Class 11 Chemistry MCQ – Methods of Purification of Organic Compounds

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This set of Class 11 Chemistry Chapter 12 Multiple Choice Questions & Answers (MCQs) focuses on “Methods of Purification of Organic Compounds”.

1. The purification method where solid substances change from solid to vapor state without passing through the liquid state is called as which of the following?
a) Sublimation
b) Crystallization
c) Distillation
d) Differential extraction
View Answer

Answer: a
Explanation: In sublimation, the solid substance transforms directly to the vapor state without entering into the liquid state. This helps in separating sublimable compounds from non-sublimable ones. Whereas the other three, i.e. crystallization, distillation and differential extraction are used when a suitable solvent is involved. In other words, they deal with mainly liquids and not solids alone.

2. In crystallization, the compound dissolved in a solvent is more soluble in what temperature?
a) Room temperature
b) Lower temperature
c) Higher temperature
d) Very low temperature
View Answer

Answer: c
Explanation: When a compound is dissolved in water, solubility increases with increase in temperature. This is because, when the temperature increases, the kinetic energy also increases which in turn helps the solvent molecules to break apart the solute molecules more efficiently than in other cases. These solute molecules are held together by intermolecular interactions which requires greater energy to be broken off and hence, higher temperature.

3. What is the basis for the process of distillation?
a) Difference in melting point
b) Difference in temperature
c) Difference in pressure
d) Difference in boiling point
View Answer

Answer: d
Explanation: The process of distillation is based on the difference in the boiling points of the liquids. This is because, liquids having different boiling points vaporize at different temperatures. In this way, the vapors cooled can be collected separately from the liquid formed. Crystallization is used to separate volatile liquids from non-volatile liquids as well.
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4. In fractional distillation, vapors of low boiling point component ascend to the top of the column.
a) True
b) False
View Answer

Answer: a
Explanation: Fractional distillation, like normal distillation is also based on the difference in boiling point of the liquids. The only difference in fractional distillation is that, the liquids associated with this method have lesser difference in boiling point than the liquids involved in normal distillation. So, the high boiling point liquids condense at the bottom while the low boiling point liquid condense all the way to the top of the distillation column.

5. Identify the example of compounds separated by steam distillation method.
a) Glycerol-spent lye mixture in soap industry
b) Aniline-water mixture
c) Chloroform and aniline mixture
d) Different fractions of crude oil in petroleum industry
View Answer

Answer: b
Explanation: Aniline and water mixture is separated by employing the process of steam distillation. Steam distillation method is used when the substances involved are steam volatile and immiscible in water. Aniline satisfies both these conditions and, hence, this method is used to separate aniline from aniline-water mixture. Glycerol-spent lye mixture is an example of distillation under reduced pressure, chloroform and aniline mixture employs simple distillation, and crude oil separation involves fractional distillation method.
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6. Which of the following is the apparatus for differential extraction?
a) Separatory funnel
b) Porous sheet
c) Packed column
d) Electric motor
View Answer

Answer: a
Explanation: A seperatory funnel is used in differential extraction. Differential extraction involves separating the immiscible organic compound from the aqueous solvent. The separating funnel aids in this process of separating immiscible liquids. It also helps in layer formation, with the denser solvent at the bottom and the other on top. This layer formation is important for the process, and thus, separatory funnel is chosen as the apparatus for differential extraction.

7. Which is not used as an absorbent in adsorption chromatography?
a) Silica gel
b) Alumina
c) Potassium permanganate
d) Starch
View Answer

Answer: c
Explanation: A good adsorbent requires large surface area, should be easily available, less expensive. They should also be thermally stable, and have high abrasion resistance. Silica, alumina, and starch possesses these characteristics while potassium permanganate does not, so it cannot be an adsorbent.
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8. In column chromatography, identify the mobile and stationary phase from the following.
a) Solid, Liquid
b) Liquid, Solid
c) Gas, Liquid
d) Solid, Solid
View Answer

Answer: b
Explanation: In column chromatography, the mobile phase is made out of liquid or a mixture of liquids which is allowed to flow down the column, and the stationary phase consists of solid, that is the adsorbent(alumina or silica gel) over which the liquid(mobile phase) flows.

9. Thin layer chromatography is used to estimate drugs in formulation.
a) True
b) False
View Answer

Answer: b
Explanation: Estimation of drugs in formulation is done by column chromatography. Thin layer chromatography is used to detect amino acids by spraying the glass plate with ninhydrin solution. Thin layer chromatography involves the use of a glass plate, called as chromaplate.
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10. Paper chromatography is a type of which chromatography?
a) Column chromatography
b) Thin layer chromatography
c) Adsorption chromatography
d) Partition chromatography
View Answer

Answer: d
Explanation: Paper chromatography is a type of partition chromatography. This is because, they spend more time in the stationary phase than the mobile phase. Also, they won’t travel very fast up the paper. Partition chromatography employs the method of separation by making use of the partition of the solutes between the two liquid phases.

11. The mobile phase in chromatography can comprise of which of the following?
a) Gas or liquid
b) Liquid or solid
c) Solid or gas
d) Liquid only
View Answer

Answer: a
Explanation: The function of the mobile phase in chromatography is to flow over the stationary phase through the packed bed or column. So, only fluids (liquid or gas) can be employed as mobile phase whereas solids cannot be mobile phase, simply due to its inability to flow like fluids and also the interaction with the stationary phase (solid or liquid) will be affected and hence, solids cannot be used as mobile phase.

12. Which type of chromatography involves the separation of a mixture over a column of adsorbent packed in a glass tube?
a) Thin layer chromatography
b) Partition chromatography
c) Column chromatography
d) Gas liquid chromatography
View Answer

Answer: c
Explanation: Column chromatography involves the separation of a mixture over a column of adsorbent packed in a glass tube. The mixture adsorbed on the adsorbent is placed at the top of the column and the mobile phase is allowed to flow through the column slowly.

13. Gas chromatography can be performed in X, whereas liquid chromatography can be performed in Y. Identify X and Y.
a) X = only plane surfaces, Y = only columns
b) X = only columns, Y = only plane surfaces
c) X = only columns, Y = columns or plane surfaces
d) X = columns or plane surfaces, Y = only plane surfaces
View Answer

Answer: c
Explanation: Gas chromatography can be done only in columns because in this method, the sample is vaporized and injected onto the top of the chromatographic column. It could be gas-liquid or gas-solid chromatography. Liquid chromatography has liquid as the mobile phase where sample ions or molecules are dissolved. So, it can be carried out either in a column or a plane.

14. What is the paper strip developed in partition chromatography called?
a) Chromatograph
b) Chroma
c) Chromatographing strip
d) Chromatogram
View Answer

Answer: d
Explanation: The paper strip so developed by retaining different components according to their different partitions in the two phases is called a chromatogram. The spots of the separated colored components are visible at different lengths from the location of the initial point on the chromatogram.

15. Which is the most suitable carrier gas in gas chromatography?
a) Helium
b) Nitrogen
c) Oxygen
d) Carbon dioxide
View Answer

Answer: a
Explanation: In gas chromatography, the carrier gas should be an inert gas which does not react with the sample. Even though nitrogen and some other gases are also used, 90% of the instruments use helium as the carrier gas. Hydrogen is preferred for improved separations.

Sanfoundry Global Education & Learning Series – Chemistry – Class 11.

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