Methods of Purification of Organic Reaction Mechanism Question And Answers – NEET General Organic Chemistry

Methods Of Purification Of Organic Reaction Mechanism

Question 1. The function of boiling the sodium extract with conc. HNO3 before testing for the presence of halogen is

1. To make the solution acidic
2. To make the solution clear
3. To convert Fe²⁺ to Fe⁽³⁺⁾
4. To destroy CN^– and S^2- ions

Answer: 4. To destroy CN^– and S^2- ions

Solution: Sodium extract is boiled with dilute HNO₃ before testing for halogens to decompose NaCN or Na₂S present in the Lassaigen’s extract otherwise these will produce a white ppt. with AgNO₃ and interfere with the test of halogens.

Read And Learn More: NEET General Organic Chemistry Notes, Question And Answers

Question 2. A mixture of camphor and benzoic acid can be separated by

1. Sublimation
2. Extraction with a solvent
3. Chemical method
4. Fractional crystallization

Answer: 3. Chemical method

Solution: Aqueous solution of NaHCO₃ can be used to separate benzoic acid from its mixture with camphor. Benzoic acid form water-soluble sodium benzoate with NaHCO₃.

Question 3. Which method is used to separate the sugars?

1. Fractional crystallization
2. Sublimation
3. Chromatography
4. Benedict’s reagent

Answer: 3. Chromatography

Solution: Chromatographic methods are used to separate the sugars.

Question 4. Chromatography was discovered by

1. Kekule
2. Pauling
3. Rutherford
4. Tswett

Answer: 4. Tswett

Solution: It’s a fact

Question 5. The relative adsorption of each component in the mixture is expressed in terms of

1. Adsorption Factor
2. Retention Factor
3. Co-Factor
4. Sorption Factor

Answer: 2. Retention Factor

Solution: In thin-layer chromatography, the relative adsorption of each component of the mixture is expressed in terms of retention factor (Rf)

Question 6. A mixture of oil and water is separated by

1. Filtration
2. Fractional distillation
3. Sublimation
4. Using separating funnel

Answer: 4. Using a separating funnel

Solution: Oil and water are immiscible liquids, thus are separated using a separating funnel

Question 7. Sublimation is a process in which a solid

1. Changes into vapor form
2. Changes into another allotropic form
3. Changes into liquid form
4. None of the above

Answer: 1. Changes into vapor form

Solution: It’s a fact

Question 8. Anthracene is purified by

1. Filtration
2. Distillation
3. Crystallization
4. Sublimation

Answer: 4. Sublimation

Solution: The compound that sublimes on heating can be purified by sublimation method. Benzoic acid, camphor and naphthalene sublime on heating hence, they are purified by the sublimation method.

Question 9. Steam distillation is based on the fact that the vaporization of organic liquid takes place at

1. Lower temperature than its boiling point
2. A higher temperature than its boiling point
3. Its boiling point
4. Water and organic liquid both undergo distillation

Answer: 1. Lower temperature than its boiling point

Solution: Organic compounds which are volatile in steam can be purified by steam distillation. It is based on the fact that the vaporization of organic liquid takes place at a lower temperature than its boiling point

Question 10. A mixture of iron fillings and sulfur cannot be separated by

1. Heating
2. Magnet
3. Shaking with CS₂
4. Washing in a current of water

Answer: 1. Heating

Solution: The properties of iron and sulphur do not change when they are separated. There is no formation of a new product in this change. There is no change in the heat energy level of the mixture. The change is temporary and reversible as iron and sulphur can be mixed again.

Question 11. Essential oils can be isolated by

1. Crystallization
2. Steam distillation
3. Sublimation
4. Distillation

Answer: 2. Steam distillation

Solution: The extraction of essential oils is generally carried out by two main techniques: azeotropic distillation (hydro distillation, hydro diffusion, and steam distillation) and extraction with solvents. These traditional methods are a bit expensive, especially since they are extremely energy and solvent-consuming.

Question 12. Protein solvent is

1. Diethyl ether
2. n-hexane
3. Acetone
4. Ethanol

Answer: 4. Ethanol

Solution: H₂O, ROH, R-COOH etc. are protic solvents because they are polar in nature and contain hydrogen directly bonded to oxygen while others are aprotic solvents as they do not have hydrogen bonded directly to oxygen. They are especially favorable for S_N1 reactions. While aprotic solvents cannot have hydrogen bond to the nucleophile because they do not have hydrogen bonded to nitrogen or oxygen. They are favorable for S_N2 reactions.

Question 13. Many organic compounds are prepared by using PCl₅ because:

1. “OH” group of alcohol is easily replaced by the chlorine atom
2. Chlorines are added to the unsaturated compounds
3. It removes water from the organic compounds
4. Phosphorus atoms are entered in the alcohol

Answer: 1. “OH” group of alcohol is easily replaced by the chlorine atom

Solution: Substitution of –OH group from a substrate can be easily made by PCl₅.

