Reactions of Inorganic Compounds in Aqueous Solution Flashcards
Explain why aqueous solution for M3+ is more acidic than M2+
- higher charge density
- more strongly polarising so attracts electrons from oxygen on water ligand
- weakens OH bonds
- increases tendency of complex ion to release H+
Give an equation to show hydrolysis of [Fe(H2O)6]3+
[Fe(H2O)6]3+ -> [Fe(H2O)5OH]2+ + H+ OR
[Fe(H2O)6]3+ + H2O -> [Fe(H2O)5OH]2+ + H3O+
Lewis Acid
electron pair acceptor
Lewis Base
electron pair donor
Colour of [Fe(H2O)6]2+
pale green solution
Colour of [Fe(H2O)6]3+
pale purple solution
Explain why [Fe(H2O)6]3+ can appear yellow/brown
- hydrolysis of [Fe(H2O)6]3+
- presence of [Fe(H2O)5OH]2+
Describe how to distinguish between Fe2+ (aq) and Fe3+ (aq) since they are both pale in colour
- addition of base (NaOH)
- form coloured precipitates which are easily distinguishable
Give equation to show addition of base to M2+ (aq) to form metal hydroxide precipitate
[M(H2O)6]2+ + 2OH- -> [M(H2O)4(OH)2] + 2H2O
Give equation to show addition of base to M3+ (aq) to form metal hydroxide precipitate
[M(H2O)6]3+ + 3OH- -> [M(H2O)3(OH)3] + 3H2O
Give colour of [Fe(H2O)4(OH)2] and explain why it turns brown on standing
- green ppt
- some Fe2+ (aq) oxidises to Fe3+ (aq) which forms brown ppt of [Fe(H2O)3(OH)3]
Give equation to show acid-base reaction between M2+ (aq) and NH3 at low concentrations
[M(H2O)6]2+ + 2NH3 -> [M(H2O)4(OH)2] + 2NH4+
Give equation to show acid-base reaction between M3+ (aq) and NH3 at low concentrations
[M(H2O)6]3+ + 3NH3 -> [M(H2O)3(OH)3] + 3NH4+
Explain how acid-base reactions with CO32- can demonstrate relative acidity of M2+ (aq) and M3+ (aq)
- M2+ produces metal carbonate only
- M3+ is acidic enough to produce CO2 gas from CO32-
Explain why carbonates of transition metals have an oxidation state of +2 but not +3
- metal with oxidation state of +3 is acidic enough to liberate CO2 from CO32- so will not form carbonate with M3+
- M2+ will form metal carbonate since it is less acidic
Give the intermediate stage and overall equation for reaction between M3+ (aq) and CO32-
[M(H2O)6]3+ + 3CO32- -> [M(H2O)3(OH)3] + 3HCO3-
2[M(H2O)6]3+ + 3CO32- -> 2[M(H2O)3(OH)3] + 3CO2 + 3H2O
Give equation to show reaction between M2+ (aq) and CO32-
[M(H2O)6]2+ + CO32- -> MCO3 + 6H2O
Colour of FeCO3 precipitate
green ppt
Colour of [Al(H2O)6]3+
colourless solution
Give equation to show addition of base to Al3+ (aq) and observations
[Al(H2O)6]3+ + 3OH- -> [Al(H2O)3(OH)3] + 3H2O
white ppt of aluminium oxide formed
Give equations to show how [Al(H2O)3(OH)3] behaves as an amphoteric hydroxide
[Al(H2O)3(OH)3] + 3H+ -> [Al(H2O)6]3+
[Al(H2O)3(OH)3] + OH- -> [Al(OH)4]- + 3H2O
Give equation to show reaction between Al3+ (aq) and NH3 in low concentrations
[Al(H2O)6]3+ + 3NH3 -> [Al(H2O)3(OH)3] + 3NH4+
Explain why addition of base to Al3+ (aq) results in formation of white aluminium hydroxide precipitate but colourless solution in excess
- formation of [Al(H2O)3(OH)3] to begin with which is white precipitate
- [Al(H2O)3(OH)3] reacts with base to form [Al(OH)4]- which is colourless solution
Explain why ligand substitution of H2O with NH3 occurs in transition metal complexes and why it occurs without a change in charge or oxidation number
- NH3 is stronger ligand than H2O
- N is more electronegative than O so more likely to donate electron pair to central metal ion
- NH3 is same size and charge to H2O