Reactions of inorganic compounds in aqueous solutions - Chapter 24 Flashcards
Why are solutions of Fe3+ more acidic than solutions of Fe2+?
Fe3+ is both a smaller ion and more positively charged
Makes it more strongly polarising
So when forming an aqua ion the Fe3+ more strongly attracts the electrons from the oxygens on the water ligands
This weakens the O-H bond in the water ligands, and breaks some of them
This causes the H+ ion to be released, making the water more acidic
Because Fe2+ is less polarising fewer O-H bonds will break in solution
Fe3+ aqua ion reaction with water equation
Name the type of reaction
[Fe (H20)6] 3+ (aq) + H20 (l) ⇌ [Fe (H20)5 (OH)] 2+ (aq) + H30+ (aq)
Hydrolysis
M (H20)3 (OH)3 properties
Neutral (uncharged)
Insoluble (forms a precipitate)
M2+ aqa ion plus ammonia equation
[M (H20)6] 2+ (aq) + 2NH3 (aq) —-> M (H20)4 (OH)2] (s) + 2NH4+
Carbonates of transition metal ions rule
In general, carbonates of transition metal ions exist in oxidation states of 2+ but not in states of 3+.
What is the carbonate ion?
CO3 2-
Reaction of Fe3+ aqua ion with carbonate ions
2[Fe (H20)6] 3+ (aq) + 3CO3 2- (aq) —-> 2[Fe (H2O)3 (OH)3] (aq) + 3CO2 (g) + 3H20 (l)
What can you add to Fe3+ and Fe2+ aqua ions to better distinguish between them, and how does this work?
Add a dilute alkali (OH-)
The colours of the iron aqua ions are more difficult to tell apart when they are in their aqueous forms. Adding OH- causes them to form a coloured precipitate, and these have more distinct looking colours.
What can replace water as a ligand, and is replacement of water ligands complete or partial?
- Other neutral ligands, such as ammonia
- Negatively charged ligands, such as Cl- ions
- Replaced by multidentate ligands such as [EDTA] 4- (Chelation)
- Replacement of water ligands can be either complete or partial
When water is replaced by other neutral ligands, what change is seen in the co-ordination number?
None
Adding concentrated ammonia to [Co (H20)4 (OH)2] (s)
Write the equation and explain why this reaction occurs in the way it does
Give the colour changes
[Co (H20)4 (OH)2] (s) + 6NH3 (aq) ⇌ [Co (NH3)6] 2+ (aq) + 4H20 (l) + 2OH- (aq)
- Because ammonia is a better ligand than water
- The high ammonia concentration displaces equilibria, which displaces water and OH-
Blue precipitate to pale yellow solution
[X (H20)4 (OH)2] is called ion Y
When ion Y reacts with ammonia the water and hydroxide ion ligands are completely replaced by the ammonia
Give examples of what X could be
Magnesium
Cobalt
How many ethylene diamine ligands replace 6 water ligands? And what kind of ligand is ethylene diamine?
Three
Bidentate ligand
How many [EDTA]4- molecules replace six water ligands?
One
What is a chelate?
A complex with a polydentate ligand
Why are the formation of chelates favoured?
Because a large number of entities on the right side of the reaction means that there is a large entropy increase from the left side of the reaction to the right.
[Fe (H2O)6] 2+ colour and colours after adding bases
[Fe (H2O)6] 2+ = Pale green
OH- little Green gelatinous ppt of [Fe (H20)4 (OH)2]
OH- excess Green gelatinous ppt of [Fe (H20)4 (OH)2]
NH3 little Green gelatinous ppt of [Fe (H20)4 (OH)2]
NH3 excess Green gelatinous ppt of [Fe (H20)4 (OH)2]
CO3 2- Green ppt of FeCO3
[Cu (H2O)6] 2+ colour and colours after adding bases
[Cu (H2O)6] 2+ = Pale blue
OH- little Pale blue ppt of [Cu (H20)4 (OH)2]
OH- excess Pale blue ppt of [Cu (H20)4 (OH)2]
NH3 little Pale blue ppt of [Cu (H20)4 (OH)2]
NH3 excess Pale blue ppt of [Cu (NH3]4 (OH)2]
CO3 2- Blue-green ppt of CuCO3
[Fe (H2O)6] 3+ colour and colours after adding bases
[Fe (H2O)6] 3+ = yellow
OH- little Brown gelatinous ppt of [Fe (H20)3 (OH)3]
OH- excess Brown gelatinous ppt of [Fe (H20)3 (OH)3]
NH3 little Brown gelatinous ppt of [Fe (H20)3 (OH)3]
NH3 excess Brown gelatinous ppt of [Fe (H20)3 (OH)3]
CO3 2- Brown gelatinous ppt of [Fe (H20)3 (OH)3] and bubbles of CO2
[Al (H2O)6] 3+ colour and colours after adding bases
[Al (H2O)6] 3+ = Colourless
OH- little White ppt of [Al (H2O)3 (OH)3]
OH- excess Colourless solution of [Al (OH)4]-
NH3 little White ppt of [Al (H2O)3 (OH)3]
NHS excess White ppt of [Al (H2O)3 (OH)3]
CO3 2- White ppt of [Al (H2O)3 (OH)3] and bubbles of CO2
What shows the greater acidity of [M (H20)6] 3+ in comparison to [M (H20)6] 2+
When carbonate ions are added to M2+ ions, precipitates of the metal carbonate forms. When carbonate ions are added to M3+ ions, CO2 is produced instead.
