Experiment 3

AIM:

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

MATERIALS REQUIRED:

• Given organic compound

• Na piece

• Ferrous sulphate 

• Dilute sulphuric acid

• Dilute acetic acid

• Lead acetate

• Dilute 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.

LASSAIGNE'S TEST

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 element's 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.

PREPARATION OF LASSAIGNE'S EXTRACT

In a fusion tube, place a little piece of dry sodium. Warm the line until it melts into a gleaming globule. A pinch of the organic substance should be added. First, heat it slowly to allow the chemical to react with sodium metal. Now bring it to a high temperature. Plunge the red hot tube into distilled water in a porcelain dish. Using a glass rod, crush the ingredients and bring to a boil. Filtration is used to remove the insoluble materials. Lassaigne’s extract is the name given to the filtrate.

USING EXTRACT FOR DETECTING PRESENCE OF UNKNOWN ELEMENTS

Sulfur testing

Aim: To detect presence of Sulphur in given organic compound.

Materials required: Lassaigne extract, test tubes, tongs, dilute acetic acid, lead acetate.

Procedure: 

• Take 1ml extract in test tube.

• Add 1ml dilute acetic acid for acidification.

• Now add lead acetate in the test tube.

Observation: No change in test tube.

Result: Given organic compound does not contain Sulphur as there is no formation of black ppt.

Halogens testing

Aim: To detect presence of halogen in given organic compound.

Materials required:  Lassaigne extract, test tubes, tongs, dilute nitric acid, silver nitrate.

Procedure:

• take 1ml Lassaigne extract in a test tube.

• Add 1 ml dilute nitic acid in a test tube.

• Now add little silver nitrate in the test tube.

Observation: No change in the test tube.

Nitrogen testing

Aim: To detect presence of nitrogen in given organic compound.

Materials required: Lassaigne extract, test tube, tongs, dilute sulphuric acid, ferrous sulphate.

Procedure:

• Take 1 ml lassaigne extract in a test tube.

• Add one spatula ferrous sulphate yin the test tube. 

• Now, acidified the extract with dilute H₂SO₄ and heated it shortly.

• Let it be cool and observe the change of color.

Observation: The appearance of Prussian blue color indicates the presence of nitrogen.

OBSERVATION:

RESULT:

Given organic compound contains nitrogen as extra element.

PRECAUTIONS:

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

•  Safety: Wear appropriate personal protective equipment, such as gloves and goggles, to protect yourself from any potential hazards.

•  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.

• 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.

• 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.