Reactions of aqueous ions Flashcards
What is meant by enthalpy of hydration?
- standard enthalpy change
- when one mole of gaseous ions
- covered into one mole of aqueous ions
enthalpy of hydration is…
- always exothermic
- bonds made with water molecules
What is a co-ordinate bond?
- shared pair of electrons
- that have come from the same atom
What is a ligand?
- ion/molecule with lone pair of electrons
- forms co-ordinate bond with transition metal ion
What is a complex ion?
central atom/ion surrounded by ligands
What is the co-ordination number?
number of co-ordinate bonds formed by transition metal ion
What are the 4 hexa aqua ions?
[Fe(H2O)6] 2+
[Fe(H2O)6] 3+
[Cu(H2O)6] 2+
[Al(H2O)6] 3+
What colour solution does Cu 2+ give when hydrated?
[Cu(H2O)6] 2+ (aq)
Blue solution
What colour solution does Fe 2+ give when hydrated?
[Fe(H2O)6] 2+ (aq)
Pale green solution
What colour solution does Fe 3+ give when hydrated?
[Fe(H2O)6] 3+ (aq)
Purple solution
may look yellow/brown
What colour solution does Al 3+ give when hydrated?
[Al(H2O)6] 3+ (aq)
Colourless solution
Why are the 3+ ions more acidic?
- Fe3+ smaller and more highly charged than Fe2+
- so Fe3+ more polarising
- Fe3+ attracts LP on oxygen of water ligands more strongly
- weakens O-H bond strength
- Fe3+ complex more easily releases H+
- Fe2+ does not release H+
What is the equation which represents [Fe(H2O)6] 3+ acting as an acid?
[Fe(H2O)6] 3+ —> [Fe(H2O)5(OH)] 2+ + H+
OR
[Fe(H2O)6] 3+ + H2O —> [Fe(H2O)5(OH)] 2+ + H3O+
What is the equation which represents [Al(H2O)6] 3+ acting as an acid?
[Al(H2O)6] 3+ —> [Al(H2O)5(OH)] 2+ + H+
OR
[Al(H2O)6] 3+ + H2O —> [Al(H2O)5(OH)] 2+ + H3O+
Reaction of [Fe(H2O)6] 2+ with Na2CO3
[Fe(H2O)6] 2+ + CO3 2- —> FeCO3 + 6H2O
green solution becomes green ppt FeCO3
Reaction of [Fe(H2O)6] 2+ with NaOH
[Fe(H2O)6] 2+ + 2OH- —> [Fe(H2O)4(OH)2] (s) + 2H2O
green solution becomes green ppt [Fe(H2O)4(OH)2] (s)
- green ppt goes brown on standing in air
- oxygen oxidises Fe2+ to Fe3+
Reaction of [Fe(H2O)6] 2+ with NH3
[Fe(H2O)6] 2+ + 2NH3 —> [Fe(H2O)4(OH)2] (s) + 2NH4+
- green solution becomes green ppt [Fe(H2O)4(OH)2] (s)
- green ppt goes brown on standing in air
- oxygen oxidises Fe2+ to Fe3+
Reaction of [Cu(H2O)6] 2+ with Na2CO3
[Cu(H2O)6] 2+ + CO3 2- —> CuCO3 (s) + 6H2O
- blue solution becomes blue/green ppt
Reaction of [Cu(H2O)6] 2+ with NaOH
[Cu(H2O)6] 2+ + 2OH- —> [Cu(H2O)4(OH)2] (s) + 2H2O
- blue solution becomes blue ppt [Cu(H2O)4(OH)2] (s)
Reaction of [Cu(H2O)6] 2+ with NH3
[Cu(H2O)6] 2+ + 2NH3 —> [Cu(H2O)4(OH)2] (s) + 2NH4+
