S = 0.05916 V (which is RT·ln10/F at 25 °C). Solids have activity = 1. Dissolved species activities come from the speciation solver. The effective pH-slope of each D-line kinks at every ligand pKa.
| Line | Half-reaction | E° (V) | Nernst expression |
|---|---|---|---|
| A0 | Ni²⁺ + 2e⁻ → Ni | −0.2405 | E = −0.2405 + (S/2)·log[Ni²⁺] |
| Ac1 | NiH₂cit⁺ + 2e⁻ → Ni + H₂cit⁻ | −0.2849 | E = −0.2849 + (S/2)·log([NiH₂cit⁺]/[H₂cit⁻]) |
| Ac2 | NiHCit + 2e⁻ → Ni + HCit²⁻ | −0.3458 | E = −0.3458 + (S/2)·log([NiHCit]/[HCit²⁻]) |
| Ac3 | NiCit⁻ + 2e⁻ → Ni + Cit³⁻ | −0.4019 | E = −0.4019 + (S/2)·log([NiCit⁻]/[Cit³⁻]) |
| Ac4 | NiCit₂⁴⁻ + 2e⁻ → Ni + 2Cit³⁻ | −0.4925 | E = −0.4925 + (S/2)·log([NiCit₂⁴⁻]/[Cit³⁻]²) |
| An1 | Ni(NH₃)²⁺ + 2e⁻ → Ni + NH₃ | −0.3236 | E = −0.3236 + (S/2)·(log[Ni(NH₃)²⁺] − log[NH₃]) |
| An2 | Ni(NH₃)₂²⁺ + 2e⁻ → Ni + 2NH₃ | −0.3908 | E = −0.3908 + (S/2)·(log[Ni(NH₃)₂²⁺] − 2·log[NH₃]) |
| An3 | Ni(NH₃)₃²⁺ + 2e⁻ → Ni + 3NH₃ | −0.4431 | E = −0.4431 + (S/2)·(log[Ni(NH₃)₃²⁺] − 3·log[NH₃]) |
| An4 | Ni(NH₃)₄²⁺ + 2e⁻ → Ni + 4NH₃ | −0.4807 | E = −0.4807 + (S/2)·(log[Ni(NH₃)₄²⁺] − 4·log[NH₃]) |
| An5 | Ni(NH₃)₅²⁺ + 2e⁻ → Ni + 5NH₃ | −0.5046 | E = −0.5046 + (S/2)·(log[Ni(NH₃)₅²⁺] − 5·log[NH₃]) |
| An6 | Ni(NH₃)₆²⁺ + 2e⁻ → Ni + 6NH₃ | −0.5090 | E = −0.5090 + (S/2)·(log[Ni(NH₃)₆²⁺] − 6·log[NH₃]) |
| B | Ni(OH)₂ + 2H⁺ + 2e⁻ → Ni + 2H₂O | +0.1098 | E = 0.1098 − S·pH |
| Line | Half-reaction | E° (V) | Nernst expression |
|---|---|---|---|
| D0 | Ni(OH)₃ + 3H⁺ + e⁻ → Ni²⁺ + 3H₂O | +2.2389 | E = 2.2389 − 3S·pH − S·log[Ni²⁺] |
| Dc1 | Ni(OH)₃ + 3H⁺ + H₂cit⁻ + e⁻ → NiH₂cit⁺ + 3H₂O | +2.1976 | E = 2.1976 − 3S·pH + S·log[H₂cit⁻] − S·log[NiH₂cit⁺] |
| Dc2 | Ni(OH)₃ + 3H⁺ + HCit²⁻ + e⁻ → NiHCit + 3H₂O | +2.4495 | E = 2.4495 − 3S·pH + S·log[HCit²⁻] − S·log[NiHCit] |
| Dc3 | Ni(OH)₃ + 3H⁺ + Cit³⁻ + e⁻ → NiCit⁻ + 3H₂O | +2.5619 | E = 2.5619 − 3S·pH + S·log[Cit³⁻] − S·log[NiCit⁻] |
| Dc4 | Ni(OH)₃ + 3H⁺ + 2Cit³⁻ + e⁻ → NiCit₂⁴⁻ + 3H₂O | +2.7429 | E = 2.7429 − 3S·pH + 2S·log[Cit³⁻] − S·log[NiCit₂⁴⁻] |
| Dn1 | Ni(OH)₃ + 3H⁺ + NH₃ + e⁻ → Ni(NH₃)²⁺ + 3H₂O | +2.4051 | E = 2.4051 − 3S·pH + S·log[NH₃] − S·log[Ni(NH₃)²⁺] |
| Dn2 | Ni(OH)₃ + 3H⁺ + 2NH₃ + e⁻ → Ni(NH₃)₂²⁺ + 3H₂O | +2.5394 | E = 2.5394 − 3S·pH + 2S·log[NH₃] − S·log[Ni(NH₃)₂²⁺] |
| Dn3 | Ni(OH)₃ + 3H⁺ + 3NH₃ + e⁻ → Ni(NH₃)₃²⁺ + 3H₂O | +2.6442 | E = 2.6442 − 3S·pH + 3S·log[NH₃] − S·log[Ni(NH₃)₃²⁺] |
| Dn4 | Ni(OH)₃ + 3H⁺ + 4NH₃ + e⁻ → Ni(NH₃)₄²⁺ + 3H₂O | +2.7194 | E = 2.7194 − 3S·pH + 4S·log[NH₃] − S·log[Ni(NH₃)₄²⁺] |
| Dn5 | Ni(OH)₃ + 3H⁺ + 5NH₃ + e⁻ → Ni(NH₃)₅²⁺ + 3H₂O | +2.7673 | E = 2.7673 − 3S·pH + 5S·log[NH₃] − S·log[Ni(NH₃)₅²⁺] |
| Dn6 | Ni(OH)₃ + 3H⁺ + 6NH₃ + e⁻ → Ni(NH₃)₆²⁺ + 3H₂O | +2.7762 | E = 2.7762 − 3S·pH + 6S·log[NH₃] − S·log[Ni(NH₃)₆²⁺] |
| C | Ni(OH)₃ + H⁺ + e⁻ → Ni(OH)₂ + H₂O | +1.308 | E = 1.308 − S·pH |
| Equilibrium | pKa |
|---|---|
| H₃cit ⇌ H₂cit⁻ + H⁺ | 2.95 |
| H₂cit⁻ ⇌ HCit²⁻ + H⁺ | 4.38 |
| HCit²⁻ ⇌ Cit³⁻ + H⁺ | 5.82 |
| NH₄⁺ ⇌ NH₃ + H⁺ | 9.25 |
| Equilibrium | log K or log β |
|---|---|
| Ni²⁺ + H₂cit⁻ ⇌ NiH₂cit⁺ | 1.5 |
| Ni²⁺ + HCit²⁻ ⇌ NiHCit | 3.56 |
| Ni²⁺ + Cit³⁻ ⇌ NiCit⁻ | 5.46 |
| Ni²⁺ + 2 Cit³⁻ ⇌ NiCit₂⁴⁻ (log β₂) | 8.52 |
| Ni²⁺ + n NH₃ ⇌ Ni(NH₃)ₙ²⁺ (log βₙ, n = 1…6) | 2.81 / 5.08 / 6.85 / 8.12 / 8.93 / 9.08 |
| Ni(OH)₂ ⇌ Ni²⁺ + 2 OH⁻ (Ksp) | −16.16 (Ksp = 6.96×10⁻¹⁷) |