Qualitative analysis- Criteria of purity of organic compound

The qualitative analysis of an organic compound includes the detection of all the elements that are present in it. Carbon is a necessary constituent of an organic compound while hydrogen is nearly all time present. On heating the organic compound along with dry cupric oxide, carbon is oxidized to CO₂ and hydrogen to H₂O. CO₂ is detected by lime water that turns milky when H₂O is detected by anhydrous CuSo₄ (white) which turns it blue. This method is termed as copper oxide test.     

If the substance within examination is a volatile liquid or gas, the vapours are passed over heated copper oxide maintained in combustion tube and the gaseous products are tested as above.