CBSE Class 12 Chemistry 2023 Delhi Set 1 Solved Paper

Question : 34

Total: 35

(a) (i) Write the reaction involved in Cannizaro's reaction.
(ii) Why are the boiling point of aldehydes and ketones lower than that of corresponding carboxylic acids?
(iii) An organic compound 'A' with molecular formula C5H8O2 is reduced to n-pentane with hydrazone followed by heating with NaOH and Glycol. 'A' forms a dioxime with hydroxylamine and gives a positive Iodoform and Tollen's test. Identify ' A ' and give its reaction for Iodoform and Tollen's test.
OR
(b) (i) Give a chemical test to distinguish between ethanol acid and ethanoic acid.
(ii) Why is the α-hydrogens of aldehydes and ketones are acidic in nature?
(iii) An organic compound ' A ' with molecular formula C4H8O2 undergoes acid hydrolysis to form two compounds ' B ' and ' C '. Oxidation of ' C ' with acidified potassium permanganate also produces 'B'. Sodium salt of 'B' on heating with soda lime gives methane.
(1) Identify ' A ', ' B ' and ' C '.
(2) Out of 'B' and ' C ', which will have higher boiling point? Give reason.

Solution: 👈: Video Solution

Cannizaro Reaction (a) (i)

(ii) Boiling points of aldehyde and ketones are less than carboxylic acid because carboxylic acid have hydrogen bonding and associated molecules bonding which increases the boiling point of carboxylic acids.
(iii)

(b) (i) Sodium bicarbonate (NaHCO3) is used to distinguish ethanol and ethanoic acid ethanoic acid give brick Red fumes with sodium bicarbonate.
ethanol do not react with sodium bicarbonate.
(ii) α-Hydrogen is always attached with oxygen which is highly electronegative and having lone pair of electrons. Alpha hydrogen atom when donate electron it act as an acid.

CH3−COO−C2H5

(A)

H2O∕H+

────▸

CH3−COOH

(B)

C2H5−OH

(C)

C2H5−OH+[O]

KMnO4

─────▸

CH3−COOH

(B)

CH3−COONa

(Salt‌of‌B)‌sodiumacetate

──────▸

CaO+NaOH

soda‌lime

CH4+Na2CO3

methane

1. A- CH3−COOC2H5 (ethyl methanoate)
B−CH3−COOH (ethanoic acid)
C−CH3−COONa (sodium acetate)
2. Ethanoic acid will have higher boiling point because it contain associate molecule which participate in hydrogen bonding. H-bonding is strong bonding which required high temperature to boil.

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