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Identification of an organic unknown

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Introduction

Identification of an organic unknown 1st test: Take organic unknown and put 5cm3 in a test tube and mix with 5cm3 water, or until the solution has properly mixed. Then add a few drops FeCl3 to the solution. The reaction which takes place will identify if there is phenol in the unknown. If the solution turns a violet colour then phenol is present, if there is no colour change then there is no phenol ring. 2nd test: Having ruled out phenol we move on to the next test, for a carboxylic acid. 5cm3 of the organic unknown should be placed in a boiling tube, with a side opening, with 5cm3 of water (or more as needed). Connect the boiling tube to a gas syringe in order to collect any gas which is evolved from the reaction. Set up a test tube with some limewater in it for later. Then the sodium hydrogencarbonate should be added, as a solid, and then put a bung in the top of the tube and let the gas syringe collect the gas. ...read more.

Middle

and the organic unknown. Put around 4cm3 2,4 DNPH in a test tube and drip the unknown into it, just a few drops. If a carbonyl group is present then we should see a yellow/orange precipitate in the tube. However, this test is not always reliable and so we should heat the compound gently for a few minutes and then leave it for 3mins to see if a precipitate is formed then. If there is still no precipitate formed then you have no carbonyl group, and this leaves only an alcohol and an ester group which may be present in the compound. If a precipitate is formed then go on to test 4 if not then go on to test 5. 4th test: This test will determine which carbonyl compound we have, either an aldehyde or a ketone. Firstly we take some of the unknown compound (approx. 5cm3) and put it in a test tube. ...read more.

Conclusion

If the compound is an alcohol then the reaction will do this: RCH2OH + [O] --> RCH2=O Then you can drop a few drops of this solution into 2,4 DNPH and if a precipitate is formed then you have a ketone or aldehyde, which means that the compound that you oxidised was an alcohol. If this test is negative and has no precipitate then you had an ester in the tube, as all other possibilities have been eliminated. You can confirm that the compound is an ester by the fruity smell, or y adding sodium to the solution, if there is a reaction then the unknown compound is an alcohol, if not then it is an ester as all other possibilities have been ruled out. Safety: Wear goggles throughout as you do not know what the unknown compound is. Take care when handling the concentrated H2SO4 and the NaCr2O7. Be careful not to get any of the 2,4 DNPH on your hands. Keep the Bunsen burner away from the organic compound as it may be flammable. ...read more.

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