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What is Lassaigne filtrate?

Author

Christopher Snyder

Updated on March 03, 2026

What is Lassaigne filtrate?

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, nitrogen, and sulphur, in an organic compound. The extract is filtered and the filtrate is called sodium extract or Lassaigne's extract.

Considering this, what is Lassaigne extract?

Theory: It is a general test for the detection of halogens, nitrogen and sulphur in an organic compound. The ionic compounds formed during the fusion are extracted in aqueous solution and can be detected by simple chemical tests. The extract is called sodium fusion extract or Lassaigne's extract.

Beside above, which element Cannot be detected by Lassaigne? Lassaigne's test for halogens involves treating the sodium extract with silver nitrate. A precipitate of silver chloride, bromide and iodide indicates the presence of halogen. Silver fluoride is soluble in water and does not precipitate and thus this method cannot be used for detection of fluorine.

Subsequently, one may also ask, how do you make Lassaigne solution?

Preparation of Sodium Fusion Extract (Lassaigne's Extract)

  1. Take a small piece of dry sodium in a fusion tube.
  2. Heat the tube slightly on a Bunsen burner so that the sodium melts to a shining globule.
  3. Add a pinch of the organic compound.
  4. Heat it slowly to start with so that the compound reacts with sodium metal.

How Sulphur is detected by sodium fusion extract?

Sulphur is a non – metallic chemical element with the symbol 'S'. Upon fusion with sodium metal, the sulphur atom in the organic compound is converted to ionic sodium sulphide, which can be extracted by boiling the fused mass with distilled water and is used for the detection of sulphur.

What is the theory of Lassaigne test?

It is a general test for the detection of halogens, nitrogen and sulphur in an organic compound. These elements are covalently bonded to the organic compounds. In order to detect them, these have to be converted into their ionic forms. This is done by fusing the organic compound with sodium metal.

Why sodium metal is used in Lassaigne test?

sodium used in lassaigne's test- because of electropostive nature and in order to convert covalent form to ionic form it is quite reactive . The halogens, nitrogen and sulphur are covalently bonded to the organic compounds. In order to detect them, the elements need to be converted into their ionic forms.

What is the test for Sulphur?

TEST FOR SULFUR
i) The appearance of a deep violet color upon addition of a few drops of sodium nitroprusside to SFE indicates the presence of sulfur. ii) Sulphur can also be detected by adding lead acetate to SFE, acidified with acetic acid. The formation of a black precipitate (PbS) indicates the presence of sulfur.

Is Sulphur organic or inorganic?

Inorganic sulphur includes pyritic and sulphate sulphur, present in coal as mineral matter. Some pyrites and sulphates also decompose to SO2 in certain reactions, as some organic sulphur compounds do.

Which compounds do not give Lassaigne test for nitrogen?

hydrazine and hydrazoic acid do not contain carbon. Thus these compounds cannot form NaCN on fusion with sodium. Hence, benzene diazonium chloride, hydrazine and hydrazoic acid cannot give Lassaigne's test of nitrogen.

Why do we use sodium extract?

The preparation of sodium carbonate extract affords a convenient method for bringing the anions of the mixture into solution which were otherwise insoluble with caution of salt. It removes the basic radical (usually coloured) which interferes in the usual tests of some of the acidic radicals.

How do you test for the presence of nitrogen?

In the Lassaigne's test for the detection of nitrogen in an organic compound, the appearance of a blue coloured compound is due to ferric ferrocyanide. In this test, sodium fusion extract is boiled with ferrous sulphate and then acidified with conc. sulphuric acid.

How do you test for nitrogen?

Upon fusion with sodium metal, the covalently bonded nitrogen is converted to ionic sodium cyanide, which can be extracted by boiling the fused mass with distilled water and is used for the detection of nitrogen.

Why sodium metal is used in element detection?

Halogens present in an organic compound forms sodium halide on fusion with sodium metal. These elements are covalently bonded to the organic compounds. In order to detect them, these have to be converted into their ionic forms. This is done by fusing the organic compound with sodium metal.

How do you detect nitrogen by Lassaigne's reagent?

Test for Nitrogen. The extract is boiled with FeSO4 and acidified with concentrated H2SO4. The appearance on Prussian blue colour indicates the presence of nitrogen.

Why freshly prepared FeSO4 is used in nitrogen test?

Why a freshly prepared solution of FeSO4 is used in Lassaigne's test for nitrogen ? Solution : An old sample of FeSO4 on keeping undergoes hydrolysis to form basic ferric sulphate. Te pale yellow colur of Fe+3 ions interferes with the light green colour usually obtained in Lassaigne's test.

What is fusion testing?

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, nitrogen, and sulphur, in an organic compound. The test involves heating the sample strongly with clean sodium metal, "fusing" it with the sample.

What is the test for halogens?

There are ways to test for halogens such as chlorine, bromine and iodine. One such procedure is the Beilstein Test. This test helps detect the presence of halogens in plastic.

How are halogens detected in an organic sample?

