This is an investigation to identify some compounds containing oxygen AimThis experiment is to identify the chemical by use of their functional group in simple reactions

CH3COCH3 + C6H3(NO2)2N2H3                            C6H3(NO2)2NHN=C(CH3)2 +H2O

Warm acidified dichromate oxidises alcohols, primary alcohols are oxidised to an aldehyde then to a carboxylic acid if there is enough dichromate to oxidise the aldehyde, so if the Tollens reagent is added the aldehyde is oxidised to a carboxylic acid in a similar way but metallic silver is also produced giving a positive result. Secondary alcohols are oxidised to a keytone (Propanone in this case), so will not be affected by the Tollens reagent because keytone have no reducing ability.

CH3CH(OH)CH3 + [O]                     CH3COCH3 + H2O

When a magnesium strip is added to carboxylic acid hydrogen is evolved causing effervescence.

Mg + 2C2H5COOH                       (C2H5COO)2Mg + H2

Esters are used as artificial flavourings so they smell sweet and fruity; the ester in this case is no different so a simple test would be to have a smell at it.

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Apparatus

• Chemical

• Magnesium
• Acidified Potassium dichromate
• Sulphuric acid
• Ammonia
• Silver nitrate
• 2,4-dinitrophenylhydrozine

• Equipment

• Quick fit apparatus for quick fit
• Plastic pipette
• Test tubes
• Beakers
• Electric hot plate heater
• Bunsen
• Heat proof mat

Safety

Some of the chemicals used in the investigation are flammable so use of reflux apparatus prevents the flame of the Bunsen from being in contact with the compounds

Use of electric heaters to heat open containers should be used due to the risk presented by the flammable chemicals around the work area.

Method

• Identifying the Propanal

1. Take a 10cm3 sample of each of the 6 compound and put each sample in a separate test tube.
2. Carefully add ammonia solution to silver nitrate until the initial grey precipitate just disappears (this forms ammoniacal silver nitrate) add a few drops of sulphuric acid.
3. Add 2-3cm3 of the ammoniacal silver nitrate to each test tube
4. Wait until one of the test tubes forms a silver “mirror” on the edge of the tube.
5. label the bottle which the sample came from ‘Propanal’

• Identifying the Propanone

6. Take a 10cm3 sample of each of the 5 compound and put each sample in a separate test tube.
7. Add a small amount of acidified 2,4-dinitrophenylhydrazine dissolved in methanol, a yellow/orange precipitate forms in only 1 of the 5 tubes
8. Label the bottle which the 1 sample came from ‘Propanone’

• Identifying the Propan-1-ol and Propan-2-ol

9. Take a 10cm3 sample of each of the 4 compound and put each sample in a separate test tube.
10. Setup quick fit apparatus for heating under reflux
11. Add the first sample with acidified potassium dichromate into a pear shaped flask and heat under reflux
12. If the sample changes colour from orange to green

1. pour the sample back into the test tube and add some ammoniacal silver nitrate
2. if the sample then forms a silver mirror then label the bottle which the sample came from ‘1º’ if the sample does not form a silver mirror label the bottle which the sample came from ‘2º’

13. if the sample does not change colour repeat steps 3 and 4 for each of the other samples

• Identifying Propanoic acid

14. Take a 10cm3 sample of each of the 2 compound and put each sample in a separate test tube.
15. Add a magnesium strip to the 2 test tubes if effervesance occurs label the bottle which the sample came from ‘Propanoic acid’

• Identifying Methyl ethanoate

16. smell the final bottle
17. if it smells sweet label the final ‘methyl ethanoate’

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