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Methods of purification of organic compounds - class-XI

Description: methods of purification of organic compounds
Number of Questions: 20
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Tags: chemistry organic chemistry - some basic principles and techniques organic chemistry : some basic principles and techniques
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Which one of the following reagent is useful for separating aniline from nitrobenzene?

methods of purification of organic compounds methods of purification - organic compounds organic chemistry - some basic principles and techniques organic chemistry : some basic principles and techniques chemistry biochemical techniques

  1. $ aq. NaHCO _3 $

  2. $ aq. NaHSO _3 $

  3. $ aq. HCl $

  4. $dil. H _2SO _4 $

Show answer
Correct Option: C
Explanation:

The reagent selected should be such that only one of components to be separated, reacts with it.


Aniline $+$ aq, HCl $\rightarrow$ salt, which is soluble in water
Nitrobenzene $+$ aq. HCl$\rightarrow$ no reaction.

Therefore, aq. HCL is used to separate aniline and nitrobenzene.

 A mixture of two immiscible liquids chlorobenzene and water boils at $90^{0}C$ and an external pressure of 740.2 torr. If vapour pressure of pure water at $90^{0}C$ is 530 torr then the mole % of chlorobenzene in the distillate will be:

methods of purification of organic compounds methods of purification - organic compounds organic chemistry - some basic principles and techniques organic chemistry : some basic principles and techniques chemistry biochemical techniques

  1. 80%

  2. 40%

  3. 28%

  4. 60%

Show answer
Correct Option: C

Mixed melting point is determined to check.

methods of purification of organic compounds methods of purification - organic compounds organic chemistry - some basic principles and techniques organic chemistry : some basic principles and techniques chemistry biochemical techniques

  1. The purity of organic compound

  2. Whether the two compounds are same

  3. Whether the two compounds are different

  4. Whether the two compounds can be separated by fractional crystallisation method

Show answer
Correct Option: A,B,C

Match the following:

(A) Sublimation (i) Ether $+$ toluene
(B) Distillation (ii) o-Nitrophenol $+$ p-nitrophenol
(C) Vacuum distillation (iii) Benzoic acid $+$ benzaldehyde
(D) Steam distillation (iv) Glycerol from spent lye
methods of purification of organic compounds methods of purification - organic compounds organic chemistry - some basic principles and techniques organic chemistry : some basic principles and techniques chemistry biochemical techniques

  1. (A)-(iv), (B)-(iii), (C)-(ii), (D)-(i)

  2. (A)-(i), (B)-(ii), (C)-(iii), (D)-(iv)

  3. (A)-(iii), (B)-(i), (C)-(iv), (D)-(ii)

  4. (A)-(ii), (B)-(iv), (C)-(i), (D)-(iii)

Show answer
Correct Option: C

Compare List I and List II and choose the correct matching codes from the choices given.


List I List II
(A) Glycerol (i) Sublimation
(B) o-nitrophenol (ii) Beilstein's test
(C) Anthracene (iii) Victor-Meyer's method
(D) Halogens (iv) Steam distillation
(E) Molecular weight (v) Vacuum distillation
(vi) Eudiometry


methods of purification of organic compounds methods of purification - organic compounds organic chemistry - some basic principles and techniques organic chemistry : some basic principles and techniques chemistry biochemical techniques

  1. (A-v), (B-iv), (C-i), (D-ii), (E-iii)

  2. (A-iv), (B-v), (C-i), (D-vi), (E-ii)

  3. (A-vi), (B-iv), (C-i), (D-iii), (E-ii)

  4. (A-v), (B-iv), (C-vi), (D-ii), (E-iii)

  5. (A-iv), (B-vi), (C-ii), (D-iii), (E-v)

Show answer
Correct Option: A
Explanation:
  • Sublimation-Conversion of solid directly into gaseous phase. The liquid state does not exist. e.g., naphthalene, anthracene. 
  • Beilstein test-Simple chemical test for halogens. 
  • Victor-Meyers method-Standard laboratory method for determining the molecular weight of a volatile liquid. 
  • Steam distillation- Vaporization of the volatile constituents of a liquid. It is special type of distillation for temperature-sensitive materials like aromatic natural compounds, eg,-ortho nitrophenol, cinnamaldehyde. 
  • Vacuum distillation-Distillation at reduced pressure. It is generally used in case of high boiling liquids which decompose below their normal boiling points, cant be purified by distillation at atmospheric pressure.
  • Eudiometry-It is the process of determining the constituents of a gaseous mixture by eudiometer. It is used for ascertaining the purity of air or amount of $O _2$ in it.

