Question

Prior to testing for sulfur, nitrogen and halogens, the sodium fusion test is used. What is the effect of inadequate heating in the sodium fusion test?

Does it have something to do with making sure all the contents are completely charred and if so why?

Thank you :)

Answer 1

The sodium fusion test is also know as Lassaigne's test. It is used in the 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. The test involves heating the sample strongly with clean sodium metal, "fusing" it with the sample. The "fused" sample is plunged into the water, and the usual qualitative tests are performed on the resultant solution for the respective possible constituents. 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. This is done by fusing the organic compound with sodium metal. 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. When an organic compound is heated strongly with sodium, any halogens, nitrogen, and sulphur will be converted into inorganic sodium salts such as sodium halide (for halides), sodium cyanide (for nitrogen), sodium sulphide (for sulphur), and sodium thiocyanate (for sulphur and nitrogen).

In this process Charring (degradation) will not take place. The only conversion of an organic compound into inorganic compound will take place in the presence of sodium metal.