Question 1

What is the main principle of chromatography?

Accepted Answer

Chromatography separates compounds according to their different interactions with a stationary phase and a mobile phase. Because the components are adsorbed or absorbed to different extents, they travel at different rates and can be separated as bands or spots.

Question 2

How is Rf calculated in thin layer chromatography?

Accepted Answer

Measure the distance travelled by the centre of the spot from the baseline and divide it by the distance travelled by the solvent front from the same baseline. Rf has no unit and should be compared only for the same stationary phase, mobile phase and development conditions.

Question 3

Why must the TLC spotting line remain above the solvent level?

Accepted Answer

If the sample line touches the solvent reservoir, the sample can dissolve directly into the bulk mobile phase instead of being separated on the plate. The baseline must remain above the solvent so the mobile phase can rise by capillary action through the sample spots.

Question 4

What is the role of a separatory funnel in differential extraction?

Accepted Answer

A separatory funnel separates two immiscible liquid phases after extraction. The mixture is shaken, vented, and allowed to settle completely; then the layer containing the desired compound is collected separately, while the unwanted layer may be drained to a waste or temporary receiver.

Question 5

Why does the position of the organic layer change with ether or dichloromethane?

Accepted Answer

The denser liquid forms the lower layer and the less dense liquid forms the upper layer. Dichloromethane-rich liquid is denser than water, so it lies below the aqueous layer, whereas ether-rich liquid is less dense and lies above it.

Chromatography & Differential Extraction — Follow the Bands, Then Split the Layers

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