Halogen in an organic compound is detected by Carius method. A known mass of an organic compound is heated with fuming nitric acid in presence of silver nitrate contained in Carius tube. Carbon and hydrogen are oxidized to carbon dioxide and water. The halogen present forms silver halide, that is finally weighed.

What is the concept behind Beilstein test?

The Beilstein test is a simple qualitative chemical test for organic halides. It was developed by Friedrich Konrad Beilstein. A copper wire is cleaned and heated in a Bunsen burner flame to form a coating of copper(II) oxide. It is then dipped in the sample to be tested and once again heated in a flame.

Why is sodium metal dried up before fusion?

Why is sodium metal dried up before fusion ? Ans. It is done to avoid explosion due to of vapours of kerosene oil during heating. 9.

Why do you fuse sodium with organic compound?

Originally Answered: Why is organic compound fused with sodium metal before testing for foreign elements? The fusion with sodium metal is done to test for the presence of the halogens and sulphur in a given compound. On fusion the halogens are converted to the respective sodium halides, and sulphur to sodium sulphide.

Does aniline give Lassaigne test?

In Lassaigne;s test , aniline gives blue color with and acidic solution of FeSO4. Benzene sulfonic acid gives violet color with sodium nitroprusside.

Which compound gives Prussian blue with FeSO4?

Sodium cyanide is converted to sodium ferrocyanide on treating with ferrous sulphate. On further treating it with ferric chloride, a prussian blue complex, ferricferrocyanide is formed.

In which metal is used in Lassaignes test?

Why is sodium used in lassaigne's test? - Quora. Lassaigne's test is used to detect the presence of nitrogen, sulphur, chlorine, bromine and iodine in organic compounds.

What are extra elements?

The elements other than carbon, hydrogen and oxygen are known as extra elements. Detection of the extra elements is an important step in the investigation of an unknown organic compound. Thus, nitrogen in presence of carbon gets converted to cyanide ions, sulphur to sulphide ions and halogens to halide ions.

How would you detect the presence of Sulphur in the organic compound?

Nitrogen, sulphur, halogens and phosphorus present in an organic compound are detected by 'Lassaigne's test'. The elements present in the compound are converted from the covalent form into the ionic form by fusing the compound with sodium metal.

Can we use potassium in place of sodium in Lassaigne's test?

The extract is called sodium fusion extract or Lassaigne's extract. Theoretically, Potassium can be used instead of Sodium. However, because the tests are carried out in an aqueous solution it is difficult to control the explosive reaction when introducing Potassium.

Why only sodium is used in the preparation of Lassaigne filtrate?

sodium used in lassaigne's test- because of electropostive nature and in order to convert covalent form to ionic form it is quite reactive .

Can Potassium be used instead of sodium?

Potassium salts may even have a beneficial effect on your blood pressure because potassium is an antagonist of sodium. Potassium salts can be used in the same way as standard table salt and many people feel they do replace their need for salt.

How would you detect the presence of Hcons and halogens?

Elements like nitrogen, sulphur and halogens are bonded covalently in the organic compounds. In order to detect them, these have to be converted into their ionic forms. This is done by fusing the organic compound with sodium metal.

Is Sulphur harmful to humans?

Sulfur is low in toxicity to people. However, ingesting too much sulfur may cause a burning sensation or diarrhea. Breathing in sulfur dust can irritate the airways or cause coughing. If animals eat too much sulfur, it may be toxic and can be fatal.

What is the purpose of sodium fusion test?

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, nitrogen, and sulphur, in an organic compound. It was developed by J. L. Lassaigne.

Is Sulphur a metal?

Sulfur or sulphur is a chemical element with symbol S and atomic number 16. It is an abundant, multivalent NON METAL. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8.

Is sulfur a hazardous material?

General: Sulphur itself is essentially non-toxic. Molten sulphur is a hazardous material because of its high temperature (>122°C). Under certain conditions both heated and dry sulphur may evolve toxic hydrogen sulphide and sulphur dioxide gases.

Why is nitric acid added to sodium extract?

In the test of halogens from sodium extract, a small amount of dilute HNO3 is added. This is because in testing the halogen from the Lassigne's extract, it contains halogens. Nitric acid decomposes sodium cyanide and sodium halide. else, they precipitate in test and misguide the result.

Why is sodium extract alkaline in nature?

It is because in fusing the organic compounds with free sodium, some of the unreacted sodium react with distilled water, which is used to make the extract. Due to the formation of sodium hydroxide, the sodium extract becomes alkaline in nature.

How is sodium extract formed?

Preparation of Sodium Fusion Extract (Lassaigne's Extract)
  1. Take a small piece of dry sodium in a fusion tube.
  2. Heat the tube slightly on a Bunsen burner so that the sodium melts to a shining globule.
  3. Add a pinch of the organic compound.
  4. Heat it slowly to start with so that the compound reacts with sodium metal.

What does the dark Colour of sodium fusion extract indicate?

sulphide, which is black in colour, indicates the presence of sulphur in the compound. The sodium fusion extract is treated with sodium nitroprusside. Appearance of violet colour also indicates the presence of sulphur in the compound. Prussian colour is not formed due to the absence of free cyanide ions.

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