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STANDARD ELECTRODE POTENTIALS |
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See Chemical Ideas 9.2 Redox reactions and electrode
potentials for details The value of E indicates the willingness of a
half-cell to be reduced (i.e. it is a reduction potential). It shows the how many volts are required to make
the system undergo the specified reduction, compared to a standard hydrogen
half-cell, whose standard electrode potential is defined as 0.00 V. At the top of the list is the most powerful
reducing agent – the species that is least easily reduced. Standard conditions are 298 K temperature, 1 atm pressure and 1.0 mol dm-3 concentrations. Ecell = E(right-hand
electrode) – E(left-hand electrode) (all
under standard conditions) |
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|
HALF CELL |
NOTES |
REDUCTION HALF-EQUATION |
E / Volts (standard conditions) |
|
Lithium |
|
Li+(aq) + e-
→ Li(s) |
-3.04 |
|
Potassium |
|
K+(aq) + e-
→K(s) |
-2.92 |
|
Barium |
|
Ba2+ (aq) + 2e-
→Ba(s) |
-2.90 |
|
Calcium |
|
Ca2+ (aq) + 2e-
→Ca(s) |
-2.84 |
|
Sodium |
|
Na+(aq) + e-
→ Na(s) |
-2.71 |
|
Magnesium |
|
Mg2+(aq) + 2e-
→ Mg(s) |
-2.37 |
|
Aluminium |
|
Al3+(aq) + 3e-
→ Al(s) |
-1.68 |
|
Manganese(II) |
|
Mn2+ (aq) + 2e-
→Mn(s) |
-1.18 |
|
Zinc |
|
Zn2+(aq) + 2e-
→ Zn(s) |
-0.76 |
|
Chromium(III) |
|
Cr3+ (aq) + 3e-
→Cr(s) |
-0.74 |
|
Iron(II) |
|
Fe2+(aq) + 2e-
→ Fe(s) |
-0.44 |
|
Chromium(III)-(II) |
|
Cr3+ (aq) + e-
→ Cr2+ (aq) |
-0.41 |
|
Cadmium |
|
Cd2+(aq) + 2e-
→ Cd(s) |
-0.40 |
|
Cobalt(II) |
|
Co2+(aq) + 2e-
→ Co(s) |
-0.28 |
|
Nickel(II) |
|
Ni2+(aq) + 2e-
→ Ni(s) |
-0.26 |
|
Tin(II) |
|
Sn2+(aq) + 2e-
→ Sn(s) |
-0.14 |
|
Lead(II) |
|
Pb2+(aq) + 2e-
→ Pb(s) |
-0.13 |
|
Hydrogen |
Special
conditions. See Chemical Ideas page
213 figure 11. |
2H+(aq) + 2e-
→ H2(g) |
+0.00 |
|
Tin(IV) |
|
Sn4+(aq) + 2e-
→ Sn2+(aq) |
+0.15 |
|
Copper(II)-(I) |
|
Cu2+(aq) + e-
→ Cu+(aq) |
+0.15 |
|
Copper(II) |
|
Cu2+(aq) + 2e-
→ Cu(s) |
+0.34 |
|
Oxygen-water |
|
O2(g) + 2H2O
(l) + 4e- →
4OH-(aq) |
+0.40 |
|
Copper(I) |
|
Cu+(aq) + e-
→ Cu(s) |
+0.52 |
|
Iodine |
Inert platinum
electrode, aqueous solution of iodide ions and iodine molecules. |
I2(aq) + 2e-
→ 2I-(aq) |
+0.54 |
|
Manganese(VII)-(IV) |
|
Mn7+(aq) + 3e-
→ Mn4+(aq) |
+0.58 |
|
Iron(III)-(II) |
|
Fe3+(aq) + e-
→ Fe2+(aq) |
+0.77 |
|
Mercury(I) |
|
Hg22+
+ 2e- → 2Hg(s) |
+0.79 |
|
Silver |
|
Ag+(aq) + e-
→ Ag(s) |
+0.80 |
|
Bromine |
Inert platinum
electrode, aqueous solution of bromide ions and bromine molecules. |
Br2(aq) + 2e-
→ 2Br-(aq) |
+1.07 |
|
Manganese(IV)-(II) |
|
Mn4+(aq) + 2e-
→ Mn2+(aq) |
+1.21 |
|
Oxygen-acid |
Oxygen
gas dissolved in an acidic aqueous solution |
O2(g) + 4H+(aq)
+ 4e- →
2H2O(l) |
+1.23 |
|
Hydrogen peroxide |
|
H2O2(aq)
+ 2H+(aq) + 2e- → 2H2O(l) |
+1.23? |
|
Dichromate(VII) |
Acidified
dichromate(VII) solution |
Cr2O72-(aq)
+ 14H+(aq) + 6e- → 2Cr3+(aq)
+ 7H2O(l) |
+1.36 |
|
Chlorine |
Inert
platinum electrode, aqueous solution of chloride ions and chlorine molecules. |
Cl2(aq) + 2e-
→ 2Cl-(aq) |
+1.36 |
|
Gold(III) |
|
Au3+(aq) + 3e-
→ Au(s) |
+1.50 |
|
Manganate(VII) |
Acidified
manganate(VII) solution |
MnO4-(aq)
+ 8H+(aq) + 5e- → Mn2+(aq)
+ 4H2O(l) |
+1.51 |
|
Cobalt(III)-(II) |
|
Co+3(aq) + e-
→ Co2+(aq) |
+1.82 |
|
Fluorine |
|
F2(aq) + 2e-
→ 2F-(aq) |
+2.87 |