Mixture of benzene and aniline can be separated by?

methods of purification of organic compounds methods of purification - organic compounds organic chemistry - some basic principles and techniques organic chemistry : some basic principles and techniques chemistry biochemical techniques

  1. Distillation

  2. Steam distillation

  3. dil. HCl

  4. di. NaOH

Show answer
Correct Option: A,C

Which method cannot be used for purification
of liquids?

methods of purification of organic compounds methods of purification - organic compounds organic chemistry - some basic principles and techniques organic chemistry : some basic principles and techniques chemistry biochemical techniques

  1. Chromatographic

  2. Steam distillation

  3. Sublimation

  4. Distillation

Show answer
Correct Option: C
Explanation:

Sublimation is the process in which solid changes directly to vapour state without passing through the liquid state.So sublimation cannot be used for purification of liquids.

Choose the correct option for the two statements given below :
Statement I: Sharp melting point can be used to test the purity of the compound.
Statement II: Impurities cause a decrease in the melting point of the compound.

methods of purification of organic compounds methods of purification - organic compounds organic chemistry - some basic principles and techniques organic chemistry : some basic principles and techniques chemistry biochemical techniques

  1. Both statements I and II are correct.

  2. Both statements I and II are incorrect.

  3. Statement I is correct and statement II is incorrect.

  4. Statement I is incorrect and statement II is correct.

Show answer
Correct Option: A
Explanation:

The purity of an organic compound can be tested by its sharp melting point. The impurities present in the compound can cause a decrease in melting point.


The presence of even a small amount of impurity will lower a compound's melting point by a few degrees and broaden the melting point temperature range.

Option A is correct.

Assertion (A): Components of rectified spirit
cannot be separated by distillation
Reason (R): Rectified spirit is an Azeotropic
mixture

methods of purification of organic compounds methods of purification - organic compounds organic chemistry - some basic principles and techniques organic chemistry : some basic principles and techniques chemistry biochemical techniques

  1. Both A and R are true and R is correct explanation of A

  2. Both A and R are true and R is not correct explanation of A

  3. A is true but R is false

  4. A is false but R is true

Show answer
Correct Option: A
Explanation:

An azeotropic is a mixture of 2 or more liquids in such a way that its components cannot be altered by simple distillation, This happens because when an azeotrope is barred, the vapour has the same proportions of constituents as the unboiled mixture.
Azeotropes are also called constant boiling mixture,
Rectified spirit is an azeotropic mixture of ethanol and water. 

d- tartaric acid and l - tartaric acid can be separated by:

methods of purification of organic compounds methods of purification - organic compounds organic chemistry - some basic principles and techniques organic chemistry : some basic principles and techniques chemistry biochemical techniques

  1. salt formation

  2. fractional distillation

  3. fractional crystallisation

  4. chromatography

Show answer
Correct Option: A
Explanation:

d- tartaric acid and l - tartaric acid can be
separated by Salt formation.
Two enantiomers of sodium ammonium salt of tartaric acid give rise to two distinctly different types of chiral crystals that can be easily separated.

The best solvent for the crystallization of organic solid is in which:

methods of purification of organic compounds methods of purification - organic compounds organic chemistry - some basic principles and techniques organic chemistry : some basic principles and techniques chemistry biochemical techniques

  1. organic compound is highly soluble

  2. compound is soluble on warming

  3. compound is soluble at $90^{0}$

  4. compound is insoluble

Show answer
Correct Option: B
Explanation:

Generally speaking you need to take polar solvents for polar compound and nonpolar solvents for nonpolar compounds. Many times a mixture of solvents works better. Once you have this basic idea, crystallization is a skill developed over a period of time by trial and error process. Even after long experience you may not hit the right solvent in the first try.

In fractional distillation of petroleum, the vapours with highest boiling point ____________.

methods of purification of organic compounds methods of purification - organic compounds organic chemistry - some basic principles and techniques organic chemistry : some basic principles and techniques chemistry biochemical techniques

  1. condense in upper most portion'

  2. condense in lower most portion

  3. condense in middle portion

  4. none of these

Show answer
Correct Option: B
Explanation:

The fractional column is hot at the bottom and cool at the top. Substances with high boiling points condense at the bottom and substances with lower boiling points condense on the way to the top.

Which of the following method is used for the purification of solids?

methods of purification of organic compounds methods of purification - organic compounds organic chemistry - some basic principles and techniques organic chemistry : some basic principles and techniques chemistry biochemical techniques

  1. Distillation under reduced pressure

  2. Distillation

  3. Steam distillation

  4. Sublimation

Show answer
Correct Option: D
Explanation:

Sublimation is the process in which solid gets converted into vapours directly without passing through the liquid state.