- blue solution becomes blue ppt
Reaction of [Cu(H2O)6] 2+ in excess NH3
[Cu(H2O)6] 2+ + 4NH3 —> [Cu(H2O)2(NH3)4] 2+ (aq) + 4H2O
- blue solution becomes deep blue solution [Cu(H2O)2(NH3)4] 2+ (aq)
[Cu(H2O)6] 2+ + 4NH3 —> [Cu(H2O)2(NH3)4] 2+ (aq) + 2H2O + 2OH-
- blue solution becomes deep blue solution [Cu(H2O)2(NH3)4] (aq)
Reaction of [Cu(H2O)6] 2+ with HCl
[Cu(H2O)6] 2+ + 4Cl- —> [CuCl4] 2- (aq) + 6H2O
- blue solution —> yellow solution [CuCl4] 2- (aq)
- complex changes from octahedral to tetrahedral
Reaction of [Fe(H2O)6] 3+ with Na2CO3
2 [Fe(H2O)6] 3+ + 3CO3 2- —> 2[Fe(H2O)3(OH)3] (s) + 3CO2 + 3H2O
yellow/brown solution —> brown ppt and effervescence
- CO2 gas evolved
Reaction of [Fe(H2O)6] 3+ with NaOH
[Fe(H2O)6] 3+ + 3OH- —> Fe(H2O)3(OH)3] (s) + 3H2O
yellow/brown solution —> brown ppt
Reaction of [Fe(H2O)6] 3+ with NH3
[Fe(H2O)6] 3+ + 3NH3 —> [Fe(H2O)3(OH)3] + 3NH4+
yellow/brown solution —> brown ppt
Reaction of [Al(H2O)6] 3+ with Na2CO3
2 [Al(H2O)6] 3+ + 3CO3 2- —> 2[Al(H2O)3(OH)3] (s) + 3CO2 + 3H2O
colourless solution —> white ppt and effervescence
Reaction of [Al(H2O)6] 3+ with NaOH
[Al(H2O)6] 3+ + 3OH- —> [Al(H2O)3(OH)3] (s) + 3H2O
colourless solution —> white ppt [Al(H2O)3(OH)3] (s)
Reaction of [Al(H2O)6] 3+ with excess NaOH
[Al(H2O)6] 3+ + OH- —> [Al(H2O)2(OH)4] - (s) + H2O
white ppt dissolves to colourless solution
Reaction of [Al(H2O)6] 3+ with NH3
[Al(H2O)6] 3+ + 3NH3 —> [Al(H2O)3(OH)3] + 3NH4+
colourless solution —> white ppt
Show how aluminium hydroxide is amphoteric when HCl is added
[Al(H2O)3(OH)3] (s) + 3H+ —> [Al(H2O)6] 3+
acts as a base
Show how aluminium hydroxide is amphoteric when NaOH is added
[Al(H2O)3(OH)3] (s) + OH- —> [Al(H2O)2(OH)4] - (s) + H2O
acts as an acid
Explain, with the use of an equation, why a solution containing [Al(H2O)6]3+ has
a pH ˂7
[Al(H2O)6]3+ ⇌ [Al(H2O)5(OH)] 2+ + H+
- Al 3+ has small size and high charge
- weakens OH bond releasing H+ ions
Reaction of [Fe(H2O)6] 2+ with excess NH3
No further change
Reaction of [Fe(H2O)6] 3+ with excess NH3
No further change
Explain why an aqueous solution containing
[Fe(H2O)6]3+ ions has a lower pH than
an aqueous solution containing [Fe(H2O)6]2+ ions.
- Fe3+ is smaller (than Fe2+)
- Fe3+ ions are more polarising
- weaken O-H bonds in ligands more (in the Fe3+ solution) / more H+ released
Explain, with the use of an equation, why a solution containing [Al(H2O)6]3+ has
a pH ˂ 7
[Al(H2O)6]3+ ⇌ [Al(H2O)5(OH)]2+ + H+
M2 Al3+ has a small size and high charge
M3 Weakens the OH bond (in water) releasing H+ ions