JEE Chemistry Aldehydes Ketones And Carboxylic Acids MCQs Set 21

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Chapter-wise Objective Questions: Aldehydes Ketones and Carboxylic Acids

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Multiple Choice Questions

Question 1: The OH group of an alcohol or the COOH group of a carboxylic acid can be replaced by Cl using
(a) chlorine
(b) hydrochloric acid
(c) phosphorus pentachloride
(d) hypochlorous acid
Show Answer & Explanation

Answer: (c) phosphorus pentachloride

Explanation:
1. PCl5 replaces both -OH of alcohol and -OH of -COOH by -Cl.

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.

Question 2: Which is most acidic?
(a) picric acid
(b) p-nitrophenol
(c) m-nitrophenol
(d) 2,4-dinitrophenol
Show Answer & Explanation

Answer: (a) picric acid

Explanation:
1. Three nitro groups (ortho and para) stabilise the phenoxide most.
2. Picric acid pKa is about 0.4.

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.

Question 3: Benedict's solution is not reduced by
(a) formaldehyde
(b) acetaldehyde
(c) glucose
(d) acetic anhydride
Show Answer & Explanation

Answer: (d) acetic anhydride

Explanation:
1. Acetic anhydride has no aldehyde or alpha-hydroxy ketone group.

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.

Question 4: CH3COOH reacted with CH≡CH in the presence of Hg2+ gives
(a) ethyl acetate
(b) vinyl acetate only
(c) ethylidene diacetate, CH3CH(OOCCH3)2
(d) none of these
Show Answer & Explanation

Answer: (c) ethylidene diacetate, CH3CH(OOCCH3)2

Explanation:
1. Acetic acid adds to ethyne to give vinyl acetate, which adds another molecule of acid.
2. The final product is ethylidene diacetate.

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.

Question 5: Acetic acid reacts with PCl5 to form
(a) CH3COCl
(b) CHCl2COOH
(c) CH2ClCOOH
(d) CH3COOCl
Show Answer & Explanation

Answer: (a) CH3COCl

Explanation:
1. CH3COOH + PCl5 → CH3COCl + POCl3 + HCl.

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.

Question 6: CH3COOC2H5 with excess C2H5MgBr and hydrolysis gives
(a) CH3-C(=O)-C2H5
(b) CH3-C(OH)(C2H5)2
(c) CH3-C(=O)-CH3
(d) (CH3)2C(OH)-C2H5
Show Answer & Explanation

Answer: (b) CH3-C(OH)(C2H5)2

Explanation:
1. The ester adds two equivalents of the Grignard reagent through the intermediate ketone.
2. The product is 3-methylpentan-3-ol.

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.

Question 7: CH3CHO → (HCN) A → (H2O) B. The product B is
(a) malonic acid
(b) glycolic acid
(c) lactic acid
(d) malic acid
Show Answer & Explanation

Answer: (c) lactic acid

Explanation:
1. A = CH3CH(OH)CN.
2. Hydrolysis gives CH3CH(OH)COOH, lactic 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.

Question 8: Fruity smell is given by
(a) esters
(b) alcohols
(c) chloroform
(d) acid anhydrides
Show Answer & Explanation

Answer: (a) esters

Explanation:
1. Low-molar-mass esters have pleasant fruity odours.

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.

Question 9: A lactic acid molecule has
(a) one chiral carbon atom
(b) two chiral carbon atoms
(c) no chiral carbon atom
(d) an asymmetric centre absent
Show Answer & Explanation

Answer: (a) one chiral carbon atom

Explanation:
1. In CH3-CH(OH)-COOH the middle carbon bears four different groups.

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.

Question 10: In a set of reactions, CH3COOH → (SOCl2) A → (benzene, AlCl3) B → (HCN) C → (HOH) D. The product D is
(a) 2-hydroxy-2-phenylpropanoic acid
(b) C6H5-C(CH3)(OH)-CN
(c) acetophenone
(d) 1-phenylethanol
Show Answer & Explanation

Answer: (a) 2-hydroxy-2-phenylpropanoic acid

Explanation:
1. A = acetyl chloride; B = acetophenone (Friedel-Crafts acylation).
2. C = cyanohydrin; hydrolysis converts CN to COOH, giving C6H5C(CH3)(OH)COOH.

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.

Question 11: C6H5CHO + HCN → C6H5CH(OH)CN. The product would be
(a) a racemate
(b) optically active
(c) a meso compound
(d) a mixture of diastereomers
Show Answer & Explanation

Answer: (a) a racemate

Explanation:
1. CN- attacks the planar carbonyl equally from both faces, giving equal amounts of the two enantiomers.
2. Without any chiral reagent the product is racemic and optically inactive.

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.

Question 12: CH3CO2C2H5 on reaction with sodium ethoxide in ethanol gives A, which on heating with acid gives B. B is
(a) CH3COCH2COOH
(b) CH3COCH3
(c) cyclobutane-1,3-dione type ring
(d) CH2=C(OC2H5)2
Show Answer & Explanation

Answer: (b) CH3COCH3

Explanation:
1. A = ethyl acetoacetate (Claisen condensation).
2. Acid hydrolysis and heating (ketonic hydrolysis) gives acetoacetic acid, which loses CO2 to give acetone.

