Q: A mixture of 2 mL ethyl acetate ($$\epsilon = 6.0) $$and 3 mL hexane ($$\epsilon = 1.99) is $$prepared. What is the dielectric constant of the mixture?

$$\epsilon_{mixture} = \frac{2 \times 6.0 + 3 \times 1.99}{5} = 3.6$$

Question 1

Which of the following best describes the principle behind column chromatography as used in the separation of plant pigments?

Accepted Answer

Components are separated based on their affinity to the stationary phase and their polarity.

Question 2

In the experiment, silica gel is used as the stationary phase. What property of silica gel makes it suitable for separating plant pigments?

Accepted Answer

Silica gel is highly polar, allowing polar compounds to interact more strongly and move slower.

Question 3

Given the dielectric constants in Table 1, which solvent would move the most polar pigment fastest through the column?

Accepted Answer

Dichloromethane ($$\epsilon = 8.93)$$

Question 4

A mixture of 2 mL ethyl acetate ($$\epsilon = 6.0) $$and 3 mL hexane ($$\epsilon = 1.99) is $$prepared. What is the dielectric constant of the mixture?

Accepted Answer

$$\epsilon_{mixture} = \frac{2 	imes 6.0 + 3 	imes 1.99}{5} = 3.6$$

Question 5

During the experiment, why is it important to tap the column lightly after adding the silica gel and solvent?

Accepted Answer

To ensure the silica gel is evenly distributed and to remove air bubbles that could disrupt the flow.

Question 6

If a pigment elutes first using hexane/dichloromethane (1:1), what can you infer about its polarity compared to other pigments in the mixture?

Accepted Answer

It is less polar than the other pigments.

Question 7

Which of the following is the correct order of elution for pigments in column chromatography using increasing polarity of eluting agents?

Accepted Answer

Nonpolar pigments elute first, followed by polar pigments as the polarity of the eluent increases.

Question 8

What is the role of anhydrous sodium sulfate in the extraction of plant pigments?

Accepted Answer

It acts as a drying agent to remove water from the organic layer.

Question 9

Why is it necessary to discard the silica gel and any remaining eluting agents into the waste disposal bin after the experiment?

Accepted Answer

Silica gel and solvents may contain hazardous residues and must be disposed of properly.

Question 10

A student observes that the colored bands in the column are not separating well. Which of the following is the most likely cause?

Accepted Answer

The eluting agent is too polar, causing all pigments to elute together.

Question 11

Which pigment is most likely to be found in the green band when separating unripe red pepper pigments?

Accepted Answer

Chlorophyll

Question 12

In the context of column chromatography, what is the mobile phase?

Accepted Answer

The solvent or mixture of solvents that moves through the column.

Question 13

Which of the following statements about the separation of capsaicin and capsorubin in red pepper is correct?

Accepted Answer

Capsaicin and capsorubin are separated based on their different polarities using column chromatography.

Question 14

A student prepares a column but notices that the solvent level is below the top of the silica gel before loading the sample. What is the most likely consequence?

Accepted Answer

The separation will be poor because the silica gel is not fully wetted.

Question 15

If the eluting agent is changed from hexane/dichloromethane (1:1) to dichloromethane/methanol (1:1), what effect does this have on the separation?

Accepted Answer

It increases the polarity of the mobile phase, allowing more polar pigments to elute.

Question 16

Which of the following is a correct safety precaution when handling dichloromethane (DCM) in the experiment?

Accepted Answer

Work in a well-ventilated area or fume hood to avoid inhalation of vapors.

Question 17

Why is it important to add the pigment extract dropwise onto the column rather than all at once?

Accepted Answer

To prevent overloading the column and ensure better separation of pigments.

Question 18

Which of the following best explains why more polar solvents elute polar compounds faster in column chromatography?

Accepted Answer

Polar solvents compete with polar compounds for adsorption sites on the stationary phase, reducing retention.

Question 19

A student uses toluene ($$\epsilon = 2.38) as $$the eluting agent. What is the expected effect on the separation of highly polar pigments?

Accepted Answer

Highly polar pigments will be strongly retained and elute slowly.

Column Chromatography of Plant Pigments: Principles, Procedures, and Analysis

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