Keith Boldeau AS 11 Identification of organic Compounds

Procedure:

Alkene (C=C)

Potassium Manganate (VII) in alkaline solution is a weak oxidising agent. When an alkene is reacted with alkaline Potassium Manganate (VII) solution, the purple colour fades as alkene is oxidised.

. 5cm3 of each liquid is placed into test tubes.

2. 2 drops of Potassium Manganate (VII) is added to the test tube.

3. A purple to colourless change would be noticed in one of the test tubes, this is due to the oxidation of the alkene. The sample that gives the positive result will be removed from further tests and labelled Alkene.

Primary Alcohol ( C-OH)

. 5cm3 samples of the remaining five are placed in boiling tubes.

2. 2cm3 of aqueous potassium dichromate (VI) followed by 4cm3 of dilute sulphuric acid is added to each of the solutions.

3. Samples are gently boiled in water bath and observed for colour change. A water bath is used because some chemicals are potentially flammable.

An orange to green colour change would indicate the alcohol. This colour change is due to dichromate being reduced from Cr2O72- (orange) to (green) Cr3+ . As this is the only alcohol we can assume this is the primary alcohol. A silver mirror test can be carried out to verify it being a primary alcohol; with a positive test being formation of the silver mirror. The sample that gives the positive result will be removed from further tests and labelled Primary Alcohol.

Halogenoalkane (C-C-X)

. 5cm3 samples of the remaining 4 liquids are placed in boiling tubes.

2. They are then placed in water bath and heated; a water bath is used because some chemicals are potentially flammable.

3. 2cm3 sodium hydroxide is then added to each sample in order to hydrolyse the solution. 2cm3 nitric acid is then added to acidify the solution. Silver nitrate is added until no further change takes place.

A precipitate is formed in three of the sample solutions.

A white precipitate of Silver Chloride (Cl-) soluble in aqueous ammonia would indicate a chloroalkane.

A cream precipitate of Silver Bromide (Br-) soluble in concentrated ammonia would indicate a bromoalkane.

A yellow precipitate of Silver Iodide (I-) insoluble in ammonia would indicate an iodoalkane.

One of the sample liquids should have tested negative for each of the three tests carried out. This sample is the alkane.