Standard level
Transition metals are the elements in the 'd' block of the periodic table. Their chemistry is conditioned by variable oxidation states and the ability to form coloured complex ions.
Background
Complex ions are ions in which the central metal atom is coordinated by groups of ligands, usually six or four. The colour of the complex depends on the oxidation state of the transition metal atom, the type and number of ligands.
In this experiment the students will observe the changes in colour of transition metal complex ions in solution as the ligands change.
- Concentrated hydrochloric acid provides chloride, Cl- ligands
- Concentrated ammonia solution provides ammonia ligands, NH3
- Sodium hydroxide solution provides hydroxide ligands, OH-.
Chemicals
- Cobalt(II) chloride, CoCl2.2H2O
- Copper(II) sulfate, CuSO4.5H2O
- Iron(II) sulfate, FeSO4.6H2O
- Hydrogen peroxide(aq), 10 vol
Apparatus
- Test-tubes and rack
- Wash-bottle
- Beaker, 100ml
- Stirring rod
- Spatula
- Prepare a rough solution of one of the salts by stirring 1 small spatula of compound into 50cm3 of water in a small beaker.
- Transfer 3 samples of 10cm3 of this solution into 3 test-tubes
- To the first test tube add a few drops of sodium hydroxide solution and shake