4A If your solution does not crystalize, write two steps to take that would ensu

Question

4A If your solution does not crystalize, write two steps to take that would ensure orytallantion SA Explain briefty the principle of counter ow in the condenser 6A. Why is phosphoric acid preferably used over suilfturic acid for the dehydration of cyclohexanol to In order compound using TLC.a sample of the pure compound must be spoted on the same plate as the unknown. Why is this necessary? 7A. to identify a 8A Why must the TLC chamber be covered? 9A. When using a separatory funnel with methylene chloride it is necessary to vent often. Why? 10A When using a Buchner funnel air is allowed to fow through the collected product for about ten to is minutes. Explain.

Explanation / Answer

4A. To initiate crystallization, we can (a) concentrate the solution further (b) add few crystals of pure compound for nucleation.

5A. When water flows backwards from outlet to inlet due to back pressure it is counter flow.

6A. Phosphoric acid is a weaker acid than sulfurric acid. Sulfuric acid is an oxidant and it also oxidizes the alcohol to produce side products.

7A. For comparison purpose pure compound must also be spotted on the tlc plate for identification of the unknown compound.

8A. TLC chamber is saturated with the mobile phase by coverying the chamber and to avoid solvent evaporation while the tlc is running.

9A. Methylene chloride has very low boiling point and it forms vapors/traps air in the separatory funnel, therefore, to equalize the pressure and to release the air the funnel is openned.

10A. Air is allowed to flow to dry the compound thoroughly and to remove any excess solvent in the compound.

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