CBSE Class 12 Chemistry Amines Questions

Question. Which of the following is formed when an alkyl primary amine reacts with nitrous acid?
a. Alkyl nitrite
b. Secondary amine
c. Nitroalkane
d. Alcohol
Answer. D

Question. Arrange the following compounds in increasing order of basicity: CH₃NH₂, (CH₃)₂ NH, NH₃, C₆H₅NH₂ in aqueousmedium
a. C₆H₅NH₂ < NH₃ < (CH₃)₂NH < CH₃NH₂
b. CH₃NH₂ < (CH₃)₂NH < NH₃ < C₆H₅NH₂
c. C₆H₅NH₂ <NH₃ < CH₃NH₂<(CH₃)₂NH
d. (CH₃)₂NH < NH₃ < C₆H₅NH₂ < CH₃NH₂
Answer. C

Question. Reduction of CH₃CH₂NC with hydrogen in presence of Ni or Pt as catalvst gives
a. CH₃CH₂NH₂
b. CH₃CH₂NHCH₃
c. CH₃CH₂NHCH₂CH₃
d. (CH₃)₃N
Answer. B

Question. When hypophosphorous acid is treated with diazonium salts, it is reduced to which of the following compound?
a. Arene
b. Methane
c. Ethyl alcohol
d. Amines
Answer. A

Question. The correct IUPAC name for CH₂ = CHCH₂NHCH₃ is
a. Allylmethylamine
b. 2-amino-4-pentene
c. 4-aminopent-1-ene
d. N-methylprop-2-en-1-amine
Answer. D

Question. C₃H₈N cannot represent
a. 1° ammine
b. 2° ammine
c. 3° ammine
d. Quartemary ammonium salt
Answer. D

ASSERTION -REASON TYPE QUESTIONS

Choose the correct answer from the following choices
a Both assertion and reason are correct statements and reason is correct explanation of assertion
b Both assertion and reason are correct statements but reason is not correct explanation of assertion
c Assertion is correct statement but reason is wrong statement
d Assertion is wrong statement but reason is correct statement

Question.6 Assertion: Aniline reacts with bromine water to form 2,4,6-tribromoaniline
Reason: Aniline is resonance stabilized
Answer. B

Question. Assertion: Acetanilide is less basic than aniline
Reason: Acetylation of aniline results in decrease of electron density on nitrogen
Answer. A

Question. Assertion: The order of basicity of amines in gaseous state is different than those in aqueous solution
Reason: In aqueous solution solvation is also to be takes in to account.
Answer. A

Question. Assertion: Only a small amount of HCl is required to initiate the reduction of Nitro compounds with iron scrap and HCl
Reason: FeCl₂ formed gets hydrolysed to release HCl during the reaction.
Answer. A

Question. Assertion: Hinsberg’s reagent does not react with tertiary amines
Reason: No hydrogen atom is attached to nitrogen of amino group.
Answer. A

Question. Assertion: N,N diethyl benzene sulphonamide is insoluble in alkali.
Reason: Sulponyl group attached to nitrogen is strong electron withdrawing group
Answer. A

Question. Assertion: Amides on oxidation yields amines
Reason: Amides on treating with lithiumaluminiumhydride gives amines
Answer. D

CASE BASED QUESTIONS

1.Basicity of aliphatic amines in aqueous solution depends on +I effect, extent of hydrogen bonding with water molecules, steric effects of the alkyl group. In aromatic amines it depends on effect of substituents on the ring. Basicity of aralkyl amines, as the electrons are not conjugated with benzene ring and not de- localized. Hence electron pair is available for protonation. In aromatic amines ortho effect refers mainly to the set of steric effects and some bonding interactions along with polar effects caused by the various substituents which are in a given molecule altering its chemical properties and physical properties. In a general sense the ortho effect is associated with substituted benzene compounds.
Anything ortho to the amine, no matter whether it is electron donating or withdrawing, will decrease the basicity of the aromatic amine. This is because of the ortho effect, which is basically steric effect. The protonated amine will have a greater steric interaction with the ortho group, so it will be less stable.

