- Qualitative analysis of organic compounds: Analysis involving detection of all elements present in an organic compound.
- Detection of carbon and hydrogen by the copper oxide test
- Qualitative analysis (Detection of elements):
- Detection of nitrogen, halogen and sulphur by Lassaigne’s test
- Detection of carbon and hydrogen: Carbon and hydrogen are detected by heating the compound with copper (II) oxide. Carbon present in the compound is oxidised to carbon dioxide and hydrogen to water. Carbon dioxide is tested with lime water. Carbon dioxide makes lime water milky and develops turbidity. Water is tested with anhydrous copper sulphate, which becomes blue on absorbing moisture.
- Detection of nitrogen: The sodium fusion extract (prepared by boiling fused mass of the compound and sodium metal in distilled water) is boiled with FeSO4 (iron (II) sulphate) and then acidified with concentrated sulphuric acid. The formation of a Prussian blue colour confirms the presence of nitrogen.
- Detection of sulphur: Two tests can be performed for the detection of sulphur.
- a. On adding lead acetate to acidified sodium fusion extract, the formation of a black precipitate confirms the presence of sulphur.
- b. On adding sodium nitroprusside to acidified sodium fusion extract, the appearance of violet colour indicates the presence of sulphur.
- Detection of halogens: On adding a silver nitrate solution to sodium fusion extract acidified with nitric acid, a white precipitate (soluble in ammonium hydroxide) shows the presence of chlorine, a yellowish precipitate (sparingly soluble in ammonium hydroxide) shows the presence of bromine and a yellow precipitate (insoluble in ammonium hydroxide) shows the presence of iodine.
- Detection of phosphorus: The compound containing phosphorus is heated with an oxidising agent (sodium peroxide) which oxidises phosphorus to phosphate. The solution is boiled with nitric acid and then treated with ammonium molybdate. A yellow colouration or precipitate indicates the presence of phosphorus.
- Qualitative Analysis of Inorganic Compounds:
Identification of acidic radicals (anions):
Identification of basic radicals (cations):