Elements in Carbon Compounds

Detection of carbon and hydrogen. The detection of carbon and hydrogen is based upon the formation of carbon dioxide and water when compounds containing these elements are heated with copper oxide. The formation of carbon dioxide is detected by passing the gases produced through a solution of barium or calcium hydroxide, whereby barium or calcium carbonate is precipitated. The formation of water is detected by the appearance of droplets in the upper (cool) part of the ignition tube. 

Detection of halogens. Very few organic compounds contain halogen atoms which form halide ions in aqueous solutions and so can be detected by the addition of silver ion. It is necessary, therefore, to convert the organic halogen to a metallic halide by fusion with metallic sodium or calcium oxide. By such decomposition nitrogen and sulfur, if present, form ions which can be detected by the usual methods of qualitative inorganic analysis. 

The presence of halogens can be demonstrated by the Beilstein Test. A small amount of the sample is placed on a copper wire and burned in the Bunsen flame. The copper halide which forms imparts a green color to the flame. This test, though sensitive, must be conflrmed through fusion and detection by means of silver halide. 

Sodium fusion for detection of halogens, nitrogen, sulfur. When an organic compound is heated with metallic sodium, decomposition occurs. Free carbon is deposited, and some carbon monoxide and dioxide are formed. The halogens forms halides (NaCl, NaBr, and Nal). Nitrogen in presence of carbon and sodium gives sodium cyanide, NaCN sulfur forms sodium sulflde, NajS. 

The residue obtained by fusion is warmed with a small amount of alcohol to decompose the unreacted metalhc sodium and is extracted with water. Portions of the filtered alkaline solution are used for the detection of hahde, cyanide, and sulfide ions. 

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