Question Set A

CBSE 12th Standard Chemistry Amines HOT Questions Study Material - QB365

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Questions:

2 Marks

Complete the following reaction.

How many grams of sucrose (M.wt. = 342) should be dissolved in 100g water in order to produce a solution with 105.0°C difference between the freezing point and the boiling point ?(K_f = 1.86°C/m, K_b = 0.51°C/m)

Outer hard shells oftwo eggs are removed one of the egg is placed in pure water and the other is placed in saturated solution of sodium chloride. What will be observed and why?

Arrange the following in the order of their increasing basicity: p-toluidine, N, N-dimethyl-p-toluidine, p-nitroaniline, aniline

3 Marks

Two isomeric compounds A and B having molecular formula C₄H₁₁N, both lose N₂on treatment with HNO₂ and gives compound C and D respectively. C is resistant to oxidation but immediately responds to Lucas reagent, where as 'D' responds to Lucas reagent after 5 minutes and gives a positive iodoform test. Identify A and B.

Why does bromination of aniline, even under very mild conditions, gives 2, 4, 6-tribromoaniline instantaneously?

A solution containing 15g urea (molar mass = 60 g mol^-1) per litre of solution in water has the same osmotic pressure (isotonic) as a solution of glucose (molar mass = 180 g mol^-1 ) in water. Calculate the mass of glucose present in one litre of its solution.

Explain with example the concept of minimum boiling azeotropes and maximum boiling azeotropes.

When benzene reacts with CH₃CI in presence of AICI₃ to give 'A' (C₇H₈), 'A' reacts with 1 mole of CI₂ in presence of sun light to form 'B' (C₇H₇CI). 'B' on reaction with KC to form 'C'. 'c' on hydrolysis gives 'D'. 'C' on reduction with Na and C₂H₅OH gives 'E'. Identify 'A' to 'E' and explain the reactions.

Multiple Choice Question

10.

An aqueous solution of methanol in water has vapour pressure

(a)

equal to that of water

(b)

equal to that of methanol

(c)

more than that of water

(d)

less than that of water

11.

The values of van't Hoff factors for KCI, NaCI and K₂SO₄, respectively, are ................. .

(a)

2,2 and 2

(b)

2,2 and 3

(c)

1,1, and 2

(d)

1,1 and 1

12.

An ideal solution is formed by mixing two volatile liquids A and B. X_A and X_B are the mole fractions of A and B respectively in the solution and Y_A and Y_B are the are the mole fractions of A and B respectively in the vapour phase. A plot of 1/Y_A along y - axis against 1/X_A along x - axis gives a straight line. What is the slope of the straight line ?

(a)

\({ p }_{ B }^{ o }/{ p }_{ A }^{ o }\)

(b)

\({ p }_{ A }^{ o }/{ p }_{ B }^{ o }\)

(c)

\({ p }_{ B }^{ o }-{ p }_{ A }^{ o }\)

(d)

\({ p }_{ A }^{ o }-{ p }_{ B }^{ o }\)

13.

Benzylamine may be alkylated as shown in the following equation:

C₆H₅CH₂NH₂+R-X \(\longrightarrow \) C₆H₅CH₂NHR

Which of the following alkyl halides is best suited for this reaction through S_N 1 mechanism?

(a)

CH₃Br

(b)

C₆H₅Br

(c)

C₆H₅CH₂Br

(d)

C₂H₅Br

14.

Which gives black precipitate on reaction with CS₂ followed by addition of HgCl₂?

(a)

(CH₃)₃CNH₂

(b)

(C₂H₅)₂NH

(c)

(CH₃)₃N

(d)

all the three

15.

At 40°C the vapour pressure of pure liquids, benzene and toluene, are 160 mmHg and 60 mmHg respectively. At the same temperature, the vapour pressure of an equimolar solution of the two liquids, assuming the ideal solution should be

(a)

140 mmHg

(b)

110 mmHg

(c)

220 mmHg

(d)

100 mmHg

16.

Name the product(s) formed during the reaction of primary aliphatic amines with nitrous acid at room temperature?