Question 14. Which of the following are most commonly used to dry organic liquids?

1. Lithium
2. Sodium
3. Potassium
4. Rubidium

Answer: 2. Sodium

Solution: Na reacts with water less violently than K and Rb.

Question 15. Naphthalene can be easily purified by

1. Sublimation
2. Crystallization
3. Distillation
4. Vaporization

Answer: 1. Sublimation

Solution: Substances that sublime on heating are usually purified by sublimation. Hence, naphthalene is purified by sublimation.

Question 16. The chromatography technique is used for the separation of

1. Small Sample of mixture
2. Plant pigments
3. Dyestuff
4. All of the above

Answer: 4. All of the above

Solution: It is capable of separating all the components of a multicomponent chemical mixture without requiring extensive foreknowledge of the identity, number, or relative amounts of the substances present.

Question 17. An organic compound on heating with CuO produces CO₂ but no water. The organic compound may be

1. Carbon tetrachloride
2. Chloroform
3. Methane
4. Ethyl iodide

Answer: 1. Carbon tetrachloride

Solution: Since, the compound on heating with CuO produces CO₂, it contains carbon. Again, it does not produce water, hence it does not contain hydrogen. So, the organic compound is carbon tetrachloride (CCl₄).

Question 18. Vacuum distillation is used to purify liquids which

1. Are highly volatile
2. Are explosive in nature
3. Decompose below their boiling points
4. Have a high boiling point

Answer: 3. Decompose below their boiling points

Solution: If a liquid decomposes at or below its boiling point, it is purified by vacuum distillation

Question 19. Which among the following substances are purified by sublimation?

1. Benzoic acid
2. Camphor
3. Naphthalene
4. All of these

Answer: 4. All of these

Solution: Compounds that sublime on heating can be purified by the sublimation method. Benzoic acid, camphor, and naphthalene sublime on heating hence, they are purified by the sublimation method.

Question 20. In a solution, solvent can be separated from solute by which of the following processes?

1. Decantation
2. Filtration
3. Distillation
4. Sedimentation

Answer: 3. Distillation

Solution: Distillation is applied if the organic liquid is stable at its boiling point and contains a nonvolatile impurity

Question 21. Adsorbent is made of … in TLC

1. Silica gel
2. Alumina
3. Both (1) and (2)
4. None of these

Answer: 3. Both (1) and (2)

Solution: In TLC, the adsorbent is made of silica gel or alumina gel

Question 22. Absolute alcohol cannot be obtained by simple fractional distillation because

1. Pure C₂ H₅OH is unstable
2. C₂H₅OH forms hydrogen bonds with water
3. The boiling point of C₂ H₂OH is very close to that of water
4. The constant boiling azeotropic mixture is formed with water

Answer: 4. Constant boiling azeotropic mixture is formed with water

Solution: The components of an azeotropic mixture are separated by a special method, i.e., fractional distillation. The simple fraction which distills at 337.8 K is a ternary azeotrope consisting of all water. Some alcohol and benzene.

Question 23. A mixture of iodine and sodium chloride can be easily separated by

1. Fractional distillation
2. Steam distillation
3. Chromatography
4. Sublimation

Answer: 4. Sublimation

Solution: Sublimation is the process employed for those solids that convert directly into vapors on heating without converting into the liquid phase.

Question 24. Which of the following processes is suitable for the purification of aniline?

1. Simple distillation
2. Fractional distillation
3. Fractional crystallization
4. Steam distillation

Answer: 4. Steam distillation

Solution: Those organic compounds, which are volatile in steam are purified by steam distillation. Since aniline is a steam-volatile compound, it is purified by steam distillation.

Question 25. Amongst the following compounds, which can be easily sulphonated?

1. Benzene
2. Toluene
3. Nitrobenzene
4. Chlorobenzene

Answer: 2. Toluene

Solution: In toluene (-CH₃) group is present which has a +I effect and increases electron density on ortho and para position. While in sulphonation – SO₃ acts as an electrophile, it (-SO₃H) attacks on ortho and para position readily.

Question 26. The best method to separate the mixture of ortho-and-para nitrophenol (1:1) is

1. Vaporization
2. Color spectrum
3. Distillation
4. Crystallization

Answer: 3. Distillation

Solution: Ortho and para-nitrophenol are separated by distillation because p-nitrophenol has a higher boiling point than o-nitrophenol due to the H-bonding.

Question 27. Which of the following reagents will be fruitful for separating a mixture of nitrobenzene and aniline?

