Reactions of Aqueous Ions - Summary
1. Key Concepts & Glossary
Charge Density: Charge per unit volume of an ion; smaller, highly charged ions have higher charge
density.
Polarising Effect: A cation's ability to distort the electron cloud of nearby anions or ligands.
Precipitate: An insoluble solid formed in a reaction.
Hydrolysis: Reaction with water, often leading to H+ release.
Amphoteric: A substance that can act as both an acid and a base.
Ligand Substitution: Exchange of one ligand for another in a complex ion.
Chelating Ligand: A ligand forming multiple bonds with a metal ion.
Chelate Effect: Increased stability of complexes containing chelating ligands.
Entropy (Delta S): Measure of disorder; reactions tend to be feasible when entropy increases.
Feasible Reaction: One that can proceed under given conditions, often due to favorable entropy and
enthalpy changes.
2. Acidity of Hexaaqua Metal Ion Solutions
Hexaaqua ions: [M(H2O)6]3+ and [M(H2O)6]2+
Fe2+: [Fe(H2O)6]2+ - Weakly acidic
Fe3+: [Fe(H2O)6]3+ - Strongly acidic
Fe3+ is more acidic than Fe2+ because:
- Fe3+ has a higher charge density than Fe2+.
- It attracts electron density from O-H bonds in water ligands, making them weaker.
- This makes it easier to release H+, increasing acidity.
Reaction Example:
[Fe(H2O)6]3+ <-> [Fe(H2O)5(OH)]2+ + H+
3. Reactions with Sodium Hydroxide (NaOH)
Adding NaOH removes H+ from water ligands, forming an insoluble metal hydroxide.
General Equation:
[M(H2O)6]n+ + nOH- -> M(H2O)6-n(OH)n (s) + nH2O
Example Reactions:
1. Key Concepts & Glossary
Charge Density: Charge per unit volume of an ion; smaller, highly charged ions have higher charge
density.
Polarising Effect: A cation's ability to distort the electron cloud of nearby anions or ligands.
Precipitate: An insoluble solid formed in a reaction.
Hydrolysis: Reaction with water, often leading to H+ release.
Amphoteric: A substance that can act as both an acid and a base.
Ligand Substitution: Exchange of one ligand for another in a complex ion.
Chelating Ligand: A ligand forming multiple bonds with a metal ion.
Chelate Effect: Increased stability of complexes containing chelating ligands.
Entropy (Delta S): Measure of disorder; reactions tend to be feasible when entropy increases.
Feasible Reaction: One that can proceed under given conditions, often due to favorable entropy and
enthalpy changes.
2. Acidity of Hexaaqua Metal Ion Solutions
Hexaaqua ions: [M(H2O)6]3+ and [M(H2O)6]2+
Fe2+: [Fe(H2O)6]2+ - Weakly acidic
Fe3+: [Fe(H2O)6]3+ - Strongly acidic
Fe3+ is more acidic than Fe2+ because:
- Fe3+ has a higher charge density than Fe2+.
- It attracts electron density from O-H bonds in water ligands, making them weaker.
- This makes it easier to release H+, increasing acidity.
Reaction Example:
[Fe(H2O)6]3+ <-> [Fe(H2O)5(OH)]2+ + H+
3. Reactions with Sodium Hydroxide (NaOH)
Adding NaOH removes H+ from water ligands, forming an insoluble metal hydroxide.
General Equation:
[M(H2O)6]n+ + nOH- -> M(H2O)6-n(OH)n (s) + nH2O
Example Reactions:
