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P4: Polarographic Half-Wave Potentials

The following table provides E1/2 values for selected reduction reactions. Values are from Dean, J. A. Analytical Chemistry Handbook, McGraw-Hill: New York, 1995.

Element E1/2 (volts vs. SCE) Matrix
Al3+ + 3e ⇋ Al(s) –0.5 0.2 M acetate (pH 4.5–4.7)
Cd2+ + 2e ⇋ Cd(s) –0.60 0.1 M KCl
0.05 M H2SO4
1 M HNO3
Cr3+ + 3e ⇋ Cr(s) –0.35 (+3 → +2)
–1.70 (+2 → 0)
1 M NH4Cl plus 1 M NH3
1 M NH4+/NH3 buffer (ph 8–9)
Co3+ + 3e ⇋ Co(s) –0.5 (+3 → +2)
–1.3 (+2 → 0)
1 M NH4Cl plus 1 M NH3
Co2+ + 2e ⇋ Co(s) –1.03 1 M KSCN

Cu2+ + 2e ⇋ Cu(s)

0.04


–0.22
0.1 M KSCN
0.1 M NH4ClO4
1 M Na2SO4
0.5 M potassium citrate (pH 7.5)
Fe3+ + 3e ⇋ Fe(s) –0.17 (+3 → +2)
–1.52 (+2 → 0)
0.5 M sodium tartrate (pH 5.8)

Fe3+ + e ⇋ Fe2+

–0.27 0.2 M Na2C2O4 (pH < 7.9)
Pb2+ + 2e ⇋ Pb(s) –0.405
–0.435
1 M HNO3
1 M KCl
Mn2+ + 2e ⇋ Mn(s) –1.65 1 M NH4Cl plus 1 M NH3
Ni2+ + 2e ⇋ Ni(s)

–0.70
–1.09

1 M KSCN
1 M NH4Cl plus 1 M NH3

Zn2+ + 2e ⇋ Zn(s)

–0.995
–1.33
0.1 M KCl
1 M NH4Cl plus 1 M NH3