Ligand Substitution Reactions

Question 1

Cu²⁺ in aqueous ammonia

EQUATIONS AND OBSERVATIONS

Answer 1

• [Cu(H₂O)₆]²⁺(aq) + 2NH₃(aq) -> [Cu(OH)₂(H₂O)₄] + 2NH₄⁺
• [Cu(OH)₂(H₂O)₄] dissolves in excess ammonia to form [Cu(NH₃)₄(H₂O)₂]²⁺(aq)

Blue solution reacts to form a blue precipitate. The precipitate is soluble in excess ammonia which then forms a deep blue solution

Question 2

Cr³⁺ in aqueous ammonia

EQUATIONS AND OBSERVATIONS

Answer 2

• [Cr(H₂O)₆]³⁺(aq) + 3NH₃(aq) -> [Cr(OH)₃(H₂O)₃] + 3NH₄⁺
• [Cr(OH)₃(H₂O)₃] dissolves in excess ammonia to form [Cr(NH₃)₆]³⁺(aq)

A violet solution reacts to form a grey-green precipitate, the precipitate is then soluble in excess ammonia, forming a purple solution

Question 3

Fe²⁺ with aqueous ammonia

EQUATIONS AND OBSERVATIONS

Answer 3

• [Fe(H₂O)₆]²⁺(aq) + 2NH₃(aq) -> [Fe(OH)₂(H₂O)₄] + 2NH₄⁺(aq)
• NO further reaction with excess ammonia

A pale green solution reacts to form a green precipitate. The precipitate is insoluble in excess ammonia but turns brown on its surface due to being oxidised to Fe(III) by the air

Question 4

Fe³⁺ with aqueous ammonia

EQUATIONS AND OBSERVATIONS

Answer 4

• [Fe(H₂O)₆]³⁺(aq) + 3NH₃(aq) -> [Fe(OH)₃(H₂O)₃] + 3NH₄⁺(aq)
• NO further reaction with excess ammonia

Pale yellow solution reacts to form an orange brown precipitate. The precipitate is insoluble in excess ammonia

Question 5

Mn²⁺ with aqueous ammonia

EQUATIONS AND OBSERVATIONS

Answer 5

• [Mn(H₂O)₆]²⁺(aq) + 2NH₃(aq) -> [Mn(OH)₂(H₂O)₄] + 2NH₄⁺(aq)
• NO further reaction with excess ammonia

Pale pink solution reacts to form a light brown precipitate which darkens on standing in air. Insoluble in excess ammonia

Question 6

Cu²⁺ with Chloride ions:

EQUATIONS AND OBSERVATIONS

Answer 6

• [Cu(H₂O)₆]²⁺(aq) + 4Cl⁻(aq) ⇌ [CuCl₄]²⁻(aq) + 6H₂O(l)

Apale blue solution will form a yellow solution

Question 7

Cr³⁺ with aqueous NaOH

EQUATIONS AND OBSERVATIONS

Answer 7

• [Cr(H₂O)₆]³⁺(aq) + 3OH⁻(aq) -> [Cr(OH)₃(H₂O)₃] + 3H₂O
• [Cr(OH)₃(H₂O)₃] reacts with excess NaOH in the reaction:
  [Cr(OH)₃(H₂O)₃] + 3OH⁻(aq) -> [Cr(OH)₆]³⁻(aq)

A violet solution reacts to form a grey-green precipitate, the precipitate is soluble in excess sodium hydroxide forming a dark green solution

Question 8

Cu²⁺ with aqueous NaOH

EQUATIONS AND OBSERVATIONS

Answer 8

• [Cu(H₂O)₆]²⁺(aq) + 2OH⁻(aq) -> [Cu(OH)₂(H₂O)₄] + 2H₂O

Blue solution reacts to form a blue precipitate. The precipitate is insoluble in excess sodium hydroxide

Question 9

Fe²⁺ in aqueous NaOH

EQUATIONS AND OBSERVATIONS

Answer 9

• [Fe(H₂O)₆]²⁺(aq) + 2OH⁻(aq) -> [Fe(OH)₂(H₂O)₄] + 2H₂O(aq)

A pale green solution reacts to form a green precipitate. The precipitate is insoluble in excess NaOH but turns brown on its surface due to being oxidised to Fe(III) by the air

Question 10

Fe³⁺ in NaOH

EQUATIONS AND OBSERVATIONS

Answer 10

• [Fe(H₂O)₆]³⁺(aq) + 3OH⁻(aq) -> [Fe(OH)₃(H₂O)₃] + 3H₂O(aq)

Pale yellow solution reacts to form an orange brown precipitate. The precipitate is insoluble in excess NaOH

Question 11

Mn²⁺ in aqueous NaOH

EQUATIONS AND OBSERVATIONS

Answer 11

• [Mn(H₂O)₆]²⁺(aq) + 2OH⁻(aq) -> [Mn(OH)₂(H₂O)₄] + 2H₂O(aq)

Pale pink solution reacts to form a light brown precipitate which darkens on standing in air. Insoluble in excess NaOH