Aldehydes Ketones and Carboxylic Acids Class 12 Chemistry Exam Questions

Please refer to the below Aldehydes, Ketones and Carboxylic Acids important questions for Class 12 Chemistry. These questions and answers have been prepared as per the latest NCERT Book for Class 12 Chemistry. Students should go through chapter wise Class 12 Chemistry Important Questions designed as per the latest examination pattern issued by CBSE.

Very Short Answer Questions :

Question. Predict the organic product of the following reactions :

Answer : 

Question. Write the IUPAC name of the compound :

Answer : 

Question. Give simple chemical test to distinguish between :
(a) Pentan-2-one and Pentan-3-one.
(b) Ethanal and Propanal 
Answer : 

Question. Write the IUPAC name of the compound :

Answer : 

Question. How would you account for the following :
The boiling points of aldehydes and ketones are lower than of the corresponding acids.
Answer : The boiling points of aldehydes and ketones are lower than that of corresponding alcohols and acids due to absence of intermolecular H–bonding in aldehydes and ketones.

Question. Write Cannizzaro reaction giving an example.
Answer : Cannizzaro’s reaction : Aldehydes which do not contain a-H atom undergo disproportionation when heated with concentrated (50 %) NaOH.

Question. Write the IUPAC name of the following :

Answer : 

Question. Draw the structure of the following derivatives :
(i) Propanone oxime
(ii) Semicarbazone of the CH₃CHO
Answer : 

Question. Give simple chemical tests to distinguish between the following pair of compounds.
Propanal and Butan-2-one
Answer : Propanal and Butan-2-one can be distinguised by their reactions with tollen’s reagent. Propanal will form the silver mirror, but Butan-2-one does not react. 

Question. Give reason :
Aldehydes are more reactive than ketones towards nucleophilic reagents. 
Answer : Ketones are less reactive than aldehydes towards nucleophilic addition reactions because :
The two electron releasing alkyl groups decrease the magnitude of positive charge on carbonyl carbon and make it less susceptible to nucleophilic attack.

Question. How will you obtain the following :
Benzaldehyde from Phenol 
Answer : 

Question. Draw the structure of 3-methylpentanal.
Answer : 

Question. Write the structure of the product formed in the following reaction :

Answer : 

Question. Arrange the following compounds in an increasing order of their reactivity in nucleophilic addition reactions : ethanal, propanal, propanone, butanone.
Answer : Butanone < propanone < propanal < ethanal.

Question. Account for the following :
(i) CH₃CHO is more reactive than CH₃COCH₃ towards reaction with HCN.
(ii) There are two –NH₂ groups in semicarbazide (H₂NNHCONH₂). However, only one is involved in the formation of semicarbazone. 
Answer : (i) It is a nucleophilic addition reaction, in which CN^– acts as a nucleophile. CH₃CHO undergoes nucleophilic addition reactions faster than CH₃COCH₃ as in CH₃COCH₃ there are two electron releasing methyl groups attached to the carbonyl carbon that hinders the approach of nucleophile to  carbonyl carbon and reduce the electrophilicity of the carbonyl group while in CH₃CHO, there is only one methyl group attached to carbonyl carbon.
(ii) Semicarbazide has the following resonance structures arising due to the electron withdrawing nature of the O atom.

Lone pairs of N-1 and N-2 are involved in conjugation with >C=O group while that of N-3 is not involved in resonance thus, it is involved in the formation of semicarbazone.

Question. Illustrate the following name reactions giving a chemical equations in each case :
(i) Clemmensen reaction
(ii) Cannizzaro’s reaction 
Answer : (i) Clemmensen reduction : The carbonyl group of aldehydes and ketones is reduced to  CH₂ group on treatment with zinc amalgam and concentrated hydrochloric acid.

(ii) Cannizzaro’s reaction : Aldehydes which do not contain a-H atom undergo disproportionation when heated with concentrated (50 %) NaOH.