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.

Question 13: C6H5CONHCH3 can be converted into C6H5CH2NHCH3 by
(a) NaBH4
(b) H2/Pd-C
(c) LiAlH4
(d) Zn-Hg/HCl
Show Answer & Explanation

Answer: (c) LiAlH4

Explanation:
1. Amides are reduced to amines by LiAlH4.
2. NaBH4 and catalytic hydrogenation do not reduce the amide.

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.

Question 14: Among the following acids, which has the lowest pKa value?
(a) CH3COOH
(b) HCOOH
(c) (CH3)2CH-COOH
(d) CH3CH2COOH
Show Answer & Explanation

Answer: (b) HCOOH

Explanation:
1. Alkyl groups donate electrons and weaken acidity, so formic acid, with no alkyl group, is strongest.

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.

Question 15: X is heated with soda lime and gives ethane. X is
(a) ethanoic acid
(b) methanoic acid
(c) propanoic acid
(d) either (a) or (c)
Show Answer & Explanation

Answer: (c) propanoic acid

Explanation:
1. Decarboxylation removes one carbon as carbonate: C2H5COOH → C2H6.
2. Ethanoic acid would give methane.

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.

Question 16: Which of the following is an amphoteric acid?
(a) glycine
(b) salicylic acid
(c) benzoic acid
(d) citric acid
Show Answer & Explanation

Answer: (a) glycine

Explanation:
1. Glycine has both an acidic COOH and a basic NH2 group.

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.

Question 17: Colouration of Br2/CCl4 will be discharged by
(a) cinnamic acid
(b) benzoic acid
(c) o-phthalic acid
(d) acetophenone
Show Answer & Explanation

Answer: (a) cinnamic acid

Explanation:
1. Cinnamic acid has a C=C double bond in its side chain, which adds bromine.

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.

Question 18: Order of hydrolysis: (I) RCOCl (II) RCOOR (III) RCONH2 (IV) (RCO)2O.
(a) I > IV > II > III
(b) I > II > III > IV
(c) I > III > II > IV
(d) IV > III > II > I
Show Answer & Explanation

Answer: (a) I > IV > II > III

Explanation:
1. Reactivity decreases in the order acyl chloride, anhydride, ester, amide.

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.

Question 19: Which of the following reacts with NaHCO3 to give the sodium salt and CO2?
(a) acetic acid
(b) n-hexanol
(c) phenol
(d) both acetic acid and phenol
Show Answer & Explanation

Answer: (a) acetic acid

Explanation:
1. Acetic acid is a stronger acid than carbonic acid.
2. Phenol and alcohol are weaker and do not react.

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.

Question 20: A carboxylic acid is converted into its anhydride using
(a) thionyl chloride
(b) sulphur chloride
(c) sulphuric acid
(d) phosphorus pentoxide
Show Answer & Explanation

Answer: (d) phosphorus pentoxide

Explanation:
1. P2O5 is a strong dehydrating agent: 2RCOOH → (RCO)2O + H2O.

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.

Question 21: The following compound (aspirin, 2-acetoxybenzoic acid) is used as
(a) an anti-inflammatory agent
(b) an analgesic
(c) a hypnotic
(d) an antiseptic
Show Answer & Explanation

Answer: (b) an analgesic

Explanation:
1. Aspirin relieves pain (analgesic) and also reduces fever.

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.

Question 22: To which of the following groups does soap belong?
(a) esters
(b) amines
(c) salts of organic higher fatty acids
(d) aldehydes
Show Answer & Explanation

Answer: (c) salts of organic higher fatty acids

Explanation:
1. Soaps are sodium or potassium salts of higher fatty acids.

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.

Question 23: Aspirin is an acetylation product of
(a) o-hydroxybenzoic acid
(b) o-dihydroxybenzene
(c) m-hydroxybenzoic acid
(d) p-dihydroxybenzene
Show Answer & Explanation

Answer: (a) o-hydroxybenzoic acid

Explanation:
1. Salicylic acid (o-hydroxybenzoic acid) acetylated at OH gives aspirin.

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.

Question 24: Which one is used as a food preservative?
(a) sodium acetate
(b) sodium propionate
(c) sodium benzoate
(d) sodium oxalate
Show Answer & Explanation

Answer: (c) sodium benzoate

Explanation:
1. Sodium benzoate is widely used to preserve food and soft drinks.

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.

Question 25: What makes a lemon sour?
(a) tartaric acid
(b) oxalic acid
(c) citric acid
(d) hydrochloric acid
Show Answer & Explanation

Answer: (c) citric acid

Explanation:
1. Lemon juice contains citric 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.

Question 26: The reagent used for protection of the amino group during nitration of aniline is
(a) SOCl2/pyridine
(b) PCl5
(c) acetic acid
(d) acetic anhydride
Show Answer & Explanation

Answer: (d) acetic anhydride

Explanation:
1. Acetylation with acetic anhydride gives acetanilide, preventing oxidation and meta substitution.

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.

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Practice MCQs for JEE Chemistry Aldehydes Ketones and Carboxylic Acids

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