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Experiemnt CSeparating a Mixture by Thin Layer Chromatography

Lab Report

Name: Chui Wai

Student ID: 2012600412

Group Member:

Date of Experiment: 20/03/2014 Demonstrator: Samantha Chan

Data Sheet

Sketch of Chromatograms

A B C D E

Ethyl acetate hexane methanol dichloromethane toluene

Optimal solvent system: E: toluene

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Reference Materials Analysis

Biphenyl 4-Phenylphenol Benzophenone

(M) (N) (O)

Distance traveled by sample (mm) 38 8 25.5

Distance traveled by solvent from (mm) 46.5 46.5 46.5

Rf value 0.817 0.172 0.548

Unknown Sample Analysis

Component 1

(if any)

Component 2

(if any)

Component 3

(if any)

Distance traveled by sample (mm) 7 38.5 7.5 25.5 26.5 37

Distance traveled by solvent from (mm) 47 47 47 47 47 47

Rf value 0.149 0.819 0.160 0.543 0.564 0.787

Identity N M N O O M

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Results & Discussion

1 a) Rank the polarity of reference M – O in ascending order.

b) According to the Rf values obtained, explain how the compound structures affect their Rf in the chosen solvent.

a) M < O < N

b) The more polar the organic compound is, the smaller the Rf value of the organic compound.

The silica gel is a polar compound and due to the theory of “like dissolve like”, polar compounds tend to interact with polar compounds. As the chosen solvent is non-polar, therefore the solvent will not have interaction with silica gel.

M is a symmetrical compound which is non-polar, it is washed up by the solvent without any attraction from silica gel, and thus it moved up faster, having a large Rf.

However, N and O are polar compounds. The -OH bond in the compound give N a high polarity. O is a symmetrical compound but it has pairs of free electron from oxygen atom which makes O being polarized.N is a linear structure and O is much bulky than N.

As a result, N has a greater polarity than O. As the solvent moving up, N experience more attraction from the silica gel than O does and hence move slower than N and therefore has a smaller Rf.

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2 For the two visualization methods mentioned in this experiment, state the limitation (if any) for each of them. Also suggest any precautions in carrying out these methods.

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1) UV fluorescence.

Not all chemical components are sensitive to the UV light and only the sensitive one can be visualized. On the other hand, some chemicals are very sensitive to the UV light and will immediately decomposed when high energy UV light shined on it. UV light is harmful to the human body which will cause skin cancer or skin burning.

Therefore, we better wear sun glass or goggles to protect our eyes and wear gloves to protect out hands which will exposed under the UV light. Switch off the device once you finished the experiment.

2) Iodine staining

Some chemical components does not react with Iodine and hence no result will be observed. And iodine vaporized quickly. If the reaction time between the chemical and iodine is slower than the vaporization speed of the iodine, the result shown will not be accurate.

Iodine is toxic and cause harmful effect to the human body. So goggle is needed to protect the eyes and gloves should be wore to avoid direct contact between the hand skin and iodine. Also such process should undergo inside a fume cupboard to prevent inhale the iodine vapour.

3 Predict and explain the effect of increasing the polarity of solvent on the mobility of organic compounds on silica gel.

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Increase in the polarity of the solvent will increase the mobility of organic compound on silica gel. Increasing the polarity of the solvent will reduce the interaction between the silica gel and the organic compounds thus increasing the mobility.

When a higher polarity solvent is used, the interaction between the silica gel and the polar organic compounds is significantly reduced or can be said that is replaced by. Thus higher polarity of solvent will increased the mobility of organic compounds. For non-polar compounds, it will just wash up by the solvent without any interaction with the silica gel.

4 Explain what a mixed solvent system is and state its possible advantages over single solvent system.

A mixed solvent system is the solvent system with more than one solvent mixed together with a fixed ratio.

Some compounds has similar solubility in the same solvent but different solubility in another solvent. By using a mixed solvent system, a better separation can be obtained. Thus, a better recognition of components can be done. Also, using a mixed solvent system, the polarity of solvent can be find tuned to an appropriate polarity you want.

End

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