Reactions of Ions in Aqueous Solution

• In what form do most metal cations exist in aqueous solution?

  Hexa-aqua complex ion
• Main group metals form colored ions in aqueous solution.

  False
• Why are most transition metal ions colored in aqueous solution?

  Incomplete d-sub shell
• Transition metal ions absorb specific wavelengths of visible light
• Match the metal ion formula with its color:

  [Fe(H₂O)6]²+ ↔️ Green

  [Cu(H₂O)6]²+ ↔️ Blue

  [Fe(H₂O)6]³+ ↔️ (Purple) or Yellow-brown

  [Al(H₂O)6]³+ ↔️ Colourless
• A Bronsted-Lowry acid is a substance that donates H+ ions.
• Hydrolysis involves the breaking of a bond using water
• What happens if a metal ion has sufficient polarising power on water ligands?

  Proton is donated
• The hydrolysis reaction of [Fe(H₂O)6]²+ with water produces [Fe(H₂O)5(OH)]⁺ and H₃O⁺
• Order the following compounds from most acidic to least acidic based on their pK₁ values: [Fe(H₂O)6]³+, [Fe(H₂O)6]²+, [Cu(H₂O)6]²+, [Al(H₂O)6]³+

  1️⃣ [Fe(H₂O)6]³+ (pK₁ = 2.46)

  2️⃣ [Al(H₂O)6]³+ (pK₁ = 4.85)

  3️⃣ [Fe(H₂O)6]²+ (pK₁ = 5.89)

  4️⃣ [Cu(H₂O)6]²+ (pK₁ = 7.49)
• A lower pK₁ value indicates a stronger acid.
• What is the primary reason for the difference in acidity between Fe³⁺ and Fe²⁺ aqua ions?

  Charge/size ratio
• The reaction of [Al(H₂O)6]³⁺ with water produces [Al(H₂O)5(OH)]²⁺ and H₃O⁺
• Which aqua-ion has the lowest pH and why?

  [Al(H₂O)6]³⁺, smaller charge/size ratio
• Adding a base to a solution of a metal-aqua ion produces an insoluble metal hydroxide precipitate.
• What precipitate is formed when sodium hydroxide reacts with [Fe(H₂O)6]³⁺?

  [Fe(H₂O)3(OH)3]
• An amphoteric species can act as both an acid and a base.
• [Al(H₂O)3(OH)3] reacts with excess OH⁻ to form [Al(H₂O)₂(OH)₄]⁻ and H₂O
• What precipitate is formed when sodium hydroxide reacts with [Cu(H₂O)6]²⁺?

  [Cu(H₂O)4(OH)₂]
• Aqueous ammonia is a weak base.
• What is the reaction of [Fe(H₂O)6]³⁺ with aqueous ammonia?

  [Fe(H₂O)6]³⁺ + 3NH₃ → [Fe(H₂O)3(OH)3] + 3NH₄⁺
• The solution of [Fe(H₂O)6]²+ is green
• When sodium hydroxide is added to [Fe(H₂O)6]²+, a green precipitate
• The green precipitate of [Fe(H₂O)4(OH)₂] turns brown in air due to oxidation to iron(III) hydroxide.
• The solution of [Cu(H₂O)6]²+ is blue
• When sodium hydroxide is added to [Cu(H₂O)6]²+, a pale blue precipitate
• Ammonia is a weak base and reacts with metal-aqua ions to produce metal hydroxides.
• When [Fe(H₂O)6]³+ reacts with ammonia, a brown precipitate
• When [Al(H₂O)6]³+ reacts with ammonia, a white precipitate
• Ammonia cannot hydrolyse [Al(H₂O)3(OH)3] further.
• When [Cu(H₂O)6]²+ reacts with ammonia, a pale blue precipitate
• When excess ammonia is added to [Cu(H₂O)4(OH)₂], a new complex called [Cu(H₂O)₂(NH3)4]²+ is formed, which is deep blue.
• The 2+ metal ions react with sodium carbonate to form insoluble metal carbonates.
• When [Fe(H₂O)6]²+ reacts with sodium carbonate, a green precipitate
• When [Fe(H₂O)6]³+ reacts with sodium carbonate, carbon dioxide gas is released
• Metal hydroxides of Al³+ exhibit amphoteric character
• Match the reaction with the correct precipitate formed:

  [Fe(H₂O)6]²+ + OH¯ ↔️ [Fe(H₂O)4(OH)₂]

  [Cu(H₂O)6]²+ + NH3 ↔️ [Cu(H₂O)4(OH)₂]

  [Al(H₂O)6]³+ + CO3²¯ ↔️ [Al(H₂O)3(OH)3]