Take timed practice tests on Aldehydes, Ketones and Carboxylic Acids for JEE Main and JEE Advanced with session-wise drills, score review, and explanation-led revision.
Six 20-question timed sessions plus a 60-question chapter module. Each item is original and reframed for copyright safety.
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1. The functional group in aldehydes is:
Explanation: Aldehydes contain the −CHO group where the carbonyl carbon is bonded to at least one H. Ketones have the carbonyl carbon bonded to two carbon atoms (−CO−).
2. Tollens' reagent (ammoniacal AgNO₃) distinguishes aldehydes from ketones because:
Explanation: Aldehydes are oxidised by Tollens' reagent: RCHO + 2[Ag(NH₃)₂]⁺ → RCOO⁻ + 2Ag↓ + ... The silver mirror confirms aldehyde. Ketones cannot be oxidised under mild conditions.
3. Nucleophilic addition to carbonyl groups occurs because the carbonyl carbon is:
Explanation: O is more electronegative than C → C=O is polarised with δ⁺ on C and δ⁻ on O. Nucleophiles attack the electrophilic carbonyl carbon.
4. Aldol condensation of ethanal (CH₃CHO) with dilute NaOH gives:
Explanation: In aldol reaction: the α-carbon of one ethanal attacks the carbonyl of another. Product: CH₃CH(OH)CH₂CHO (3-hydroxybutanal). Heating (dehydration) gives but-2-enal (crotonaldehyde).
5. Cannizzaro reaction occurs with aldehydes that have:
Explanation: Cannizzaro reaction: aldehyde with no α-H undergoes disproportionation with conc. NaOH → one molecule oxidised to carboxylate, another reduced to alcohol. 2HCHO → HCOO⁻ + CH₃OH.
6. Carboxylic acids have higher boiling points than alcohols of similar molecular weight because:
Explanation: Carboxylic acids form cyclic H-bonded dimers through two strong O−H···O hydrogen bonds. This effective doubling of molecular mass significantly raises boiling points.
7. The reaction RCOOH + R'OH ⇌ RCOOR' + H₂O in the presence of acid is called:
Explanation: Fischer esterification: carboxylic acid + alcohol + H⁺ catalyst → ester + water. It is reversible (equilibrium); excess alcohol or removal of water drives it to the right.
8. The iodoform test gives a yellow precipitate (CHI₃) with:
Explanation: Iodoform test: I₂/NaOH. Positive for: (1) methyl ketones (CH₃CO−R), (2) CH₃CHOH−R (oxidised to methyl ketone in situ), (3) ethanal (CH₃CHO), (4) ethanol (CH₃CH₂OH). CHI₃ (iodoform) = yellow precipitate with antiseptic smell.
9. The order of reactivity of carbonyl compounds towards nucleophilic addition is:
Explanation: Reactivity decreases as steric hindrance and electron donation from alkyl groups increases. Formaldehyde (no alkyl) is most reactive; ketones (two alkyl groups) least reactive among simple carbonyls.
10. Clemmensen reduction converts a ketone to:
Explanation: Clemmensen reduction: Zn(Hg) amalgam + conc. HCl converts C=O to CH₂. Used in acidic conditions (compare Wolff-Kishner: NH₂NH₂/KOH in basic conditions, same result). Used when base-sensitive groups are absent.
11. Rosenmund reduction of acid chloride (RCOCl + H₂, Pd/BaSO₄) gives:
Explanation: Rosenmund reduction: RCOCl + H₂ → RCHO (aldehyde). The poisoned catalyst (Pd/BaSO₄) prevents further reduction of the aldehyde to alcohol. Used for preparing aldehydes from acid chlorides.
12. The simplest ketone is:
Explanation: Acetone (CH₃COCH₃, propan-2-one) is the simplest ketone with 3 carbon atoms. Formaldehyde = simplest aldehyde, acetic acid = simplest carboxylic acid.
13. Fehling's solution gives a brick-red precipitate with:
Explanation: Fehling's solution (Cu²⁺ in alkaline tartrate) is reduced by aliphatic aldehydes and sugars to Cu₂O (brick-red precipitate). Aromatic aldehydes (benzaldehyde) and ketones do NOT reduce Fehling's.
14. The decarboxylation of RCOONa by sodalime (NaOH + CaO) on heating gives:
Explanation: Dry distillation of sodium salt of carboxylic acid with CaO (soda lime): RCOONa + NaOH → R−H + Na₂CO₃. The decarboxylation removes one carbon as CO₂, giving an alkane with one fewer carbon than the acid.