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CBSE 12th Chemistry Board Exam 2020: Important Questions & Answers from Chapter 12- Aldehydes, Ketones and Carboxylic Acids

Check important questions and answers for the chapter Aldehydes, Ketones and Carboxylic Acids here for the upcoming CBSE Class 12th Chemistry Examination 2020. 

Mar 5, 2020 18:48 IST
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chapter 12
chapter 12

The students who are appearing CBSE Class 12th Chemistry Examination 2020 can go through the below-mentioned important questions for the chapter Aldehydes, Ketones and Carboxylic Acids. The questions and answers mentioned in this article are strictly based on the latest CBSE pattern. 

Key Points to be mentioned while writing the answers to the below mentioned important questions: 

Question 1- Name the reagents used: 

(i)  Hexan-1-ol to hexanal

(ii) Cyclohexanol to cyclohexanone

(iii) p-Fluorotoluene to p-fluorobenzaldehyde

(iv) Ethanenitrile to ethanal

(v) Allyl alcohol to propenal

(vi) But-2-ene to ethanal 

Answer: (i) C5H5NH+CrO3Cl- (PCC)

(ii) K2Cr2O7 in acidic medium

(iii)  CrO3 in the presence of acetic anhydride

(iv) (Diisobutyl)aluminium hydride (DIBAL-H)

(v) PCC

(vi) O3/H2O-Zn dust

Question 2- Arrange the following in the increasing order of their boiling points: 

(i) CH3CH2CH2CHO, CH3CH2CH2CH2OH, H5C2-O-C2H5, CH3CH2CH2CH2CH3

(ii) CH3CHO, CH3CH2OH, CH3OCH3, CH3CH2CH3

Answer: (i) CH3CH2CH2CH2CH3 < H5C2-O-C2H5 < CH3CH2CH2CHO < CH3CH2CH2CH2OH

(ii) CH3CH2CH3 < CH3OCH3 < CH3CHO < CH3CH2OH

Question 3- State the equations for: 

(i)  Wolff-Kishner reduction

(ii)  Etard reaction

(iii) Hell-Volhard-Zelinsky reaction

(iv) Decarboxylation

Answer: (i) 

(ii)

(iii)

(iv)

Question 4- Define: 

(i) Clemmensen reduction

(ii) Cannizzaro reaction

Answer: (i)  The carbonyl group of aldehydes and ketones is reduced to the CH2 group on treatment with zinc amalgam and concentrated hydrochloric acid.

(ii) Aldehydes which do not have an α-hydrogen atom, undergo self oxidation and reduction (disproportionation) reaction on treatment with concentrated alkali. In this reaction, one molecule of the aldehyde is reduced to alcohol while another is oxidised to carboxylic acid salt.

Question 5- Predict the products: 

Answer: 

 

Question 6-  Write chemical reactions to affect the following transformations: 

(i) Butan-1-ol to butanoic acid 

(ii) Benzyl alcohol to phenylethanoic acid

(iii) 3-Nitrobromobenzene to 3-nitrobenzoic acid

Answer: 

Question 7-Write IUPAC names for the following compounds: 

(i) Ph CH2CH2COOH

(ii) (CH3) 2C=CHCOOH

(iii)

(iv)

Answer: (i) 3-Phenylpropanoic acid

(ii) 3-Methylbut-2-enoic acid

(iii) 2-Methylcyclopentanecarboxylic acid

(iv) 2,4,6-Trinitrobenzoic acid

Question 8-  Convert the following compounds to benzoic acid: 

(i) Ethylbenzene

(ii) Acetophenone 

(iii) Bromobenzene 

(iv) Phenylethene (Styrene)

Answer:

 

Question 9- An organic compound (A) with molecular formula C8H8O forms an orange-red precipitate with 2,4-DNP reagent and gives yellow precipitate on heating with iodine in the presence of sodium hydroxide. It neither reduces Tollens’ or Fehlings’ reagent nor does it decolourise bromine water or Baeyer’s reagent. On drastic oxidation with chromic acid, it gives a carboxylic acid (B) having molecular formula C7H6O2. Identify the compounds (A) and (B) and explain the reactions involved.

Answer: (A) forms a 2,4-DNP derivative. Therefore, it is an aldehyde or a ketone. Since it does not reduce Tollens’ or Fehling reagent, (A) must be a ketone. (A) responds to iodoform test. Therefore, it should be a methyl ketone. The molecular formula of (A) indicates a high degree of unsaturation, yet it does not decolourise bromine water or Baeyer’s reagent. This indicates the presence of unsaturation due to an aromatic ring. Compound (B), being an oxidation product of a ketone should be a carboxylic acid. The molecular formula of (B) indicates that it should be benzoic acid and compound (A) should, therefore, be a monosubstituted aromatic methyl ketone. The molecular formula of (A) indicates that it should be phenyl methyl ketone (acetophenone). Reactions are as follows:



Question 10- Give chemical tests to distinguish between the following pairs:

(i) Butanal and Butan-2-one 

(ii) Benzoic acid and Phenol

Answer: (i) Tollens’ reagent test: Add an ammoniacal solution of silver nitrate (Tollens’ Reagent) in both the solutions. Butanal gives silver mirror whereas Butan-2-one does not. 

(ii) Ferric chloride test: Add neutral FeCl3 in both the solutions, phenol reacts with neutral FeCl3 to form an iron-phenol complex giving violet colour but benzoic acid does not.

The above-mentioned list of important questions and answers for CBSE Class 12th Chemistry Examination 2020 is strictly based on the NCERT textbook, sample papers and previous year papers. The students can also go through the links mentioned below: 

CBSE Board Exam 2020: Check Important Questions of Class 12th Chemistry Subject

CBSE 12th Chemistry Board Exam 2020: Important Questions & Answers from All Chapters of NCERT Textbooks - Part I & II

CBSE 12th Chemistry Board Exam 2020: Important Questions & Answers from Chapter 11- Alcohols, Phenols and Ethers

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