Qualitative inorganic analysis

Classical qualitative inorganic analysis is a method of analytical chemistry which seeks to find the elemental composition of inorganic compounds. It is mainly focused on detecting ions in an aqueous solution, therefore materials in other forms may need to be brought to this state before using standard methods. The solution is then treated with various reagents to test for reactions characteristic of certain ions, which may cause color change, precipitation and other visible changes.[1]

Qualitative inorganic analysis is that branch or method of analytical chemistry which seeks to establish the elemental composition of inorganic compounds through various reagents.

Physical appearance of inorganic salts

Salt Colour
1 MnO, MnO2, FeO, CuO, Co3O4, Ni2O3; sulfides of Ag+, Cu+, Cu2+, Ni2+, Fe2+, Co2+, Pb2+, Hg2+, Bi3+, Hg, BiI3, Bi(s), Cu(SCN)2, Sb(s), Hg2O(s), Cu[C(=NH)S]2(s) Black
2 Hydrated Cu2+ salts, Co[Hg(SCN)4](s), Blue
3 HgO, HgI2, Pb3O4, Hg2CrO4(s), Ag2CrO4(s), Red
4 Cr3+, Ni2+, hydrated Fe2+ salts, Hg2I2(s), Cu(C7H6O2N)2(s), CuHAsO3(s), Green
5 Hydrated Mn2+ salts Light Pink
6 KO2, K2Cr2O7, Sb2S3, Ferrocyanide, HgO, Sb2S3(s), Sb2S5(s) Orange
7 Hydrated Co2+ salts Reddish Pink
8 Chromates, AgBr, As2S3, AgI, PbI2, CdS, PbCrO4(s), Hg2CO3(s), Ag3PO4(s), Bi(C6H3O3)(s), Cu(CN)2(s), Ag3AsO3(s), (NH3)3[As(Mo3O10)4](s), [SbI6]3-(aq), Yellow
9 CdO, Fe2O3, PbO2, CuCrO4, Ag2O(s), Ag3AsO4(s), Brown
10 PbCl2(s), Pb(OH)2(s), PbSO4(s), PbSO3(s), Pb3(PO4)2(s), Pb(CN)2(s), Hg2Cl2(s), Hg2HPO4(s), Al(OH)3(s), AgCl(s), AgCN(s), Ag2CO3(s), Bi(OH)2NO3(s), Bi(OH)3(s), CuI(s), Cd(OH)2(s), Cd(CN)2(s), MgNH4Also4(s), SbO.Cl(s), Sb2O3(s), White

The sodium carbonate test (not to be confused with sodium carbonate extract test) is used to distinguish between some common metal ions, which are precipitated as their respective carbonates. The test can distinguish between copper (Cu), iron (Fe), and calcium (Ca), zinc (Zn) or lead (Pb). Sodium carbonate solution is added to the salt of the metal. A blue precipitate indicates Cu2+ ion. A dirty green precipitate indicates Fe2+ ion. A yellow-brown precipitate indicates Fe3+ ion. A white precipitate indicates Ca2+, Zn2+, or Pb2+ ion. The compounds formed are, respectively, copper(II) carbonate, iron(II) carbonate, iron(III) oxide, calcium carbonate, zinc carbonate, and lead(II) carbonate. This test is used to precipitate the ion present as almost all carbonates are insoluble. While this test is useful for telling these cations apart, it fails if other ions are present, because most metal carbonates are insoluble and will precipitate. In addition, calcium, zinc, and lead ions all produce white precipitates with carbonate, making it difficult to distinguish between them. Instead of sodium carbonate, sodium hydroxide may be added, this gives nearly the same colours, except that lead and zinc hydroxides are soluble in excess alkali, and can hence be distinguished from calcium. See qualitative inorganic analysis for the complete sequence of tests used for qualitative cation analysis.

See also


  1. E. J. King "Qualitative Analysis and Electrolytic Solutions" 1959, Harcourt, Brace, and World, New York.
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