Identification of an organic unknown.

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Identification of an organic unknown

(Skill P)


I am supplied with an unknown organic compound containing one of the following functional groups:

* Alcohol

* Aldehyde

* Ketone

* Carboxylic Acid

* Ester

* Phenol

Organic compounds have different functional groups and therefore differ from each other. They also react differently, I will use this method to determine the type of organic compound I have. I will conduct various experiments to narrow down the choices. After gathering the relevant information I will produce a flow chart.


There are many different chemical tests, which enable us to identify an unknown compound. The only thing known about the compound is that it contains one of the following functional groups: alcohol, aldehyde, ketone, carboxylic acid, phenol or ester. I devised a sequence of tests that would identify which of the groups the sample contains. Initially I worked out what tests there are for each functional group, and decided which one to use on the basis that each test should be dependent on the result of the previous test, which helped me to arrange the sequence.


Test for presence of alcohol:

The Cerric Nitrate Test


The alcohol complexes with the cerric nitrate ion

How to perform the test:

Three drops of the compound to be tested are added to 10 drops of an acidified cerric ammonium nitrate solution (a yellow solution).

Indications of a positive test:

The immediate formation of the red or red-brown colour indicates a positive test. Note that if the unknown is not soluble in water, two layers will be present. A red colour in either layer indicates a positive test.
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A negative test (left) and a positive test (right)

Test for presence of a carbonyl group:

The Brady's reagent (2, 4-dinitrophenylhydrazine (DNPH)) Test

Shows positive test for:

Aldehydes and ketones


Reacts with the carbonyl group of aldehydes and ketones. Condensation reactions are simply addition reactions which are immediately followed by an elimination process. In the case of carbonyl compounds water is normally eliminated.

How to perform the test:

Five drops of the compound to be tested are mixed with 5 drops of the DNPH ...

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