The sodium fusion test, or Lassaigne’s test, is used in elemental analysis for the qualitative determination of the presence of foreign elements, namely halogens. A method of testing for the presence of a halogen, nitrogen, or sulphur in an organic compound. A sample is heated in a test tube with a pellet of sodium. The hot. A drop of ferric chloride is added to this solution. A prussian-blue precipitate of ferric ferrocyanide, Fe4[Fe(CN)6]3 is formed. The formation of the prussian blue.

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Science and technology Chemistry GO. Sodium sulphide formed during the preparation of Lassaigne’s extract reacts with lead acetate to yield lead sulphide lassaige black precipitate. The mother liquor is decanted and the precipitate is treated with dilute aqueous ammonia solution.

HCl to precipitate the derivative of the primary amine. A crystalline precipitate indicates the presence of a carbonyl compound. Students understand various tests to detect the presence of nitrogen, sulphur and halogens in an organic compound.



The hydrogen chloride formed gives white fumes of ammonium chloride with ammonium hydroxide. It is then reduced to NTP conditions. In this test, the organic compound is fused with metallic sodium to convert these elements into water soluble sodium salt.

The alcoholic group can be detected by the following tests: If the precipitate is white and readily soluble in ammonia solution, chlorine is present; if it is pale yellow and difficulty soluble, bromine is present; if it yellow and insoluble, then iodine and bromine may be confirmed by the following test. Retrieved 31 Decemberfrom vlab. Publications Pages Publications Pages. Sign in with your library card.


Hydrogen is also present in most of the organic compounds, but there are few exceptions, such as: This halogen dissolves in carbon disulphide.

Bromine imparts orange colour and iodine imparts violet colour in lassxigne disulphide layer. If a colourless solution is obtained which gives an immediate and sustained positive test with starch indicate paper when only a little sodium nitrite solution has been added the compound is a tertiary aliphatic amine.

From the amount of barium sulphate, percentage of sulphur can be calculated. Neutral FeCl 3 i. The organic compound containing phosphorus is heated with fuming nitric acid.

Lassaigne Method | Determination of Molecular Mass-Askiitians

Reference books of Trst Chemistry. Do not translate text that appears unreliable or low-quality. Calculation of Empirical and Molecular Formula. If no precipitate forms immediately allow it is allowed to stand for minutes. This gives the relative number of atoms. Soluble in both ether and water. Show Summary Details Overview Lassaigne’s test.

Sodium fusion test

The most commonly occurring elements in organic compounds are carbon, hydrogen, oxygen, nitrogen, suphur and halogen elements. Preparation of Fehlings solution No. Students acquire the skill to prepare Lassaigne’s extract. Fusion solution is acidified with dil. Organic compound containing oxygen is heated with graphite and CO formed is quantitatively converted into CO 2 on reaction with I 2 O 5.


Separate based on Differences in the vaolalities of the component in aqueous solution: The molecular mass of an acid can be determined with the help of the following relationship. Science and technology — Chemistry.

Lssaigne iodine is present, an yellow precipitate insoluble in ammonium hydroxide solution is formed. When this solution is powered into less of water the colour of the aqueous solution is red, when excess of NaOH solution is added to the aqueous solution the red colour changes to blue or green.

Sodium bromide formed during the preparation of Lassaigne’s extract reacts with silver nitrate to form pale yellow precipitate of silver bromide, which tet sparingly soluble in ammonium hydroxide. To detect the halogens, nitrogen and sulphur in an organic compound. Physical methods for volatile compounds Victor Meyer’s method: This gives the simplest ratio of the various elements present.