2 Marks Questions

Question 12 Marks

Compound (A) is formed when aniline is treated with $NaNO _2+ HCl$ at 273-278 K. Compound (B) is formed when cuprous chloride is added to (A).
Write the name of compound (A) and (B) and the equations of the chemical reactions involved.

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Question 22 Marks

Compound (A) is formed when benzene diazonium chloride is mixed with KI solution. Compound (B) is formed when ( A ) reacts with sodium in the presence of dry ether. Write the names of (A) and (B) and the equations of the chemical reactions involved.

Answer

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Question 32 Marks

Explain isocyanide test for primary amines.

Answer

When aliphatic and aromatic primary amine, is heated with chloroform and alcoholic (ethanolic) KOH, it forms foul smelling substance carbylamine or isocyanide. This is called isocyanide test.
Secondary and tertiary amines do not give this test.Therefore, this reaction is used in testing primary amines.

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Question 42 Marks

Draw the pyramidal shape of trimethyl amine.

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Question 52 Marks

How will you make the following changes?
(i) Methyl alcohol to ethyl amine.
(ii) Ethanoic acid to ethanamine.

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Question 62 Marks

Ethyl amine is basic while acetamide is ampheteric. Explain the reason.

Answer

In ethylamine, the lone electron pair of Nitrogen of$-NH_2$ group is easily available to accept proton. Whereas in acetamide due to the presence of

group and its $-I$ effect the lone electron pair of $-NH_2$ group is involved in resonance hence, it is not readily available to accept proton. There by, ethyl amine is basic whereas acetamide is amphoteric in nature.

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Question 72 Marks

Of all the methods of preparing amines identify by which aniline cannot be prepared?

Answer

Aniline cannot be prepared by the following methods:
(i) Reduction of nitriles
(ii) Reduction of amides
(iii) Reduction of oximes
(iv) Reductive amination of carbonyl compounds.

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Question 82 Marks

Write the reaction sequence required to prepare 2-Bromo-4-methyl aniline from p-amino toluene.

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Question 92 Marks

(i) Name the product obtained when excess of ethanol is treated with ammonia in the presence of Alumina?
(ii) How is methyl amine prepared from the following compounds? Give the equation.
(a) $CH _3- MgCl$
(b) $CH _3 COCl$

Answer

(i) When excess of ethanol is treated with ammonia in the presence of alumina, a mixture of primary, secondary and tertiary amines is obtained

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Question 102 Marks

Complete the following reactions:

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Question 112 Marks

How is $p-$nitroaniline is prepared by nitration of aniline? Explain with equations.

Answer

Due to the oxidising properties of conc. $HNO_3$ present in the nitration mixture, it oxidises aniline.
Therefore, to control this reaction, the $-NH_2$ group is protected by acetylation of aniline before nitration.

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Question 122 Marks

Two isomeric compounds $(A$ and $B)$ have $\ce{ C_4H_{11}N}$ molecular formula react with $\ce{HNO_2}$ and forms compounds $(C)$ and $(D). C$ is hardly oxidised but it reacts immediately with Lucas reagent whereas $D$ reacts with Lucas reagent in $5$ minutes and it also gives haloform reaction. Identify $\ce{A, B, C}$ and $\ce{D}$.

Answer

$A$ and $B$ are primary amines, which react $\ce{HNO_2}$ and forms corresponding alcohols, $C$ is a tertiary alcohol which is hardly oxidised and it reacts immediately with Lucas reagent and $D$ is a secondary alcohols,
hence it reacts with Lucas reagent in $5$ minutes and due to

group it gives haloform reaction.

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Question 132 Marks

Write short notes :
Diazotisation

Answer

Diazotisation : When aromatic amine is treated with $NaNO _2$ and $HCl (273-278 K)$ arene diazonium salts are formed. This reaction is called diazotisation. By the reaction of aniline benzene diazonium chloride is formed. Due its instability this is used immediately.

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Question 142 Marks

Write short notes :
Carbylamine reaction

Answer

Carbyl amine reaction : Aliphatic and aromatic primary amine are heated with chloroform and ethanolic potassium hydroxide then pungent smelling substance isocyanide or carbyl amine is formed. This reaction is not shown by secondary and tertiary amines.

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Question 152 Marks

Account for the following :
Although amino group is $o-$ and $p$ - directing in aromatic electrophilic substitution reacts, aniline on nitration gives a substantial amount of m-nitro aniline.

Answer

Amino group is ortho and para directing for electrophilic substitution reaction but in the nitration of aniline substantial amount of meta nitro aniline is formed, because in strong acidic medium aniline accepts proton and forms anilium ion which is meta directing (due to - I effect). In this reaction $51 \%$ para and $2 \%$ ortho products are also formed.

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Question 162 Marks

Account for the following :
Methyl amine in water reacts with ferric chloride to precipitate hydrated ferric oxide.

Answer

Methyl amine gives $\overline{ O } H$ ion in aqueous solution which reacts with $FeCl _3$ (aqueous) first gives hydroxide and then precipitate of hydrated oxide. Reactions are as under :

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Question 172 Marks

Account for the following :
$pK _{ b }$ of aniline is more than that of methyl amine.

Answer

In methyl amine due to + I effect (electron repelling effect) of methyl group electron density on nitrogen atom increases so electron donating tendency of this also increases so basic character of this is morewhile in aniline

lone pair of electron on nitrogen participates with resonance with benzene ring ( + M effect) so electron density on nitrogen decreases so electron donating tendency of this decreases so basic character of this is less. Due to this reason $pK _{ b }$ of aniline is less than methyl amine becasue basic character $\propto \frac{1}{ pK _{ b }} \propto K _{ b }$ (Base dissociation constant).

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Question 182 Marks

Give plausible explanation of :
Why are aliphatic amines stronger bases than aromatic amines?

Answer

ln aliphatic amines due to $+I$ effect (electron repelling effect) electron density on nitrogen increases so electron pair donating tendency of $- NH _2$ group also increases so more are these basic while in aromatic amines lone pair of electron of nitrogen of $- NH _2$ participates in resonance with benzene ring ( + M effect) so electron density on this decreases hence electron donating tendency also decreases, so these are less basic.

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Question 192 Marks

Give plausible explanation of :
Why do primary amines have higher boiling point than tertiary amines?

Answer

Primary amines have two hydrogen atoms on nitrogen so these have strong intermolecular hydrogen bond due to which molecular association is move while in tertiary main hydrogen bond is not formed due to absence of hydrogen atom on nitrogen. So primary amines have higher boiling point than tertiary amines.

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Question 202 Marks

Write the reaction of (i) aromatic and (ii) aliphatic primary amines with nitrous acid.

Answer

Aliphatic primary amine gives mainly alcohol by the reaction with nitrous acid.
$RNH _2+ HNO _2 \xrightarrow[0^{\circ} C ]{ NaNO _2+ HCl } R - OH + N _2+ HO _2$
Aromatic amines forms diazonium salts by the reaction with nitrous acid $\left( NaNO _2+ HCl \right)$.

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Chemistry 2 Marks Questions

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