Experiment 6

Aim: To detect the presence of extra elements (like N, S, P, X) in a given organic compound.

MATERIALS REQUIRED:

Given organic compound, Na 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, AgNO3 Solution, Conc. sulphuric acid, CHCl3 or CCl4 or CS2.

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 Lasseigne’s Test, and how does it work?

Lasseigne’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 what it’s called.

Halogen Testing:

For the halogens test, the sodium fusion extract is first acidified with HNO₃ and then treated with AgNO₃. The appearance of a white precipitate soluble in NH₄OH signifies the presence of Cl. A yellowish precipitate sparingly soluble in NH₄OH maybe Br and while a yellow precipitate insoluble in NH₄OH maybe I.

AgNO₃ + NaX → AgX ↓ + NaNO₃

 Confirmatory Test for Br and I (Layer Test): 

 Layer's test is the test that is used to detect in the presence of 'bromide' and 'iodide ions' in a compound. (To be performed if the AgNO₃ test is positive and doesn't show White precipitate. ) For the layer test, the sodium fusion extract is first treated with CHCl₃ or CCl₄ or CS₂ and then slowly along the sides of test tube Concentrated sulphuric acid is added. this gives an yellowish orangish colour layer Br is confirmed whereas if a violet colour is formed I is confirmed in the compound.

PROCEDURE:

Preparation of sodium Fusion Extract for Lassaigne's Test:

• 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.

• Heat the ignition tube until sodium metal  becomes circular in shape.

• Put 1 pinch of compound in the tube and gently heat it .Heat it for 2 minutes continously.

•  Now, take 20 ml of distilled water in the china dish and place the tube in the china dish. 

• Do the same process for 4-5 times.

• Crush the tube and heat it to let the water evaporate into half of the quantity.

• Then filter it to remove the insoluble materials. Lassaigne's extract is the name given to filtrate.

Points to be noted:

• white ppt formed can due to be chlorine, bromine and iodine 

• reactions to distinguish btw chlorine, bromine, iodine: 

• reaction with liq. ammonia solution:

a) test for chlorine:

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.

• add little silver nitrate in the test tube.

• then add liq.ammonia solution .

• if white ppt is soluble in liq. ammonia solution it means chlorine is present in given organic compound.

b) test for bromine:

materials required: Lassaigne extract, test tubes, tongs, dil. nitric acid, silver nitrate solution , liq. ammonia solution 

procedure: 

• taken 1ml Lassaigne extract in a test tube.

• added 1 ml dil. nitric acid in a test tube.

• added little silver nitrate in the test tube.

• then added liq. ammonia solution .

• if dirty white or light yellow ppt is formed and partially soluble in liq.ammonia, bromine may be there

confirmation test for bromine: 

test name: layer test

materials required: Lassaigne extract, CHCl₃ or CCl₄ or CS₂, conc. nitric acid , test tube

procedure: 

• take 2ml Lassaigne extract in the test tube.

• either add 2ml ccl4 or chloroform or CS2.

• along the side of test tube add conc. nitric acid.

what to observe:

if bromine is present Br2 gas forms, it will give orange colour in organic layer.

 c) test for iodine:

materials required: Lassaigne extract, test tubes, tongs, dil. nitric acid, silver nitrate solution , liq. ammonia solution.

procedure: 

• take 1ml Lassaigne extract in a test tube.

• add 1 ml dil. nitric acid in a test tube.

• add little silver nitrate in the test tube.

• then add liq. ammonia solution .

what to observe:

if yellow ppt forms which is insoluble in liq. ammonia solution, iodine is there.

confirmation test for iodine:

test name: layer test

materials required: Lassaigne extract, CHCl₃ or CCl₄ or CS₂, conc. nitric acid , test tube

procedure: 

• take 2ml Lassaigne extract in the test tube.

• either add 2ml ccl4 or chloroform or CS2.

• along the side of test tube add conc. nitric acid.

what to observe:

if iodine is present in form of I2, it will give violet colour in organic layer.

OBSERVATION:

violet colour was observed after the Layer's Test 

RESULT:

VIOLET colour is observed thus presence of IODINE is confirmed 

PRECAUTIONS:

Here are some precautions to consider when performing the Lasseigne's sodium fusion test:

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.