(a)

\(\begin{equation} R \mathrm{~N}_{2}^{+} \mathrm{Cl^-} \end{equation}\)

(b)

ROH

(c)

Both (a) and (b)

(d)

None of the above

17.

Which one of the following can be prepared by Gabriel phthalimide synthesis?

(a)

Aniline

(b)

o-Toluidine

(c)

Benzylamine

(d)

N-Methyl ethanamine

18.

Acid anhydrides on reaction with primary amines give ____________

(a)

amide

(b)

imide

(c)

secondary amine

(d)

imine

19.

Which one of the following pairs will not form an ideal solution?

(a)

Benzene and toluene

(b)

n-hexane and n-heptane

(c)

Ethanol and acetone

(d)

Bromoethane and chloroethane

5 Marks

20.

(i) tert-Butylamine cannot be prepared by the action of NH₃ on tert-butyl bromide. Explain why?
(ii) Suggest a convenient method for the preparation of tert-butylamine.

21.

(a) Calculate the freezing point of solution when 1.9 g of MgCI₂ (M = 95 g mol^-1) was dissolved in 50 g of water, assuming MgCI₂ undergoes complete ionization. (K_f for water = 1.86 K kg mol^-1)
(b) (i) Out of 1 M glucose and 2 M glucose, which one has a higher boiling point and why?
(ii) What happens when the external pressure applied becames more than the osmotic pressure of solution?

22.

What is the solubility of a solid in liquid? Describe the various factors on which the solubility of a solid in a liquid depends?

23.

(a) Write the structures of the main products of the following reactions:

(b) Give a simple chemical test to distinguish between Aniline and N,N-dimethylaniline.
(c) Arrange the following in the increasing order of their pK_b values:
C₆H₅NH₂ , C₂H₅NH₂ , C₆H₅NHCH₃

Assertion and reason

24.

In the following questions. an Assertion (A) is followed by a corresponding Reason (R) Use the following keys to choose the appropriate answer.
Assertion (A) Aromatic primary amines cannot be prepared by Gabriel phthalimide synthesis.
Reason (R) Aryl halides do notundergo electrophilic substitution with anion formed by phthalimide.
Codes:
(a) Both (A) and (R) are correct, (R) is the correct explanation of (A).
(b) Both (A) and (R) are correct, (R) is not the correct explanation of (A).
(c) (A) is correct; (R) is incorrect.
(d) (A) is incorrect; (R) is correct.

25.

Assertion: Controlled nitration of aniline at low temperature mainly gives m-nitroaniline.
Reason: In acidic medium, -NH₂ group gets converted into m-directing group.
Codes:
(a) Assertion and reason both are correct statements and reason is correct explanation for assertion.
(b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.
(c) Assertion is correct statement but reason is wrong statement.
(d) Assertion is wrong statement but reason is correct statement.

26.

Assertion : Molarity of a solution in liquid state changes with temperature.
Reason : The volume of a solution changes with change in temperature.
Codes:
(a) If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion.
(b) If both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion.
(c) If the Assertion is correct but Reason is incorrect.
(d) If both the Assertion and Reason are incorrect.

27.

Assertion: A solution is a homogeneous mixture of two or more chemically non-reacting substances.
Reason: Solutions can be made between any two states of matter.
Codes:
A) Assertion and reason both are correct statements and reason is correct explanation for assertion.
B) Assertion and reason both are correct statements but reason is not correct explanation for assertion.
C) Assertion is correct statement but reason is wrong statement.
D) Assertion is wrong statement but reason is correct statement.

Case Study Questions

28.

