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Aim: to detect the presence of unknown elements ( like N,S,P,X) in a given organic compound.
Materials Required:
given organic compound.
Sodium piece
ferrous sulphate
dil.sulphuric acid
dil.acetic acid
lead acetate
dil.nitric acid
silver nitrate
ignition tubes
tongs
bunsen burner
wire gauge
china dish
filter paper
funnel
glass rod
test tubes.
Theory:
The detection of extra elements in organic compounds is crucial in its investigation. Carbon is included in all organic molecules. Hydrogen is also found in most organic molecules (the few exceptions are the compounds such as CCl₄, CS₂, etc.). Other elements included in organic molecules include oxygen, nitrogen, sulfur, and halogens, in addition to carbon and hydrogen.Because virtually all organic substances include carbon and hydrogen, procedures to identify them are frequently unnecessary, and their existence may be presumed without testing. The tests for detecting nitrogen, sulfur, and halogens will be discussed here.
What is the Lassaigne’s Test, and how does it work ?
Lassaigne’s test can identify nitrogen, sulfur, and halogens organic molecules. A little bit of Na metal is heated with the organic compound in a fusion tube.The idea is that Na changes all of the elements present into ionic form.
Na + C + N → NaCN
2Na + S → Na₂S
Na + X → NaX ( X= Cl, Br, or I)
By boiling the fused mixture with distilled water, the produced ionic salts are removed. Sodium fusion extract is called Lassaigne’s Test.
Procedure:
Preparation of sodium Fusion Extract for Lassaigne's Test:
1. Firstly, take a little piece of sodium metal in the ignition tube and tape it a bit to make the metal settle down in the tube.
2. Heat the ignition tube until sodium metal becomes circular in shape
3. Put 1 pinch of compound in the tube and gently heat it .Heat it for 2 minutes continously.
4. Now, take 20 ml of distilled water in the china dish and place the tube in the china dish.
5. Do the same process for 4-5 times.
6. Crush the tube and heat it to let the water evaporate into half of the quantity.
7. Then filter it to remove the insoluble materials. Lassaigne's extract is the name given to filtrate.
NITROGEN TESTING:
Aim: To detect presence of nitrogen in given organic compound.
Materials required: Lassaigne extract, test tube, tongs, dil. sulphuric acid, ferrous sulphate.
Procedure:
take 1 ml Lassaigne extract in a test tube.
add one spatula ferrous sulphate in the test tube.
now, acidified the extract with dilute H₂SO₄ and heated it shortly.
let it be cool and observe the change of colour.
Observation:
The appearance of Prussian blue colour in test tube which indicates the presence of nitrogen.
The following reactions occurs:-
6CN⁻ + Fe²⁺→ [Fe(CN)₆]⁴⁻
H⁺+ Fe²⁺ → e⁻ + Fe³⁺
4Fe³⁺ + Fe(CN)₆⁴⁻ → Fe₄Fe(CN)₆.H₂O
Ferrous ions are oxidized to ferric ions with the assistance of the acid. The production of ferriferous cyanide indicates the presence of nitrogen.
SULFUR TESTING:
Materials required : Lassaigne extract, test tubes, tongs, dil. acetic acid, lead acetate
Procedure:
Take 1ml extract in test tube.
Add 1ml dil. acetic acid for acidification.
Now add lead acetate in the test tube.
Observation:
If black ppt form then given organic compound contains sulphur as extra elements.
HALOGEN TESTING:
Aim: To detect presence of halogen in given organic compound.
Materials required: Lassaigne extract, test tubes, tongs, dil. nitric acid, silver nitrate
Procedure:
Take 1ml Lassaigne extract in a test tube.
Add 1 ml dil. nitric acid in a test tube.
Now add little silver nitrate in the test tube.
Observation:
If a white ppt is formed in test tube then halogen is present as extra element in given organic compound.
COMBINED TEST FOR NITROGEN AND SULPHUR:
Aim: To detect presence of nitrogen and Sulphur together in given organic compound.
Materials required: Lassaigne extract, test tube, tongs, dil.hcl,fecl3
Procedure:
Take 1 ml Lassaigne extract in test tube.
Add 1 ml of dil. Hcl
Add fecl3 to the test tube.
Observe carefully.
Observation:
Observe blood red coloration in the test tube.
Results:
1. Prussian blue color is observed thus Presence of NITROGEN is confirmed.
2. Black ppt is observed thus presence of SULPHUR is confirmed.
3. Blood red colouration further confirms the presence of both nitrogen and sulphur.
Precautions:
1. Safety: Wear appropriate personal protective equipment, such as gloves and goggles, to protect yourself from any potential hazards.
2. Handling sodium: Sodium is a highly reactive metal that reacts violently with water. Handle sodium with caution, using dry forceps or spatula, and keep it away from moisture.
3. Fusion process: Carefully add a small amount of the organic compound to the fusion tube, followed by a small piece of sodium metal. Avoid adding excessive amounts of sodium, as it may lead to violent reactions.
4. Heating: Heat the fusion tube gently and gradually to avoid any sudden reactions or splattering. Use a Bunsen burner or a heating mantle for controlled heating
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