Chemistry and Biotechnology

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Elemental Analysis

1Professor, School of Chemical Engineering, Chemistry and Biotechnology, Mapua Institute of Technology; 2Student, CHM146L-B31, School of Chemical Engineering, Chemistry and Biotechnology, Mapua Institute of Technology [pic]


Elemental analysis of organic compounds determine the elements present in them but they do not give the actual structure or the functional groups present. Since all organic compounds contain hydrogen and carbon, most tests consist of only the determination of oxygen, sulfur, nitrogen and halogens – elements that are most of the time the only ones involved in organic compounds. The experiment focused on the Sodium Fusion test, which tested for all elements except oxygen. In the test, the test compound is broken down into its elements, which then bond individually with sodium. The presence of sulfur was tested either with lead acetate or sodium nitroprusside. The presence of nitrogen was tested with ferrous ammonium sulfate and potassium fluoride. The presence of any halogen was tested by a flame test with copper wire and the identification of the exact halogen was done using silver nitrate. Careful experimentation was needed in order to avoid false positive and false negative results.

Keywords: elemental analysis, oxygen, sulfur, nitrogen, halogens, sodium fusion, lead acetate, sodium nitroprusside, flame test[pic] INTRODUCTION
Organic compounds are composed mainly of carbon and hydrogen, and in certain functional groups, oxygen, nitrogen, sulfur and halogens. When presented with an unknown organic compound, it is at times enough to determine the elements present in the compound and not the exact functional groups. The process in which the elements of a compound are determined is called elemental analysis. One of the tests done to conduct elemental analysis is the Sodium Fusion Test. In this experiment, sodium fusion test is used in elemental analysis of qualitative determination of elemental halogens, sulphur and nitrogen in a sample. Sodium is a very strong reducing agent that will able to break up the organic compounds carbon atom chain. It also will convert the atoms which are covalently bonded to the carbon chain to inorganic ions. The elements are detected by sodium fusion test. The organic compound is fused with metallic sodium to convert these elements into ionic mixture which dissolved in water and the filtrate is used to perform the tests.

The sodium fusion test, in some texts known as the Lassaigne’s test, was developed by the French chemist, Jean Louis Lassaigne in the 1800’s. It is a general test performed in order to determine the presence of nitrogen, sulfur and halogens. The principle behind the test is the breakdown of the compound into its elements at high temperatures. The breakdown of a compound into its elements is possible for organic compounds as they do not dissociate and form ions when dissolved in a liquid unlike salts and other ionic compounds. These elements then fuse with sodium. These sodium compounds are then the ones tested with different solutions that reveal the presence or absence of the above elements. A limitation of this test is that it cannot test for the presence of oxygen, however, the presence of oxygen can easily be determined through the determination of the actual functional groups in the compound. 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. 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 (Wikipedia, 2012.) When an organic compound is heated strongly with sodium, any halogens, nitrogen, and sulfur will be converted...
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