Ions in aqueous solution

What are the four transition metal reaction types

• Redox- the oxidation number of the transition metal changes

• Deprotonation- one or more of the ligands loses or gains a hydrogen ion

• Ligand exchange- one or more of the ligands is replaced by a diff ligand

• Coordination number change- the total num of ligands in the complex changes

reactions of metal aqua ions with aqueous ammonia

• Solutions of metal aqua ions react as​ acids ​with aqueous ammonia

• This means that the ammonia solution will initially act as a​ base​ to remove one H⁺ ion per ammonia molecule used

  • Examples of ionic equations for this type of reaction from the table above:

    • [Fe(H₂O)₆]²⁺ (aq) + 2NH₃ (aq) → Fe(H₂O)₄(OH)₂ (s) + 2NH₄⁺ (aq)

  • This is deprotonation reaction- two hydroxide ions removing hydrogen ions from two of the water ligands convertign them into water moelcules

reaciton with limited OH- and NH3

• The bases OH^- and ammonia when in limited amounts form the same hydroxide precipitates.

• They form in deprotonation acid base reactions

• this is actually a deprotonation reaction - two hydroxide ions removing hydrogen ions from two of the water ligands converting them into water molecules

  • The two ligands that have lost hydrogen ions are now hydroxide ligand

reaction of metal aqua ions with excess ammonia

Some metal aqua ions will react further and undergo ligand substitution with excess ammonia

• Starting with the hexa aqua ions:

  • [Cu(H₂O)₆]²⁺ (aq) + 4NH₃ (aq) → [Cu(H₂O)₂(NH₃)₄]²⁺ (aq) + 4H₂O (l) 

  • [Co(H₂O)₆]²⁺ (aq) + 6NH₃ (aq) → [Co(NH₃)₆]²⁺ (aq) + 6H₂O (l) 

• Starting with the precipitates: 

  • [Cu(H₂O)₄(OH)₂] (s) + 4NH₃ (aq) → [Cu(H₂O)₂(NH₃)₄]²⁺ (aq) + 2H₂O (l) + 2OH^- (aq)

  • [Co(H₂O)₄(OH)₂] (s) + 6NH₃ (aq) → [Co(NH₃)₆]²⁺ (aq) + 4H₂O (l) + 2OH^- (aq)​

reaction with excess OH-

• When an excess of sodium hydroxide is added further deprotonation takes place

[Cr(H₂O)₃(OH)₃] (s) + 3OH^- (aq) → [Cr(OH)₆]^3- (aq) + 3H₂O (l) 

• In this reaction, chromium(III) hydroxide acts as an acid, as it is reacting with a base

• Chromium(III) hydroxide can also act as a base because it can react with acids as follows

[Cr(H₂O)₃(OH)₃] (s) + 3H⁺ (aq) → [Cr(H₂O)₆]³⁺ (aq) 

• A metal hydroxide that can act as both an acid and a base is called an amphoteric hydroxide

  • This is an example of amphoteric behaviour

Amphoteric definition

A substance that can act as both an acid and base

Amphoteric behaviour

The ability of a species to react with both acids and bases