🔥 Aldehyde, Ketone Important Questions - Class 12 Boards 2026
Class 12 Chemistry: Aldehydes, Ketones Important Questions for Board 2026
Here are Top 10 Important Questions of Aldehydes, Ketones and Carboxylic Acids. These are most expected for CBSE & Bihar Board 2026 [5 Marks Fixed].
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Q1. What are Aldehydes and Ketones? General Formula?
Ans: Aldehydes contain -CHO group (R-CHO) and Ketones contain >C=O group (R-CO-R'). Both have carbonyl functional group. Example: Formaldehyde (HCHO), Acetone (CH3COCH3).
Q2. Why aldehydes & ketones have higher boiling point than hydrocarbons?
Ans: Due to polar carbonyl group, they have dipole-dipole attraction, which is stronger than Van der Waals forces in non-polar hydrocarbons.
Q3. What is Cannizzaro Reaction?
Ans: Aldehydes having no alpha-H, on treatment with conc. NaOH give alcohol and salt of acid.
2HCHO + NaOH → CH3OH + HCOONa
Q4. What is Aldol Condensation?
Ans: Aldehydes/Ketones with alpha-H in presence of dil. NaOH give β-hydroxy carbonyl compound.
2CH3CHO → CH3CH(OH)CH2CHO (Aldol)
Q5. Tollen's Test - How to distinguish aldehyde and ketone?
Ans: Aldehyde gives silver mirror with Tollen's reagent [Ag(NH3)2]+ OH-, ketone does not react.
Reaction: R-CHO + 2[Ag(NH3)2]+ + 3OH- → RCOO- + 2Ag (Silver Mirror) + 4NH3 + 2H2O
Result: Silver mirror at the inner wall of test tube confirms aldehyde.
Q6. What is Rosenmund Reduction? Give equation.
Ans: It is a method to prepare aldehyde from acid chloride. Acid chloride is reduced with H2 gas in presence of Pd catalyst poisoned with BaSO4.
Equation: R-COCl + H2 --(Pd/BaSO4)--> R-CHO + HCl
Example: CH3COCl + H2 → CH3CHO + HCl
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Q7. What is Stephen Reaction?
Ans: It is a method to prepare aldehyde from alkyl cyanide. Nitrile is reduced with SnCl2 and HCl to aldimine, which on hydrolysis gives aldehyde.
Equation: R-C≡N + SnCl2 + 2HCl → R-CH=NH.HCl → [H2O] → R-CHO
Example: CH3CN → CH3CHO (Acetaldehyde)
Q8. Why carboxylic acid has higher boiling point than aldehyde and ketone?
Ans: Carboxylic acids have -OH group, so they form intermolecular Hydrogen Bonding. They exist as dimer (two molecules joined). Due to this strong H-bonding, more heat is required to break it, hence higher boiling point than aldehydes/ketones which have only dipole-dipole forces.
Q9. What is Hell-Volhard-Zelinsky (HVZ) Reaction?
Ans: Carboxylic acids having alpha-Hydrogen, when treated with Chlorine or Bromine in presence of Red Phosphorus, give alpha-halo carboxylic acid.
Equation: CH3COOH + Cl2 --(Red P)--> ClCH2COOH + HCl
Use: To prepare alpha-halo acids.
Q10. What is Haloform Reaction? How to convert Acetone to Chloroform?
Ans: Compounds containing CH3CO- group (methyl ketones) react with halogen and NaOH to give Haloform (CHX3).
Reaction (Acetone to Chloroform):
CH3COCH3 + 3Cl2 + 4NaOH → CHCl3 + CH3COONa + 3NaCl + 3H2O
CHCl3 is Chloroform. Iodoform test is also an example of this reaction.
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