Question. Complete the following reactions :

Answer : (i) 

(ii) 

Question. Predict the products of the following reactions :

Answer : 

Question. (a) Write the chemical reaction involved in Wolff-Kishner reduction.
(b) Arrange the following in the increasing order of their reactivity towards nucleophilic addition reaction.
C₆H₅COCH₃, CH₃ — CHO, CH₃COCH₃
(c) A and B are two functional isomers of compound C₂H₆O. On heating with NaOH and I₂, isomer B forms yellow precipitate of iodoform whereas isomer A does not form any precipitate. Write the formulae of A and B.
Answer : Wolff-Kishner reduction reaction : The carbonyl group of aldehydes and ketones is reduced to CH₂ group on treatment with hydrazine followedby heating with potassium hydroxide in a high
boiling solvent such as ethylene glycol.

(ii) Increasing order of reactivity towards nucleophilic addition reaction :
C₆H₅COCH₃ < CH₃COCH₃ < CH₃CHO
(iii) Formula of compounds A and B = C₃H₆O B forms yellow precipitate of iodoform. Hence, B must contain —COCH₃ group. Therefore, compound ‘B’ must be .

A does not give iodoform test and it is functional isomer of B thus, it may be CH₃CH₂CHO.

Question. How do you convert the following :
Ethyne to Ethanal 
Answer : 

Question. Write the IUPAC name of the following :
CH₃—CH₂—CHO 
Answer : 

Question. How will you convert the following :
(i) Propanone to Propan-2-ol
(ii) Ethanal to 2-hydroxy propanoic acid
Answer : 

Question. How will you convert ethanal into the following compounds? Give the chemical equations involved.

Answer : 

Question. Write the IUPAC name of the following :

Answer : 

Short Answer Questions :

Question. Give simple chemical tests to distinguish between the following pair of compounds :
Ethanal and Propanal
Answer : Ethanal and propanal can be distinguished by iodoform test.
Yellow precipitate of iodoform will be formed from ethanal on heating with iodine and sodium hydroxide solution.

Question. Write the IUPAC name of the following compound :

Answer : 

Question. Give chemical tests to distinguish between the following pairs of compunds :
Benzaldehyde and Acetophenone.
Answer : Benzaldehyde and acetophenone can be distinguished by Tollens’ test.
Benzaldehyde will form silver mirror, on treatment with Tollens’ reagent whereas acetophenone will not show Tollens’ Test.

Question. Explain the mechanism of a nucleophilic attack on the carbonyl group of an aldehyde or a ketone.
Answer : Mechanism of nucleophilic addition reactions : Nucleophile attacks from the top face :

A nucleophile attacks the electrophilic carbon atom from a direction perpendicular to the plane of sp² hybridised orbital of carbonyl carbon. The hybridisation of carbon changes from sp² to sp³ in this process and a tetrahedral alkoxide intermediate is produced.
This intermediate captures a proton from the reaction medium to give the electrically neutral product. The net result is addition of Nu– and H+ across the carbon oxygen double bond.

Question. Draw the structural formula of 1-phenyl Propan-1-one molecule. 
Answer : 

Question. Write the IUPAC name of the following :

Answer : 

Question. Write the structure of A and B in the following reaction :

Answer : 

Question. Name the reagents used in the following reactions :
(i) CH₃—CO—CH₃ →^? CH₃—CH—CH₃
                                          l
                                        OH
Answer : (i) Lithium aluminium hydride (LiAlH₄).

Question. Predict the products of the following reactions :

Answer : 

Question. Give a chemical equation for each, illustrate the following processes :
(i) Cannizzaro reaction
(ii) Acetylation 
Answer : (i) Cannizzaro’s reaction : Aldehydes which do not contain a-H atom undergo disproportionation when heated with concentrated (50 %) NaOH.

(ii) Acetylation : Introduction of acetyl group

in alcohols, phenols or amines is called their acetylation.    

