Determination of chemical components of a substance is called analysis of that substance. The analysis can be either Quantitative or Qualitative. Quantitative analysis involves determination of composition of a mixture, whereas, qualitative analysis involves identification of an unknown substance in a mixture. Identification of unknown substance during the qualitative analysis is done with the help of reagents. Alkalis are the important laboratory reagents. The most commonly used reagents are: sodium hydroxide which is a strong alkali and ammonium hydroxide which is a weak alkali. These alkalis react with the solution of metal salts to form precipitates of different coloured hydroxides, which may be soluble or insoluble in excess of these alkalis. Formation of precipitates of different coloured hydroxides helps in identifying the metal ion (cation) present in the salt. The salts on dissolving in water form salt solutions which are of different colours. The colour of the salt solution depends upon the cation and anion present in solution. Hot and concentrated alkalis react with certain metals like zinc, aluminium and form corresponding soluble salts and liberate hydrogen gas, which burns with pop sound. Most of the metal oxides are basic in nature, they dissolve in water forming hydroxides. These metal oxides and their hydroxides neutralise acids but do not react with bases. Some of the metallic oxides and hydroxides react with both acids and alkalis to form salt and water. Thus, they are amphoteric in nature.

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