1. Aq. NaHCO₃
2. H₂O
3. Aq. HCl
4. Aq. NaOH

Answer: 3. Aq. HCl

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

Aniline + aq. HCl→ salt, which is water soluble

Nitrobenzene +aq. HCl→ no reaction

∴ aq. HCl is used to separate aniline and nitrobenzene.

Question 28. Fractional distillation is a process by which the separation of different fractions from mixtures of solutions is carried out by making use of one of the properties.

1. Freezing point
2. Boiling point
3. Melting point
4. Solubility

Answer: 2. Boiling point

Solution: Distillation is used to purify liquids based on differences in their boiling points. When the boiling points of liquids are very close to each other, then fractional distillation is used.

Question 29. Sublimation can’t be used for the purification of

1. Benzoic acid
2. Camphor
3. Urea
4. Naphthalene

Answer: 3. Urea

Solution: Only urea does not sublime while naphthalene, camphor and benzoic acid do

Question 30. Fractional crystallization are carried out to separate a mixture of

1. Organic solids mixed with inorganic solids
2. Organic solids slightly soluble in water
3. Organic solids have a small differences in their solubilities in a suitable solvent
4. Organic solids have great differences in their solubilities in a suitable solvent

Answer: 3. Organic solids have small difference in their solubilities in a suitable solvent

Solution: Fractional crystallization is used to purify organic solids which dissolve in a particular solvent. But their rate of solubility is different

Question 31. Glycerol can be separated from spent lye in soap industry by

1. Steam distillation
2. Fractional distillation
3. Distillation under reduced pressure
4. Ordinary distillation

Answer: 3. Distillation under reduced pressure

Solution: Glycerol can be separated from spent lye in the soap industry by distillation under reduced pressure because it decomposes near its boiling point.

Question 32. Fractional distillation is useful in the distillation of

1. Petroleum
2. Coal-tar
3. Crude alcohol
4. All of these

Answer: 4. All of these

Solution: Fractional distillation is used for the separation of crude petroleum into various fractions like coal-tar, crude alcohol and petroleum

Question 33. Which of the following solvents are aprotic?

1. NH₃

2. SO₂

3. CH₃CN

4. CH₃CO₂H

1. 1, 2, 3
2. 1, 3, 4
3. 2, 3
4. 1, 3

Answer: 1. 1, 2, 3

Solution: A solvent molecule lacking a polar X-H bond is called aprotic solvent. NH₃, SO,₂ and CH₃CN are aprotic solvent while CH₃COOH is a protic solvent.

Question 34. An unknown compound A has a molecular formula C₄ H₆. When A is treated with excess of Br₂ a new substance B with formula C₄ H₆ Br₄ is formed. A forms a white ppt. with ammoniacal silver nitrate solution. A may be:

1. But-1-yne
2. But-2-yne
3. But-1-ene
4. But-2-ene

Answer: 1. But-1-yne

Solution: A white precipitate with AgNO3 confirms the presence of terminal alkyne.

An unknown compound A has a molecular formula C₄ H₆. When A is treated with excess of Br₂ a new substance B with formula C₄ H₆ Br₄ is formed. A forms a white ppt. with ammoniacal silver nitrate solution. A may be But-1-yne

Question 35. The sodium extract of an organic compound on treatment with FeSO₄ solution, FeCl_3, and HCl gives a red solution. The organic compound contains

1. Both nitrogen and sulphur
2. Nitrogen only
3. Sulphur only
4. Halogen

Answer: 1. Both nitrogen and sulphur

Solution: Ferric chloride reacts with sodium thiocyanate to form ferric thiocyanate which is blood red in color. This test can be used as a confirmatory test for organic compounds containing both nitrogen and sulfur.

NaCN+S_(g)(Δ) → NaSCN_{(Sodium thiocyanate)}
Fe⁺³ +3NaSCN → Fe(SCN)_{3(ferric thiocyante)(red colour)}

Question 36. A mixture of acetone and methanol can be separated by

1. Steam distillation
2. Vacuum distillation
3. Fractional distillation
4. None of these

Answer: 3. Fractional distillation

Solution: Acetone and methanol have nearly equal boiling points thus, they are separated by fractional distillation

Question 37. In paper chromatography

1. The mobile phase is liquid and the stability phase is solid
2. The mobile phase is solid and the stationary phase is liquid
3. Both phases are liquids
4. Both phases are solids

Answer: 3. Both phases are liquids

Solution: Paper chromatography is a special case of partition chromatography where the special quality paper containing water trapped in it acts as a stationary phase and solvent as a mobile phase. Thus, both phases are liquids.

Question 38. Which of the following processes is not used for the purification of solid impurities?