Organic compounds containing amine as functional group are present in wide variety of compounds namely amino acids, hormones, neurotransmitters, DNA, alkaloids, dyes etc. Drugs including nicotine, morphine, codein, heroin etc. which have physiological effects on human also contain -NH₂ group in one form or another. Amines are basic in nature due to presence of lone pair of electron on nitrogen. Adrenaline hormone and ephedrine drug, both contain second amino group are used for increasing blood pressure. Novacain, a synthetic compound contains both primary ana tertiary amino group, is used as anaesthetic in dentistry. Benadryl, a widely used antihistamine drug contains tertiary amino group, Quarternary ammonium salts of long chain, tertiary amines are used as cationic detergents. Diazonium salts are used for synthesis of azodyes and useful aromatic compounds.
(a) Write the formula of tertiary amine with molecular formula C₃H₉N, which does not react with Hinsberg reagent?
(b) Convert Aniline to p-hydroxy azo benzene.
(c) Give one example of cationic detergent.
(d) What is formula of paracetamol, (crosin), a well known antipyretic?
(e) How will you distinguish between Aniline and Benzyl amine?

29.

The concentration of a solute is very important in studying chemical reactions because it determines how often molecules collide in solution and thus indirectly determines the rate of reactions and the conditions at equilibrium. There are several ways to express the amount of solute present in a solution. The concentration of a solution is a measure of the amount of solute that has been dissolved in a given amount of solvent or solution. Concentration can be expressed in terms of molarity, molality, parts per million, mass percentage, volume percentage, etc.
(i) The molarity (in mol L^-1) of the given solution will be
(a) 1.56
(b) 1.89
(c) 0.263
(d) 1.44
(ii) Which of the following is temperature dependent?
(a) Molarity
(b) Molality
(c) Mole fraction
(d) Mass percentage
(iii) Which of the following is true for an aqueous solution of the solute in terms of concentration?
(a) 1 M = 1 m
(b) 1M > 1m
(c) 1M < 1 m
(d) Cannot be predicted

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Answers Key:

2 Marks

72 g

The egg placed in pure water will swell because the concentration of proteins is high inside the egg as compared to water. Therefore water diffuses through the semi- permeable membrane of egg and egg swells.
On the other hand the egg placed in sodium chloride solution will shrink due to osmosis, water will move out of the egg membrane. thereby, shrinking the egg.

p-nitroanlline < aniline < p-toluidine < N,N-dimethyl p-toluidine.

3 Marks

Due to strong electron-donating effect of the -NH₂ group, the electron density increases at the 0-, positions. Further, when aniline is treated with Br₂ the Br⁺ attacks the benzene ring at o- and p-positions to form carbocation intermediates which are stabilized not only by the usual resonance of the Henzene ring. but also by the -NH₂ group as shown below: In case of o-bromination, the carbocation intermediate is stabilized not only by usual resonating structure (I, III and IV) but is also stabilized by resonance structure (II) in which the lone pair of electrons on the N. atom interacts with the positively charged carbon of the ring. Similarly, in case of p-bromination, the carbocation is stabilized not only by the usual resonating structures (V, VI, and VIII) but is also stabilized by the resonance structure (VII) in which the lone pair of electrons on the N-atom interacts with the positively charged carbon of the ring. These additional resonating structures (II and VII) increase the stability of the carbocation to such an extent that bromination occurs instantaneously at the p- and two. o- positions giving 2, 4, 6-tribromoaniline.

Here,
\( Here, W_{1}=15 \mathrm{~g}, M_{1}=60 \mathrm{~g} \mathrm{~mol}^{-1}, V_{1}=1 \mathrm{~L}\)
\(M_{2}=180 \mathrm{~g} \mathrm{~mol}^{-1}, V_{2}=1 \mathrm{~L}\)
\(\pi=C R T=\frac{W}{m} \frac{R T}{V} \)
For both solutions, \(\pi\), R, T and V are same.
For urea solution, \(\pi=\frac{15 R T}{60}\)
For glucose solution,\(\pi=\frac{W_{2} R T}{180}\)
\(\because\frac{15 R T}{60} =\frac{W_{2} R T}{180} \)
\(\therefore W_{2} =\frac{15 \times 180}{60}=45 \mathrm{~g}\)

Maximum boiling azeotropes
Maximum boiling azeotropes are those which boil at a higher temperature than the boiling point of each component in a pure state,
e.g., 68 % nitric acid and 32 % water by mass.
Minimum boiling azeotropes
Minimum boiling azeotropes are those which boil at a lower temperature than boiling point of each component in the pure state,
e.g., 95.5 % ethyl alcohol and 4.5 % water by mass.

