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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During the preparation of Lassaigne’s extract, chlorine form the organic compound reacts with sodium to form sodium chloride. Calculation of Empirical and Molecular Formula Empirical formula: If the base is mono-acidic, the formula lasasigne the salt will be.

Cyanide and sulphide ions both interfere with this test for halide by forming silver cyanide and silver sulphide precipitates. Sodium nitroprusside test During the preparation of Lassaigne’s extract, sulphur from passaigne organic compound reacts with sodium to form sodium sulphide.

A crystalline precipitate indicates the presence of a carbonyl compound. A sample is heated in a test tube with a pellet of sodium. A shining mirror confirms the presence of the aldehyde. The mixture is treated with sufficient dilute NaOH solution to transform the acid into sodium acetate and distilling the aqueous mixture.

The organic compound containing phosphorus is heated with fuming nitric acid. The filtered fusion solution dil.


Science and technology Chemistry GO. They can be separated by treatment with dil. They can be separated by adding sufficient dilute H 2 SO 4 to neutralise the base steam distillation will remove the alcohol.

Lassaigne’s test – Oxford Reference

The most commonly occurring elements in organic compounds are carbon, hydrogen, oxygen, nitrogen, suphur and halogen elements. The test tube is warmed until the pallets dissolve. The actual method used involves the following steps, A known volume of the gaseous hydrocarbon is mixed with an excess known or unknown volume of oxygen in the eudiometer tube kept in a trough of mercury. This gives the relative number of atoms.

Soluble in water but insoluble in ether. The various methods commonly employed for the estimation of principal elements are discussed in the table.


Method and its principle. Sodium chloride gives a white precipitate of silver chloride with silver nitrate solution. Halogens i Carius method: 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.

Lassxigne 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.

Detection of Nitrogen If nitrogen is present in the compound, the Lassaigne’s extract would contain sodium cyanide formed during fusion. By using this site, you agree to the Terms of Use and Privacy Policy.


Don’t have an account? The filtered alkaline solution resulting from the action of water upon the sodium fusion is treated iron II sulphate and thus forms sodium hexayanoterrate II. A sweet, fruity smell of an ester confirms the presence of ester. DearPreparing for entrance exams? Two solutions separately keeped in tightly stoppered bottles and mixed exactly equal volumes immediately before use. If a transient or permanent colouration usually purple, blue or green other than yellow or orange is observed, the substance probably a phenol or an enol.

If the Lassaigne’s extract containing excess of sodium metal, sodium cyanide and sulphides are formed instead of sodium thiocyanate. A small amount of the acid with two parts of absolute ethanol lqssaigne one pare of concentrated sulphuric acid is warmed for 2 minutes.

Elevation in boiling point of the solvent determined experimentally. Science and technology — Chemistry. MOB20 View Course list. Sodium halide extracted with water lassajgne be easily identified by adding silver nitrate solution after acidifying with dil. If the colour changes to red, phenolic group may be present. In this method, a known weight of organic compound is heated with pure and dry cupric oxide in a steam of pure and dry oxygen, when carbon is oxidised to carbon dioxide while hydrogen is oxidised to water.