Question. Compare the basicity of aniline, m-nitroaniline, p- nitroaniline and ortho nitroaniline
Answer. o-nitroaniline<p-nitroaniline<m-nitroaniline<Aniline(ewg decreases the basicity due to ortho effect o-nitro aniline is the weak one among substituted anilines)

Question. Compare the basicity of benzylamine, aniline, methyl amine and ammonia
Answer. aniline<ammonia<benzylamine<methyl amine (methyl group is more electron donating than benzyl group, hence methyl amine is stronger base, in benzyl amine electrons are not delocalised. Hence better base than aniline but ammonia with pKb value4.75 is more basic than benzylamine(pKb=4.70)

Question. Aniline has pKb =9.38,p-aminophenol has pKb =8.50 and o-aminophenol has pKb=9.28, but m-aminophenol has pKb=9.80. Explain.
Answer. Here though -OH group is in ortho position o-aminophenol is stronger base than aniline (pkb=9.38) and m-aminophenol(pKb=9.80) due to stabilisation of anilinium ion by hydrogen bonding.

2. Amines have higher boiling points than hydrocarbons of comparable molecular weight because the C—N bond is more polar than a C—C bond. Also, primary and secondary amines can form intermolecular hydrogen bonds because they can act as both hydrogen bond donors and acceptors. Tertiary amines have no hydrogen atoms bonded to the nitrogen atom and therefore are not hydrogen bond donors.
Thus, tertiary amines cannot form intermolecular hydrogen bonds. As a result, they have lower boiling points than primary and secondary amines of comparable molecular weight. Amines have lower boiling points than alcohols because nitrogen is less electronegative than oxygen. As a result the N—H bond is less polar than the O—H bond, and the hydrogen bond in amines is weaker than the hydrogen bond in alcohols.

Question. The boiling point of Ethyl alcohol is more than that of ethyl amine. Give reason
Answer. N is less electronegative than oxygen and the hydrogen bond in amines are weaker than that in alcohols.

Question. The order of boiling points for the following amines is CH₃CH₂CH₂NH₂> (CH₃CH₂CH₂) NH>(CH₃CH₂) N(CH₃),Explain
Answer. The boiling points of amines follows the order primary>secondary>tertiary Primary amines have 2 ,secondary amines have 1 while tertiary amines have no hydrogen linked to nitrogen.
Among these compounds of comparable molecular masses ,order of extend of hydrogen bond is hydrocarbons <amines<alcohols<carboxylic acids

Question. Arrange the following in the increasing order of molecular mass. CH₂CH₂NH₂,HCOOH,CH₃CH₂OH,CH₃CH₂CH₃
Answer. Hence the order of given compounds of comparable molecular masses is CH₃CH₂CH₃< CH₂CH₂NH₂< CH₃CH₂OH< HCOOH

SHORT ANSWER TYPE QUESTIONS:

Question. Why aniline does not undergo Friedel -Crafts reaction?
Answer. Aniline does not undergo Friedel-Crafts reaction due to salt formation with aluminum chloride, the Lewis acid, which is used as a catalyst.

Question. Why cannot aromatic primary amines be prepared by Gabriel phthalimide synthesis?
Answer. Aromatic primary amines cannot be prepared by this method because aryl halides do not undergo nucleophilic substitution with the anion formed by the phthalimide.

Question. Why do primary amines have higher boiling point than tertiary amines?
Answer. Primary amines are associated with inter molecular hydrogen bonding while tertiary amines does not.

Question.Why are aliphatic amines stronger bases than aromatic amines?
Answer. In aliphatic amines alkyl group increases the electron density on N of –NH2 group while in aromatic amines lone pair on N is not available for donation since it is involved in conjugation with pi electrons of benzene ring.

Question. Why are amines less acidic than alcohols of comparable molecular masses?
Answer. Amines are having –NH2 group which donates lone pair of electron hence basic. Alcohols can provide hydronium ions hence highly acidic in nature.

Question. Give reasons for the following:
Primary amines have higher boiling point than tertiary amines. 
Answer. Primary amines (R – NH2) have two hydrogen atoms on nitrogen which can undergo intermolecular hydrogen bonding whereas no such hydrogen bonding is present in tertiary amines (R3N). So, primary amines boil at a higher temperature than tertiary amines.

Question. Arrange the following in the increasing order of their boiling point:
2H₅NH₂, C₂H₅OH, (CH₃)₃N
Answer. Increasing order of boiling points : (CH₃)₃N < C₂H₅NH₂ < C₂H₅OH
Tertiary amine does not have hydrogen to form hydrogen bonding and hydrogen bonding in alcohol is stronger than that of amines because oxygen is more electronegative than nitrogen.