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Give reasons for the following : a. Sodium metal can be used for drying diethyl ether but not ethanol. b. phenol is an acid but it does not react with sodium bicarbonate. c. Acid catalyzed dehydration of t-butanol is faster than that of n -butanol.

Give reasons for the following :
a. Sodium metal can be used for drying diethyl ether but not ethanol.
b. phenol is an acid but it does not react with sodium bicarbonate.
c. Acid catalyzed dehydration of t-butanol is faster than that of n-butanol.

Grade:12th pass

1 Answers

Kevin Nash
askIITians Faculty 332 Points
10 years ago

(i) Ethanol (due to the presence of active hydrogen atom, C base 2H base 5 – O - H) reacts with sodium metal, while ether and benzene have no such hydrogen atom and hence do not react with sodium and thus can be dried by metallic sodium.

(ii) phenol (a weaker acid) reacts with NaHCO base 3 (a weaker base) to form phenoxide ion (a stronger base) and carbonic acid (a stronger acid).

C base 6H base 5OH + NaHCO base 3 ? C base 6H base 5ONa + H base 2CO base 3

Weaker acid weaker base Stronger base Stronger acid

Since acid-base equilibria lie towards the weaker acid and weaker base, phenol does not decompose NaHCO base 3 (difference from carboxylic acids).

RCOOH + NaHCO ? RCOONa + H base 2CO base 3

Stronger acid Stronger base Weaker base Weaker acid

(iii)Since 3° carbocation (formed in case of t-butanol) is more stable than 1° (formed in case n-butanol), the dehydration in the former proceeds faster than in the latter.

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