Transition metal hydroxides are insoluble in water.
If a solution of any soluble transition metal compound is mixed with sodium hydroxide solution then we get a displacement reaction. The sodium is the more reactive metal, and displaces the transition metal from its compound. The transition metal hydroxide is produced as a result. As this is insoluble in water it appears as a solid in the liquid. A solid produced in a liquid in this way is called a precipitate.
The colour of the precipitate indicates which transition metal ion was in the initial solution.
|Transition metal ions in solution||Precipitate formed when mixed with sodium hydroxide solution||Colour of the precipitate|
You need to be able to construct the balanced symbol equations for the thermal decomposition reactions and the precipitation reactions described in this section.
FeCO3 → FeO + CO2
CuCO3 → CuO + CO2
MnCO3 → MnO + CO2
ZnCO3 → ZnO + CO2
Cu2+ + 2OH- → Cu(OH)2
Fe2+ + 2OH- → Fe(OH)2
Fe3+ + 3OH- → Fe(OH)3
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