When a substance breaks down into at least two new other substances when heated.
Transition metal carbonates (transition metals with CO3 in them) break down when heated.
They break down into metal oxide and carbon dioxide, usually resulting in a colour change.
Copper(II) carbonate (green) --> Copper oxide (black) + Carbon dioxide
CuCO3 --> CuO + CO2
Can check CO2 by bubbling through limewater. If CO2 present, limewater goes cloudy.
Two solutions react and insoluble solid forms in solution.
Solid is said to precipitate out and solid is called precipitate.
Some soluble transition metal compounds react with sodium hydroxide to form insoluble hydroxide which precipitates out.
CuSO4 + 2NaOH --> Cu(OH)2 + Na2SO4
Copper(II) sulphate + Sodium hydroxide --> Copper(II) hydroxide + Sodium sulphate
FeSO4 + 2NaOH --> Fe(OH)2 + Na2SO4
Iron(II) sulphate + Sodium hydroxide --> Iron(II) hydroxide + Sodium sulphate
Fe2(SO4)3 + 6NaOH --> 2Fe(OH)3 + 3Na2SO4
Iron(III) sulphate + Sodium hydroxide --> Iron(III) hydroxide + Sodium sulphate
In ionic form: Cu2+ + 2OH- --> Cu(OH)2
Use Precipitation to Test Transition Metal Ions
Some insoluble transition metals have distinctive colours.
Copper(II) hydroxide is blue solid.
Iron(II) hydroxide is grey/green solid.
Iron(III) hydroxide is orange/brown solid.
You can use facts to test which transition metal ions a solution contains.
For example, if sodium hydroxide added to unknown soluble salt, orange/brown precipitate forms, so you know you have iron(III) hydroxide and Fe3+ ions in solution