Identification of Unknown Organic Compound
This aim of this coursework is to plan and outline a sequence of
simple chemical tests that can be used to identify unknown organic
These unknown compounds contain one of the following functional
groups: Alkenes, Tertiary Alcohol, Aldehyde, Ketone, carboxylic acid,
Primary Alcohol, Ester and Phenol.
The tests, observations, and inferences will be tabulated and then the
risk analysis/safety precautions
will be tabulated as well, followed
by a flow chart.. the flow chart will be drawn separately from the
test, because drawing a flowchart that includes,, tests, observation
and inferences will be too rough.
Reagents and Apparatus
Test tubes/Test tube racks
Acidified Potassium Dichromate (VI) (K2Cr2O7)
5% Aqueous Sodium hydrogen carbonate (NaHCO3)
Water Cooled condenser
Clamp and stand
20ml - 400ml Beakers
Phosphorous Pentachloride (PCl5)
Sodium metal (Na)
Jones’s reagent (CrO3-H2SO4 in H2O)
Bunsen burner/heating Mantle
1 ml of 0.5 mols hydroxylamine hydrochloride
Sodium Hydroxide (NaOH)
Hydrochloric Acid (HCl)
Lucas reagent [ZnCl2 - conc. HCl]
For Hydroxyl groups, OH in Alcohols, Phenols and Carboxylic acid
Pour 1cm3 of sample into test tube in fume cupboard (making sure that
the test tube is in a rack).
Carefully add a spatula of PCl5 bit by bit.
Keep product Dry
If positive, steamy white fumes will be given off.
Hydroxyl group present, could be Primary alcohol, Tertiary Alchohol,
Phenol or Carboxylic acid
Ethanoic acid test
Test for all Alcohols
Pour 2cm3 of H into test tube; add equal volume of ethanoic acid. Add
10 drops of H2SO4 and the warm gently.
Pour mixture into 400ml beaker containing 200ml water.
A Sweet smell is given off
Alcohols present, could be primary or Tertiary. The Alchohol was
oxidised to and ester.
Test for Primary Alchohols using Jones’s reagent
(CrO3-H2SO4 in H2O)
In a test tube, place 1 ml of acetone in a test tube and dissolve one
drop of the unknown compound
Add one drop of Jones’s reagent and then shake the test tube to mix
Primary and secondary alcohols react within two seconds. There is
colour change form orange to green or blue-green, product is a
Primary alcohol is fully oxidised to acid,
No reaction for Tertiary Alchohol.
Primary Alchohol Present and Confirmed.
Label Test tube “Alchohols”
Test for Tertiary Alchohol using Lucas reagent
[ZnCl2 - conc. HCl]
To 1 ml of the unknown compound in a test tube add 6 mls of Lucas'
reagent at room temperature. Close the tube with a cork, shake
properly and then allow to stand.
Very fast reaction and droplets of alkyl chloride formed almost
For Primary alcohols there is no reaction (except allyl alcohol -
droplets which are formed after 7 minutes).
Therefore tertiary Alcohol is present and Confirmed.
Label test tube Tertiary Alchohol
pH of aqueous solution
Test the pH of the unknown compound using universal indicator
Carboxylic acid around pH 3-4
Phenol around pH 5-6
Phenol and carboxylic acids again confirmed present.
Acid test for carboxylic groups
Add a spatula of NaHCO3 to aqueous unknown compound
A gas is given off. Gas turns lime water milky, ( Gas given off is
Carboxylic acid present and confirmed as this test is negative for
Phenols and Alchohols.
Label Test tube Carboxylic Acid
This is the test for Phenols
Dissolve 0.50g of unknown compound in water, add aqueous solution of
iron(III) chloride drop-wise
There is colour change.
Violet colour for phenol,
Red colour for carboxylic acids
Phenol present and confirmed
Label Test tube Phenol
This is a test for carbonyls ( Aldehydes and Ketones)
Add a few drops of a solution of 2,4-DNP t o the unknown compound
Label product Carbonyl
A yellow or orange precipitate is produced.
No Precipitate is produced with Carboxylic acid, phenol or esters.
Therefore carbonyls(Aldehyde and Ketone) present
Confirmation of Aldehyde using Tollens Reagent
Add 2 - 3 drops of the unknown compound in methanol to 2 - 3 mL of
Tollen's reagent contained in a very clean test tube. Warm gently in a
A silver mirror forms on the side of the test tube from the colourless
Silver Ion is reduced to silver metal.
Reaction is negative with Ketone
Therefore Aldehyde Present and Confirmed.
Label test tube Aldehyde.
Confirmation of Presence of Ketone
Recrystallise the product labelled Carbonyl (from Test No. 8 ).
Determine its melting point, and then compare against a known ketone
Melting point matches that of a known ketone
Ketone present and Confirmed.
Label test tube as Ketone
To the unknown compound add bromine water drop-wise until the bromine
Bromine water is decolourised from brown to colourless
Phenol will form a white ppt with bromine water, but a colourless
solution depicts presence of Alkenes.
Alkenes present and confirmed.
Label test tube as Alkenes
Hydroxamic acid test for Identifying esters
In a test tube, mix 1 drop of unknown compound with 1 ml of 0.5 mols
hydroxylamine hydrochloride in 95% ethanol and add 0.2 ml of 6 mols
aqueous sodium hydroxide. Heat the mixture until it boils. On cooling,
add 2 ml of hydrochloric acid. If the solution is cloudy, add 2 mL of
95% ethanol. Add I drop of 5% iron (III) chloride. Observe colour
A positive test will be a distinct burgundy or magenta colour
Esters react with hydroxylamine in the presence of sodium hydroxide to
form the sodium salt of the corresponding hydroxamic acid. On
acidification and addition of ferric chloride the magenta-coloured
iron (III) complex of the hydroxamic acid is formed.
Therefore Ester is present and confirmed.
Alchohols – (Ethanol)
Causes skin and eye irritation
Harmful by Inhalation
Avoid contact with skin and eyes. Wear eye protection; wash with cold
water in the event of contact.
Avoid contact with open fire, take car while heating/refluxing, if
possible use heating mantle instead of Bunsen burner.
Avoid Inhaling gas
May act as Irritant
Wear safety glasses
Ensure there is adequate ventilation
Liquid can cause damage to skin and eyes
See safety precautions on alchohols
Always use the fume cupboard
After the test with Tollens reagent, pour the contents of the test
tube into a sink and wash the test tube with dilute nitric acid. Any
silver fulminate present, which is highly explosive when dry, will be
* Proper care should be taken when handling glass wares
Here are some resources that I used for this coursework.
Make the Grades Chemistry
By George Facer
OCR Chemistry 2
Pages 7,16,21-31 &50