Question. Write the structure of 3-methyl butanal.
Answer : 

Question. Draw the structures of the following :
(i) p-Methylbenzaldehyde
(ii) 4-Methylpent-3-en-2-one 
Answer : 

Question. Identify A, B, C, D and E in following sequence of reactions :

Answer : 

Question. Account for the following :
CH₃CHO is more reactive than CH₃COCH₃ towards reaction with HCN. 
Answer : It is a nucleophilic addition reaction, in which CN – acts as a nucleophile. CH₃CHO undergoes nucleophilic addition reactions faster than CH₃COCH₃ as in CH₃COCH₃ there are two electron releasing methyl groups attached to the carbonyl carbon that hinders the approach of nucleophile to carbonyl carbon and reduce the electrophilicity of the carbonyl group while in CH₃CHO, there is only one methyl group attached to carbonyl carbon.

Question. Predict the products of the following reactions:

Answer : 

Question. How is following obtained?
Benzaldehyde from toluene. 
Answer : 

Question. Write the structure of 2-methylbutanal.
Answer :

Question. What is Tollens’ reagent? Write one usefulness of this reagent.
Answer : Tollens’ reagent is an ammoniacal silver nitrate solution.
Tollens’ reagent is used to test an aldehyde. Both aliphatic and aromatic aldehydes reduce Tollens’ reagent and give silver mirror.

Question. Write the main product in the following equations :

Answer : 

Question. Complete each synthesis by giving the missing material, reagent or products:

Answer : (i)

(ii) 

Question. Write one chemical equation for each to illustrate the following reactions :
(i) Rosenmund’s reduction
(ii) Cannizzaro reaction 
Answer : (i) 

(ii) Cannizzaro’s reaction : Aldehydes which do not contain a-H atom undergo disproportionation when heated with concentrated (50 %) NaOH.

Question. Write the structure of 4-chloropentan-2-one.
Answer : 

Question. Give chemical tests to distinguish between :
(i) Acetaldehyde and benzaldehyde
(ii) Propanone and propanal. 
Answer : (i) Distinction between acetaldehyde and benzaldehyde : Acetaldehyde and benzaldehyde can be distinguish by Fehling solution.
Acetaldehyde gives red coloured precipitate with Fehling solution while benzaldehyde does not.

(ii) Propanal and propanone can be distinguished by their reactions with Tollens’ reagent.
Propanal will form the silver mirror, but propanone does not react.

Question. Give chemical tests to distinguish between
(i) Propanal and propanone
(ii) Benzaldehyde and acetophenone
Answer : (i) ropanal and propanone can be distinguished by their reactions with Tollens’ reagent.
Propanal will form the silver mirror, but propanone does not react.
(ii) Benzaldehyde and acetophenone can be distinguished by Tollens’ test.
Benzaldehyde will form silver mirror, on treatment with Tollens’ reagent whereas acetophenone will not show Tollens’ Test.

Question. Describe the following reactions :
(i) Acetylation
(ii) Aldol condensation 
Answer : (i) Acetylation : Introduction of acetyl group

in alcohols, phenols or amines is called their acetylation.
(ii) Aldol condensation : Two molecules of an aldehyde or ketones having at least one a-hydrogen atom condense in the presence of a dilute alkali to give b-hydroxyaldehyde or b-hydroxyketone which upon heating give a,b-unsaturated aldehyde or ketone.

Question. Arrange the following compounds in an increasing order of their property as indicated :
Acetaldehyde, acetone, methyl tert-butyl ketone (reactivity towards HCN) 
Answer : 

Question. Write the IUPAC name of the following compound

Answer : 

Question. How would you account for the following
(i) Aldehydes are more reactive than ketones toward nucleophiles.
(ii) The aldehydes and ketones undergo a number of addition reactions.
Answer : (i) Ketones are less reactive than aldehydes towards nucleophilic addition reactions because :
The two electron releasing alkyl groups decrease the magnitude of positive charge on carbonyl carbon and make it less susceptible to nucleophilic attack.

The two bulkier alkyl groups hinder the approach of the nucleophile to the carbonyl carbon. This is called steric factor.
(ii) Aldehydes and ketones undergo a number of addition reactions as both possess the carbonyl functional group which reacts with a number of nucleophiles such as HCN, NaHSO₃, alcohols, ammonia derivatives and Grignard reagents.