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Aliphatic Amines - ISC Class 12 Chemistry Questions with Answers, Page 3

45 past-paper questions on Aliphatic Amines from ISC Class 12 Chemistry papers (2027-2018), newest first, in full. Questions 41-45 are on this page, 20 to a page. Tap "Show answer" under a question to see its answer.

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2020 · 2 marks · Short answerOpen: State reasons for the following: Ethylamine is soluble in water whereas aniline…

Answer the following.

State reasons for the following:
(i)[1.0]
Ethylamine is soluble in water whereas aniline is insoluble in water.
(ii)[1.0]
Aliphatic amines are stronger bases than aromatic amines.
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Answer (i)

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Because ethylamine forms hydrogen bonds with water molecules, whereas in aniline the large hydrophobic $\mathrm{C_6H_5}$ group reduces solubility in water.

Answer (ii)

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Because in aliphatic amines the alkyl group (+I effect) increases electron density on nitrogen, whereas in aromatic amines the lone pair on nitrogen is delocalised into the benzene ring (resonance), making it less available for donation.
2018 · 1 mark · ArrangeOpen: Decreasing order of basic strength in gas phase: , , and .

Arrange the following in the order asked.

Decreasing order of basic strength in gas phase: $\text{C}_2\text{H}_5\text{NH}_2$, $(\text{C}_2\text{H}_5)_2\text{NH}$, $(\text{C}_2\text{H}_5)_3\text{N}$ and $\text{NH}_3$.
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Answer

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Order, first to last: (C2H5)3N, (C2H5)2NH, C2H5NH2, NH3

$(\mathrm{C_2H_5})_3\mathrm{N} > (\mathrm{C_2H_5})_2\mathrm{NH} > \mathrm{C_2H_5NH_2} > \mathrm{NH_3}$ Because in the gas phase only the +I effect operates, so basic strength rises with the number of alkyl groups.
2018 · 1 mark · ArrangeOpen: Arrange the following in the increasing order of their basic strength: , ,

Arrange the following in the order asked.

Arrange the following in the increasing order of their basic strength: $\text{C}_2\text{H}_5\text{NH}_2$, $\text{C}_6\text{H}_5\text{NH}_2$, $(\text{C}_2\text{H}_5)_2\text{NH}$
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Answer

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Order, first to last: C6H5NH2, C2H5NH2, (C2H5)2NH

$\mathrm{C_6H_5NH_2} < \mathrm{C_2H_5NH_2} < (\mathrm{C_2H_5})_2\mathrm{NH}$
2018 · 2 marks · IdentifyOpen: Identify the compounds A, B, C and D.

Answer the following.

Identify the compounds A, B, C and D. $\text{CH}_3\text{CN} \xrightarrow{\text{H}_2\text{O}/\text{H}^+} \text{A} \xrightarrow{\text{NH}_3} \text{B} \xrightarrow{\text{heat}} \text{C} \xrightarrow{\text{Br}_2/\text{KOH}} \text{D}$
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Answer

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A - ethanoic acid: CH3COOH

B - ammonium ethanoate: CH3COONH4

C - ethanamide: CH3CONH2

D - methanamine: CH3NH2

A = ethanoic acid ($\mathrm{CH_3COOH}$) B = ammonium ethanoate ($\mathrm{CH_3COONH_4}$) C = ethanamide ($\mathrm{CH_3CONH_2}$) D = methanamine ($\mathrm{CH_3NH_2}$)
2018 · 1 mark · ArrangeOpen: Increasing order of solubility in water: , , .

Arrange the following in the order asked.

Increasing order of solubility in water: $\text{C}_6\text{H}_5\text{NH}_2$, $(\text{C}_2\text{H}_5)_2\text{NH}$, $\text{C}_2\text{H}_5\text{NH}_2$.
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Answer

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Order, first to last: C6H5NH2, (C2H5)2NH, C2H5NH2

$\mathrm{C_6H_5NH_2} < (\mathrm{C_2H_5})_2\mathrm{NH} < \mathrm{C_2H_5NH_2}$ Because the large hydrophobic phenyl group reduces hydrogen bonding most, and the primary amine with two N-H bonds forms more hydrogen bonds with water than the secondary amine.

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