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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Ferric ions generated during the process react with ferrocyanide to form prussian blue precipitate of ferric ferrocyanide.

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. If no colour is observed the test is repeated as above but water substituted by absolute ethanol as solvent. On further treating it with ferric chloride, a prussian blue complex, ferricferrocyanide is formed.

Lassaigne’s test

A mixture of toluene may lassaiyne separated by extraction with dilute HCl; the aniline passes into the aqueous layer in the form of the salt aniline hydrochloride and may be recovered by neutralization. Sodium chloride gives a white precipitate of silver chloride with silver nitrate solution.

Acetyl chloride reacts vigorously with primary and secondary alcohols with the evolution of hydrogen chloride. This article may be expanded with text translated from the corresponding article in Spanish. Sodium nitroprusside test During the preparation of Lassaigne’s extract, sulphur from the organic compound reacts with sodium to form sodium sulphide. The above examples are simple applications of the fact that the various components full into different solubility groups.

In order to detect them, these have to be converted into their ionic forms.

The solution is then filtered and the halide is precipitated with silver nitrate solution. The filtrate is acidified with dil. Qualitative Analysis of Organic Compounds. In this test, the organic compound is fused with metallic sodium to convert these elements into water soluble sodium salt. Knowing the equivalent mass of silver salt, the equivalent mass of the acid can be obtained.


After qualitative analysis of elements, the next step in the determination of molecular formula of an organic compound is the estimation of various elements by mass, i. A known mass of the substance is vaporised above a mercury column in a barometric tube and the volume of the vapour formed is recorded. The halogens, nitrogen and sulphur are covalently bonded to the organic compounds. The presence of a halogen now in the form of a sodium halide is detected by precipitation with silver nitrate solution.

Halogens present in an organic compound forms sodium halide on fusion with sodium metal. Eudiometry is a direct method for determination of molecular formula of gaseous hydrocarbons without determining the percentage composition of various elements in it and without knowing the molecular weight of the hydrocarbon.

In this method the accurately weighed organic compound 0.


Empirical formula of a substance gives the simplest whole number ratio between the atoms of the various elements present in one molecule of the substance. Sign in to annotate. The sodium fusion testor Lassaigne’s testis used in elemental analysis for the qualitative determination of the presence of foreign elements, namely halogensnitrogenand sulphurin an organic compound.

Elemental nitrogen is converted into molecular nitrogen by a suitable chemical method and its voiume is changed to STP data. The precipitate is filtered OH and clear filtrate is used for the filtrate. Hydrogen is also present in most of the organic compounds, but there lassaigme few exceptions, such as: The solid is then treated with lassalgne again the sulphonamide from the primary amine is filtered OH. The ionic compounds formed during the fusion are extracted in aqueous solution and can be detected by simple chemical tests.


If iodine is present the organic phase becomes people in colour.

Lassaigne’s test – Oxford Reference

From the mass of magnesium pyro-phosphate, the percentage of phosphorus in the compound can be calculated. If bromine is present, an yellowish white precipitate sparingly soluble in ammonium hydroxide solution is formed.

The organic compound containing phosphorus is heated with fuming nitric acid.

Studying in Grade 6th to 12th? Detection of halogens 1. You must provide teet attribution in the edit summary by providing an interlanguage link to the source of your translation. Sodium metal test Acetyl chloride Cerric ammonium 1. This is done by fusing the organic compound with sodium metal.

Xpress Buy Xpress Buy. Neutral FeCl 3 i. When sodium bromide and sodium iodide in the Lassaigne’s extract is treated with chlorine water, the bromide and iodide oxidise to the corresponding halogens.

A drop of the given liquid or a crystal if solid is placed on a moist blue litmus paper. Don’t have an account? To the solution drops of freshly prepared dilute solution of disodium pentacyanonitroxyl ferrate Na 2 [Fe CN 5 NO] is added.

Students understand the chemical reactions and their balanced equations that takes place during each tdst. Thus, Equivalent mass of silver salt.

The extract is called sodium fusion extract or Lassaigne’s extract. Carbon disulphide test When sodium bromide and sodium iodide in the Lassaigne’s extract is treated with chlorine water, the bromide and iodide oxidise to the corresponding halogens. Our objective is to detect the presence of nitrogen, sulphur, chlorine, bromine and iodine in organic compounds by Lassaigne’s test. Elements other than these elements such as nitrogen, sulphur and halogens chlorine, bromine and iodine may also be present in organic compounds.

Sodium cyanide is converted to sodium ferrocyanide on treating with ferrous sulphate. Organic Chemistry Revision Notes.