aqueous ions Flashcards
what is a coordinate bond
Definition: A Coordinate Bond is a shared pair of electrons which have both come from the same atom.
what is a ligand
Definition: A Ligand is an ion or molecule with a lone pair of electrons which can form a coordinate bond with a transition metal ion.
what is a complex ion
A complex ion is a positive metal ion surrounded by ligands
what is the coordination number
Definition: The Coordination Number is the number of coordinate bonds a transition metal ion forms.
what are the 4 aqueous ions and colours do they form
[Fe(H2O)6]2+ -pale green solution
[Cu(H2O)6]2+ -blue solution
[Fe(H2O)6]3+ More acidic - purple solution ( may seem yellow/brown)
[Al(H2O)6]3+ More acidic - colourless solution
why are the 3+ ions more acidic
- Fe3+ is smaller and more highly charged than Fe2+
- So Fe3+ is more polarising
- This means Fe3+ strongly attracts the lone pair on the Oxygen of the water ligands.
- In turn this weakens the O-H bond strength.
- This means the Fe(III) complex more easily releases H+ ions making the solution acidic.
- The Fe(II) complex doesn’t release H+ ions.
equation which represents fe3+ acting as an acid
[Fe(H2O)6]3+ —> [Fe(H2O)5(OH)]2+ + H+
equation which represents al3+ acting as an acid
Al(H2O)6]3+ —-> [Al(H2O)5(OH)]2+ + H+
Reactions of [Fe(H2O)6]2+
With Na2CO3
[Fe(H2O)6]2+ + CO32- —-> FeCO3(s) + 6H2O
Observation: Green solution —-> green precipitate
Reactions of [Fe(H2O)6]2+
With NaOH
[Fe(H2O)6]2+ + 2OH- ——>Fe(H2O)4(OH)2 + 2H2O
Observation: Green solution —–> green precipitate
Reactions of [Fe(H2O)6]2+
With NH3
[Fe(H2O)6]2+ + 2NH3 —-> Fe(H2O)4(OH)2 + 2NH4+
Observation: Green solution —–> green precipitate
As before the green precipitate will turn brown on standing as the oxygen in the air oxidises it from Fe2+ to Fe3+.
This reaction is [Fe(H2O)4(OH)2] forms [Fe(H2O)3(OH)3]
Reactions of [Cu(H2O)6]2+
With Na2CO3
Cu(H2O)6]2+ + CO32- —-> CuCO3(s) + 6H2O
Observation: blue solution ——> blue green precipitate
Reactions of [Cu(H2O)6]2+
With NaOH
[Cu(H2O)6]2+ + 2OH- —–> Cu(H2O)4(OH)2 + 2H2O
Observation: Blue solution ——> blue precipitate
Reactions of [Cu(H2O)6]2+
With NH3
[Cu(H2O)6]2+ + 2NH3 —-> Cu(H2O)4(OH)2 + 2NH4+
Observation: Blue solution —–> blue precipitate
Reactions of [Cu(H2O)6]2+
With excess NH3
[Cu(H2O)6]2+ + 4NH3 —–>[Cu(H2O)2(NH3)4]2+ + 4H2O
Observation : Blue solution —-> deep blue solution
Cu(H2O)4(OH)2 + 4NH3 —–> [Cu(H2O)2(NH3)4]2+ + 2H2O + 2OH-
Observation: blue precipitate —–> deep blue solution