Question

Name each of the following complex ions and identify the oxidation number of the metal: (a) [Fe(CN)6]42; (b) [Co(NH3)6]31; (c) [Co(CN)5(OH2)]22; (d) [Co(NH3)5(SO4)]1.

Answer 1

Answer:

(a) [Fe(CN)₆]⁴⁻ - Hexacyanoferrate(II) ion

Central metal atom -  Fe

Oxidation state of central metal Fe = +2

(b) [Co(NH₃)₆]³⁺ : Hexamminecobalt(III) ion

Central metal atom -  Co

Oxidation state of central metal Co = +3

(c) [Co(CN)₅(OH₂)]²⁻ : Aquapentacyanidocobalt(III) ion

Central metal atom -  Co

Oxidation state of central metal Co = +3

(d) [Co(NH₃)₅(SO₄)]⁺ :  Pentaamminesulfatocobalt(III) ion

Central metal atom -  Co

Oxidation state of central metal Co = +3

Explanation:

Oxidation number, also known as oxidation state, describes the number of electrons lost or gained by a chemical element.

(a) [Fe(CN)₆]⁴⁻ - Hexacyanoferrate(II) ion

Central metal atom -  Fe

Let the oxidation state of Fe = x

Charge on CN⁻ ligand = (-1)

x + (-1) × 6 = -4

⇒ x = -4 + 6 = +2

Oxidation state of Fe: x = +2

(b) [Co(NH₃)₆]³⁺ : Hexamminecobalt(III) ion

Central metal atom -  Co

Let the oxidation state of Co = x

Charge on NH₃ ligand = 0

x + (0) × 6 = +3

⇒ x = +3

Oxidation state of Co: x = +3

(c) [Co(CN)₅(OH₂)]²⁻ : Aquapentacyanidocobalt(III) ion

Central metal atom -  Co

Let the oxidation state of Co = x

Charge on CN⁻ ligand = -1

Charge on H₂O ligand = 0

x + (-1) × 5 + 0 × 1 = -2

⇒ x = +3

Oxidation state of Co: x = +3

(d) [Co(NH₃)₅(SO₄)]⁺ :  Pentaamminesulfatocobalt(III) ion

Central metal atom -  Co

Let the oxidation state of Co = x

Charge on NH₃ ligand = 0

Charge on SO₄²⁻ ligand = -2

x + (0) × 5 + (-2) × 1 = +1

⇒ x = +3

Oxidation state of Co: x = +3