroacetic acid (Cl₂CHCOOH) Trichloroacetic acid (Cl₃CCOOH) Therefore: Acetic acid < Chloroacetic acid < Dichloroacetic acid < Trichloroacetic acid Hence the increasing order of acidity is: (D) → (A) → (B) → (C)

Esterification is represented as: [ RCOOH + R'OH \rightleftharpoons RCOOR' + H_2O ] Since the reaction is reversible, the yield of ester can be increased by: Removing water as it forms, or Distilling out the ester. According to Le Chatelier's principle, removing products shifts equilibrium toward the product side.

Sodalime is prepared by mixing: Sodium hydroxide (NaOH) Calcium oxide (CaO) in the ratio: [ \text{NaOH : CaO} = 3 : 1 ] It is commonly used to remove carbon dioxide from sodium salts of carboxylic acids, producing hydrocarbons with one less carbon atom.

Application — Carboxylic Acid 1. Nylon-6,6 production — a. Hexanedioic acid 2. Perfumery blending — b. Esters of benzoic acid 3. Rubber and electroplating industries — c. Methanoic acid 4. Soaps and detergents — d. Higher fatty acids Therefore: 1-a, 2-b, 3-c, 4-d

Vinegar contains about 5–8% ethanoic acid (acetic acid) in water. [ CH_3COOH ] Ethanoic acid gives vinegar its characteristic sour taste and odor and is extensively used in food processing and preservation.