Science (English Medium) Class 12 - CBSE Question Bank Solutions for Chemistry

In Kolbe’s reaction, instead of phenol, phenoxide ion is treated with carbon dioxide. Why?

Ethers can be prepared by Williamson synthesis in which an alkyl halide is reacted with sodium alkoxide. Di-tert-butyl ether can’t be prepared by this method. Explain.

Why is the C – O – H bond angle in alcohols slightly less than the tetrahedral angle whereas the C – O – C bond angle in ether is slightly greater?

Assertion: Bond angle in ethers is slightly less than the tetrahedral angle.

Reason: There is a repulsion between the two bulky (–R) groups.

Which of the following compounds is most reactive towards nucleophilic addition reactions?

Which of the following is the correct representation for intermediate of nucleophilic addition reaction to the given carbonyl compound (A):

(i)  

(ii)  

(iii)  

(iv) 

Write a test to differentiate between pentan-2-one and pentan-3-one.

Benzaldehyde can be obtained from benzal chloride. Write reactions for obtaining benzalchloride and then benzaldehyde from it.

Alkenes   and carbonyl compounds , both contain a π bond but alkenes show electrophilic addition reactions whereas carbonyl compounds show nucleophilic addition reactions. Explain.

Carboxylic acids contain carbonyl group but do not show the nucleophilic addition reaction like aldehydes or ketones. Why?

Identify the compounds A, B and C in the following reaction.

\[\ce{CH3 - Br ->[Mg/ether] (A) ->[(i) CO][(ii) Water] (B) ->[CH3OH/H+][Δ] (C)}\]

A primary amine, \[\ce{RNH2}\] can be reacted with \[\ce{CH3-X}\] to get secondary amine, \[\ce{R-NHCH3}\] but the only disadvantage is that 3° amine and quaternary ammonium salts are also obtained as side products. Can you suggest a method where \[\ce{RNH2}\] forms only 2° amine?

Assertion: Acetanilide is less basic than aniline.

Reason: Acetylation of aniline results in decrease of electron density on nitrogen.

Sucrose is dextrorotatory but the mixture obtained after hydrolysis is laevorotatory. Explain.

Identify the type of polymer.

—A—B—B—A—A—A—B—A—

Which of the following chemicals can be added for sweetening of food items at cooking temperature and does not provide calories?

Which of the following will not enhance nutritional value of food?

Which of the following are not used as food preservatives?

(i) Table salt

(ii) Sodium hydrogencarbonate

(iii) Cane sugar

(iv) Benzoic acid

Sugar is the main source of energy as it produces energy on metabolic decomposition. But these days low calorie drinks are more popular, why?

Pickles have a long shelf life and do not get spoiled for months, why?