1. Distillation
2. Sublimation
3. Crystallization
4. Vaporization

Answer: 1. Distillation

Solution: The distillation process is not used for the purification of solid impurities. It is used for the purification of liquids that boils without decomposition and contain non-volatile impurities.

Question 39. A liquid decomposes at its normal boiling point. It can be purified by

1. Sublimation
2. Steam distillation
3. Vacuum distillation
4. Fractional distillation

Answer: 3. Vacuum distillation

Solution: A liquid, which decomposes at its normal boiling point can be purified by vacuum distillation.

Question 40. A mixture of o-nitrophenol and p-nitrophenol can be separated by

1. Fractional crystallization
2. Sublimation
3. Chemical separation
4. Steam distillation

Answer: 4. Steam distillation

Solution: In a mixture of o-nitrophenol, and p-nitrophenol, o-nitrophenol is steam volatile due to intra-molecular hydrogen bonding whereas p-nitrophenol is less volatile due to intermolecular hydrogen bonding.

Question 41. Which of the following is useful for making pure water from a solution of salt in water?

1. Filtration
2. Distillation
3. Chromatography
4. Steam distillation

Answer: 2. Distillation

Solution: Distillation can be used to obtain pure water from a solution of salt in water. During distillation, water is evaporated by heating. The evaporated water vapors are condensed and collected in the receiving flask. Salt remains in the distillation flask.

Question 42. A mixture of sugar and common salt is separated by
crystallization by dissolving in

1. H₂O
2. C₂H₅OH
3. C₅O₆
4. None of these

Answer: 2. ₂H₅OH

Solution: When a mixture of sugar and common salt has to be separated using simple crystallization, we use ethanol as a suitable solvent; at 75°C sugar is soluble in ethanol and NaCl is not, so it’s sugar that crystallizes out.

Question 43. For the purification, isolation, and separation of organic compounds, the latest technique is

1. Chromatography
2. Steam distillation
3. Fractional crystallization
4. Sublimation

Answer: 1. Chromatography

Solution: Chromatography is a modern technique used for the separation of mixtures into its components, purification of compounds and also to test the purity of compounds.

Question 44. The best method for the separation of naphthalene and benzoic acid from their mixture is

1. Chromatography
2. Crystallization
3. Distillation
4. Sublimation

Answer: 2. Crystallization

Solution: Naphthalene and benzoic acid cannot be separated by the sublimation method because the naphthalene and benzoic acid both are sublimes on heating. They are separated by hot water in which benzoic acid dissolves but naphthalene does not.

Question 45. Impure glycerine can be purified by

1. Steam distillation
2. Simple distillation
3. Vacuum distillation
4. Extraction with a solvent

Answer: 3. Vacuum distillation

Solution: If a liquid decomposes at or below its boiling point, it is purified by vacuum distillation, impure glycerine is purified by this method

Assertion – Reasoning Type:

Each Question contains statement 1(Assertion) And Statement 2(Reason). Each Question has 4 choices 1. , 2. , 3., and 4. out of which ONLY ONE is correct.

1. Statement 1 is True; Statement 2 is True; Statement 2 is correct
   Explanation for Statement 1
2. Statement 1 is True; Statement 2 is True; Statement 2 is not the correct explanation for Statement 1
3. Statement 1 is True, Statement 2 is False
4. Statement 1 is False, Statement 2 is True

Question 46

• Statement 1: Benzoic acid is purified by the sublimation process
• Statement 2: The sublimation process is very useful in separating a volatile solid from a non-volatile solid

Answer: 1. Statement 1 is True; Statement 2 is True; Statement 2 is the correct explanation for Statement 1

Solution: In sublimation, certain substances when heated, first directly convert from the solid to the vapor state without melting. The vapor when cooled, gives back the solid substance

Matrix-Match Type:

Question 47. Compare List 1 and List 2 and choose the correct matching codes from the choices given

Codes:

1. 5, 4, 1, 2, 3
2. 4, 5, 1, 6, 3
3. 6, 4, 1, 3, 3
4. 5, 4, 6, 2, 3
5. 4, 6, 2, 3, 3

Answer: 1. 5,4,1,2,3

Solution: Sublimation is the conversion of solid directly into the gaseous phase. The liquid state does not exist.

Examples: naphthalene, and anthracene.

The Bilstein test is a simple chemical test for halogens.

Victor-Meyer’s method, Standard laboratory methods are for determining the molecular weight of a volatile liquid.

Steam distillation is for the volatile constituents of a liquid.

It is a special type of distillation for temperature-sensitive materials like aromatic natural compounds. e.g., ortho nitrophenol, cinnamaldehyde.

Vacuum distillation at reduced pressure is generally used in the case of high boiling liquids that decompose below their normal boiling points and cannot be purified by distillation at atmospheric pressure e.g., glycerol.

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 the amount of O₂ in it