Question

Describe why silica gel chromatography is Chem 08LA Lab Manual Winter 2020 Page | 21 a good method of separating methyl orange from biphenyl. Based on the structure of Biphenyl and Methyl Orange, predict which compound will have a higher Rf value on TLC and explain your choice.

Answer 1

Answer:

Silica gel chromatography is a s good method for separating these methyl orange and biphenyl because of the wide difference in their polarity. Biphenyl will give a higher Rf value because it is a non-polar and moves faster on silica gel.

Explanation:

Silica gel is very polar, so polar components (like methyl orange) interact with and move slowly it but non polar components (like biphenyl) move faster on silica gel. Looking at their chemical structures, methyl orange has a polar end while biphenyl is a non-polar hydrocarbon. During silica gel chromatography, the methyl orange will interact with silica gel and  move slowly but the biphenyl will move fast on the gel because it does not interact with silica gel. This will result to a very distinct separation of the components.

The biphenyl will therefore have a higher Rf value on TLC because it will move faster and longer on the TLC plate.

Answer 2

Complete Question

The complete question is shown on the first uploaded image

Answer:

The structure of Biphenyl and Methyl Orange is shown on the second uploaded image

Looking at the structures of both compound we can see that methyl orange is a polar compound due to the presence of  -SO₃Na functional group. This  -SO₃Na group is ionic in nature and imparts polarity to the methyl orange , while for biphenyl is a non-polar compound due to the absence of the polar functional groups in its structure

The technique silica gel chromatography is an excellent tool for the separation of molecules based on polarity differences.Silica gel(stationary state)is polar in nature.This means that non polar compounds tend to filter before more polar ones.looking at the case at hand biphenyl will filter first due to its non-polar nature and therefore would have high $R_{f}$  value on TCL(Thin-layer chromatography) plate

NOTE : $R_{f}$   means (The distance traveled by sample )/(The distance traveled by solvent(in its mobile phase)).

Explanation:

In order to get a better understanding let explain how TCL(Thin-layer chromatography) works

The TCL plate (stationary phase)  is made of  glass or plastic that is been coated by adsorbent material in this case of this experiment  a silica gel

Step one of the procedure is to apply the non- volatile mixture on the TCL plate then by capillary action the solvent(mobile phase which is mostly heptane a non-polar compound) is drawn up from the bottom of the plate to the top, because different molecules ascend the plate at different rates ,separation is achieved.