Identification of an organic unknown

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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. If no gas is evolved then you do not have a carboxylic acid and should ignore the rest of this experiment and move onto test three. After the reaction has completed squeeze the tubing at the end of the gas tube and then disconnect the rubber tube from the boiling tube. Then move the end of the rubber tube into the limewater and press the gas syringe to allow the gas to bubble through the limewater. You should observe a precipitate in the solution and it will turn cloudy. This is what is happening in this experiment:

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RCOOH + NaHCO3 →RCOONa(aq) + CO2(g) +H2O(l) 

The gas here is the carbon dioxide, which is then bubbled through the limewater in this reaction:

Ca(OH)2 + CO2 →CaCO3(s) + H2O

3rd Test:

This test shows if a carbonyl group is present in the unknown compound. For this test we use 2,4 dinitrophenylhydrazine (2,4 DNPH) 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 ...

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