Which of following is incorrectly matched?

methods of purification of organic compounds methods of purification - organic compounds organic chemistry - some basic principles and techniques organic chemistry : some basic principles and techniques chemistry biochemical techniques

  1. Distillation - Liquids stable at their boiling point

  2. Distillation under reduced pressure - Liquids that decompose at their boiling point

  3. Steam distillation - Liquids that are immiscible with water

  4. All are true

Show answer
Correct Option: D

There is a mixture of three solid compounds A, B and C. Out of these compounds A and Care soluble in water and compound C is sublimable also. In what sequence the following techniques can be used for their effective separation? 
I. Filtration
II. Sublimation
IIl. Crystallisation from water extract
IV. Dissolution in water

methods of purification of organic compounds methods of purification - organic compounds organic chemistry - some basic principles and techniques organic chemistry : some basic principles and techniques chemistry biochemical techniques

  1. (II), (I), (IV), (III)

  2. (IV), (I), (II), (III)

  3. (I), (II), (III), (IV)

  4. (II), (IV), (I), (III)

Show answer
Correct Option: D
Explanation:

Sublimation will separate C from A and B. On adding water, A will dissolve but B will not. B can be separated by filtration. A will be present in the filtrate and can be obtained by crystallisation from water extract.

What cant be removed after distillation of water?

methods of purification of organic compounds methods of purification - organic compounds organic chemistry - some basic principles and techniques organic chemistry : some basic principles and techniques chemistry biochemical techniques

  1. Suspensions

  2. Precipitates

  3. Volatile liquids like alcohol

  4. Dissolved salts

Show answer
Correct Option: C
Explanation:

Distillation is the process of purifying water by removing contaminants.

A volatile liquid has a comparatively smaller boiling point than the water thus it becomes difficult to separate them. 

Silt in water remains suspended. It is removed by sedimentation and filtration. For increasing its sedimentation aluminium sulphates and calcium hydroxide (slaked lime) are added. As a result sticky aluminium hydroxide.

methods of purification of organic compounds methods of purification - organic compounds organic chemistry - some basic principles and techniques organic chemistry : some basic principles and techniques chemistry biochemical techniques

  1. Destroys slit particles

  2. Attracts the particles of slit

  3. Mixes with slit particles

  4. Makes slit particles increases in size and deposit at the bottom

Show answer
Correct Option: B
Explanation:

The silt in $H _2O$ remains suspended. To attract some more silt particles, $Al(OH) _3$ is used. It is used to absorb the silt particles and make the liquid more pure.

Which of the following is a physico-chemical method of separation and purification?

methods of purification of organic compounds methods of purification - organic compounds organic chemistry - some basic principles and techniques organic chemistry : some basic principles and techniques chemistry biochemical techniques

  1. Electrolysis

  2. Distillation in a flask or a big tower

  3. Filtration through a filtering medium

  4. Leaching

Show answer
Correct Option: A
Explanation:

Electrolysis is the only physico-chemical method. Rest all are physical processes.

Refining of petroleum does not involve.

methods of purification of organic compounds methods of purification - organic compounds organic chemistry - some basic principles and techniques organic chemistry : some basic principles and techniques chemistry biochemical techniques

  1. Simple distillation

  2. Steam distillation

  3. Fractional distillation

  4. Distillation under reduced pressure

Show answer
Correct Option: A,C,D
Explanation:

The steam distillation process works on the principle that when a mixture of two or more undissolved liquids are heated, while ensuring that the surfaces of both liquids are in contact with the atmosphere, the vapor pressure exerted by the system increases. This method is used for the refining of petroleum. 


So, simple distillation, fractional distillation, distillation under reduced pressure are not involved in the refining of petroleum.

Options A, C, and D are correct answers.

Select the correct code by matching list I and list II.


 List -I    List -II
A) Fractional Distillation a) A liquid having sufficiently different boiling points
 B) Fractional Crystallization b) Solids having different solubilities
 C) Vacuum Crystallization c) A liquid that decomposes at its boiling point
 D) Solvent extraction d) Liquids of almost same boiling points

methods of purification of organic compounds methods of purification - organic compounds organic chemistry - some basic principles and techniques organic chemistry : some basic principles and techniques chemistry biochemical techniques

  1. A - a, B - b, C - c, D - d

  2. A - a, B - c, C - b, D - d

  3. A - d, B - c, C - b, D - a

  4. A - b, B - d, C - c, D - a

Show answer
Correct Option: C
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