Multiple Choice Question

10.

Methanol being more volatile than water, the solution of methanol in water will have more vapour pressure than water (a case of positive deviation).

11.

(b)
2,2 and 3

12.

(a)
\({ p }_{ B }^{ o }/{ p }_{ A }^{ o }\)

13.

Since C₆H₅CH₂Br on ionization gives a resonance stabilized benzyl carbocation \(\left( { C }_{ 6 }{ H }_{ 5 }{ CH }_{ 2 }^{ + } \right) \) , therefore, C₆H₅CH₂Br is best suited for S_N1 reaction.

14.

Only \({ 1 }^{ \circ }\) amines undergo Hofmann Mustard oil reaction and thus give a black ppt. of HgS.

15.

(b)
110 mmHg

16.

(b)
ROH

17.

18.

(a)
amide

19.

5 Marks

20.

(i) tert-Butyl bromide being a 3° alkyl halide on treatment with a base (i.e. NH₃) prefers to undergo elimination rather than substitution. Therefore, the product is isobutylene rather than tert-butylamine.

1° amines containing tert-alkyl groups can be prepared by action of suitable Grignard reagents on O-methylhydroxylarnine. For example,

21.

(a) \(\Delta { T }_{ f }=i\frac { { K }_{ f }{ W }_{ b }\times 1000 }{ { M }_{ b }\times { W }_{ a } } \)
\(\Delta { T }_{ f }=3\times \left( \frac { 1.86\times 1.9 }{ 95\times 50 } \right) \times 1000\)
= 2.23 K
\(\Delta { T }_{ f }-{ \Delta T }_{ f }^{ ' }=\frac { 273.15-2.23 }{ 273-2.23 } \)
\({ T }_{ f }^{ ' }\) = 270.92 K or 270.77 K
(b) (i) 2 M glucose has a higher boiling point because higher the number of particles lesser is the vapour pressure.
(ii) Reverse osmosis.

22.

Solubility of Solids In Liquids:
Solubility is the interaction between particles of the solute and the solvent. Hence, it depends on the nature of the solute and the solvent, as well as on the temperature and pressure. But the solubility of solids in liquids is independent of pressure.
Factors affecting solubility
1. Temperature. Basically, solubility increases with temperature.
2. Polarity. In most cases solutes dissolve in solvents that have a similar polarity.
3. Pressure. Solid and liquid solutes.
4. Molecular size.
5. Stirring increases the speed of dissolving.

23.

(b) Carbylamine test: Add CHCl₃and KOH to each of them, aniline will give offensive smelling compound whereas N, N-Dimethyl aniline will not react
(c) C₂H₅NH₂ < C₆H₅NHCH₃ < C₆H₅NH₂ is increasing order of their pKb due to decreasing order of basic character.

Assertion and reason

24.

(c) Aromatic primary amines cannot be prepared by the Gabriel phthalimide synthesis because aryl halides do not undergo nucleophilic substitution reaction with the anion formed by phthalimide. Thus, (A) is correct but (R) is incorrect

25.

(a): Under acidic condition, aniline gets protonated to anilinium ion (-NH₃⁺ group). This is deactivating and m-directing group. Thus, controlled nitration of aniline mainly gives m-nitroaniline.

26.

(a) If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion.

27.

B) Assertion and reason both are correct statements but reason is not correct explanation for assertion.
Explanation:
A homogeneous mixture consists of a single phase which has properties that may differ from those of the individual components i.e., solute and solvent.

Case Study Questions

28.

(a) (CH₃)₃N does not react with Hinsberg reagent.
(b)

(c)
cetyltrimethyl ammonium bromide.
(d)

(e) Add NaNO₂ and cone, HCI. Cool it to 0 - 5°C. Then add alkaline solution of phenol. Aniline will give orange, azo dye, whereas Benzyl amine does not.