Identification of an organic compound - page 1
Keywords: Identification of an organic compound gcse a level chemisrtry
By Mehak on 10/03/2011
Level: A Level (Year 13)
Page Number: 1 of 3 pages: 1 2 3
IDENTIFICATION OF AN ORGANIC COMPOUND
INTRODUCTION:
The aim for this investigation is to identify an unknown organic compound containing one of the following functional groups:
Alkene
Primary alcohol
Tertiary alcohol
Aldehyde
Carboxylic acid
Ketone
Phenol
Ester
To indentify I will take each of the functional group and test to see if the functional group is present in a unknown organic compound.
Safety:
Safety goggles must be worn at all times in order to protect eyes from splashing chemicals or hot water.
Empty the table before start doing an experiment so that no-one has any kind of accident-such as handling the glass apparatus because they are breakable and cause serious injure.
Lab coat must be worn to avoid chemicals splash on your clothes
Chemical equipment Hazards Precautions
Bromine water Irritating ,toxic and high flammable Burn to skin and eyes
Potassium dichromate corrosive Severe eye damage
Zinc chloride corrosive Redness and pain
Hydrochloric acid Extremely corrosive Contact with skin cause serious permanent damage.
2, 4 dinitrophenylhydrazine Irritant Red skin, feel itchy
Sodium hydroxide Corrosive Contact with skin causes irritation or severe burn.
Silver nitrate Poisonous Contact with skin leaves silver stains on skin.
Hydroxylamine hydrochloride Corrosive, causes burn Causes skin irritation
Potassium hydroxide Corrosive Causes severe eye and skin burns
Iron (III) chloride Corrosive Causes severe eye and skin burns
Apparatus:
Test tubes and a test tube holder
Pipettes
Spatula
Water bath
Potassium dichromate
2,4 dinitrophenylhydrazine
Tollens reagent
Sodium Hydrogen Carbonate
Limewater
Sodium Metal
Filter paper
Iron(III)Chloride (FeCl3)
Safety Glasses
Gloves
Lab coat
2, 4-dinitrophenylhydrazine (DNPH) Test (for presence of a carbonyl group)
Carbonyl compounds:
The carbonyl compounds is the presence of carbon - oxygen double bonds C=O. The functional group on aldehydes and ketones is a carbonyl group.
Carbonyl compounds can be tested with a reagent of 2, 4 dinitrophenylhydrazine. A positive test will show yellow precipitate.
Method:
Add 5 drops of unknown compound into the test tube
Add 5 drops of the DNPH reagent
Shake the tube gently
If the solution turns into a yellow or orange precipitate then a carbonyl compound is present.
Equation:
Orange 2, 4-dinitrophenylhydrazine forms with the 2-propanone indicating the presence of an aldehyde or ketone.
(http://jchemed.chem.wisc.edu/jcesoft/cca/CCA5/MAIN/1ORGANIC/ORG12/TRAM12/B/0380011/MOVIE.HTM)
The reaction is a condensation reaction as water is been eliminated in the formation of the carbon-nitrogen double bond in a hydrazone.
Tollens reagent test (to distinguish between Aldehyde and Ketones):
Method:
Put 2cm3 of silver nitrate in a test tube, add 3-4 drops of sodium hydroxide. This shows the gray precipitate of silver oxide
Add few drops of ammonia solution and shake the test tube gently after each drop until the precipitate just dissolves.
Rinse the test tube with sodium hydroxide and take 1 cm3 of Tollens reagent, tilt the test tube and add the drops of unknown compound, letting
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