What Is Lassaigne Test?

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In the expansive realm of analytical chemistry, various tests and methods serve as indispensable tools for identifying the presence of elements within compounds. Among these techniques, the Lassaigne Test stands out as a fundamental procedure employed to detect the presence of nitrogen, sulfur, and halogens in organic compounds. Let’s embark on a journey to understand the essence of the Lassaigne Test and its significance in analytical chemistry.

What Is Lassaigne Test?

The Lassaigne Test, named after the French chemist Jean Lassaigne, aims to identify the presence of elements like nitrogen, sulfur, and halogens (commonly chlorine, bromine, and iodine) in organic compounds. This test is particularly useful for detecting these elements when they exist in minute quantities that may not be easily identifiable through other means.

Methodology And Procedure

  • Preparation of Fusion Mixture: The organic compound is first mixed with solid sodium metal and then heated strongly. This process leads to the formation of sodium salts of the elements present in the compound.
  • Extraction with Water: The resulting mixture is dissolved in water and then subjected to extraction with dilute hydrochloric acid. This step facilitates the transfer of the formed salts into the aqueous phase.
  • Detection of Elements: The presence of the elements is determined through specific chemical tests. For instance, the nitrogen present in the compound is converted to sodium cyanide and then detected using tests for cyanide ions. Sulfur forms sodium sulfide, and halogens produce sodium halides, which are identifiable through various chemical reactions.

Significance In Analytical Chemistry

The Lassaigne Test serves as a crucial preliminary step in identifying the presence of these elements in organic compounds. While modern instrumental techniques like spectroscopy have largely replaced these classical methods for elemental analysis, the Lassaigne Test remains an essential learning tool in educational settings. It offers foundational knowledge and hands-on experience in elemental detection, laying the groundwork for understanding more sophisticated analytical techniques.

Limitations And Considerations

Despite its significance, the Lassaigne Test has limitations. It may not detect certain elements or compounds, and the process can be time-consuming and involve hazardous materials like sodium metal. Additionally, the test requires a skilled practitioner to perform it accurately and interpret the results effectively.


The Lassaigne Test, a cornerstone of classical analytical chemistry, remains a valuable technique in the exploration and identification of elemental constituents in organic compounds. Though surpassed by modern instrumental methods, its historical significance and educational value persist, providing a foundational understanding of elemental analysis.

While the Lassaigne Test may not be extensively used in contemporary analytical practice, its legacy endures as an essential part of the historical tapestry of chemical analysis, serving as a stepping stone for budding chemists and a testament to the evolution of scientific methodologies in uncovering the mysteries of chemical composition.


What Is Lassaigne Class 11?

What Is the Lassaigne’s Test? Nitrogen, sulphur, and halogens present in organic compounds are detected by Lassaigne’s test. Here, a small piece of Na metal is heated in a fusion tube with the organic compound. The principle is that, in doing so, Na converts all the elements present into ionic form.

What Is The Lassaigne’s Test For Chlorine Reaction?

During the preparation of Lassaigne’s extract, chlorine form the organic compound reacts with sodium to form sodium chloride. Sodium chloride gives a white precipitate of silver chloride with silver nitrate solution. The precipitate is soluble in ammonium hydroxide.

How Do You Prepare The Lassaigne Test?

Heat the tube slightly on a Bunsen burner so that the sodium melts to a shining globule. Add a pinch of the organic compound. Heat it slowly to start with so that the compound reacts with sodium metal. Now heat the tube strongly till it becomes red hot.

What Is The Colour Of Lassaigne Extract?

During the preparation of Lassaigne’s extract, sulphur from the organic compound reacts with sodium to form sodium sulphide. It gives a purple colour with sodium nitroprusside due to the formation of sodium thionitroprusside.

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What Is Lassaigne Test