35.8: Standard Reduction Potentials & Polarographic Half-wave Potentials
- Page ID
- 362971
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Standard/Formal Reduction Potentials
The following table provides Eo and Eo ́ values for selected reduction reactions. Values are from the following sources (primarily the first two):
- Bard, A. J.; Parsons, B.; Jordon, J., eds. Standard Potentials in Aqueous Solutions, Dekker: New York, 1985
- Milazzo, G.; Caroli, S.; Sharma, V. K. Tables of Standard Electrode Potentials, Wiley: London, 1978;
- Swift, E. H.; Butler, E. A. Quantitative Measurements and Chemical Equilibria, Freeman: New York, 1972.
- Bratsch, S. G. "Standard Electrode Potentials and Temperature Coefficients in Water at 298.15K, J. Phys. Chem. Ref. Data, 1989, 18, 1–21.
- Latimer, W. M. Oxidation Potentials, 2nd. Ed., Prentice-Hall: Englewood Cliffs, NJ, 1952
Solids, gases, and liquids are identified; all other species are aqueous. Reduction reactions in acidic solution are written using H+ in place of H3O+. You may rewrite a reaction by replacing H+ with H3O+ and adding to the opposite side of the reaction one molecule of H2O per H+; thus
H3AsO4 + 2H+ +2e– \(\rightleftharpoons\) HAsO2 +2H2O
becomes
H3AsO4 + 2H3O+ +2e– \(\rightleftharpoons\) HAsO2 +4H2O
Conditions for formal potentials (Eo ́) are listed next to the potential.
For most of the reduction half-reactions gathered here, there are minor differences in values provided by the references above. In most cases, these differences are small and will not affect calculations. In a few cases the differences are not insignificant and the user may find discrepancies in calculations. For example, Bard, Parsons, and Jordon report an Eo value of –1.285 V for
\[\text{Zn(OH)}_4^{2-} + 2e^- \rightleftharpoons \text{Zn}(s) + 4\text{OH}^-\nonumber \]
while Milazzo, Caroli, and Sharma report the value as –1.214 V, Swift reports the value as –1.22, Bratsch reports the value as –1.199 V, and Latimer reports the value as –1.216 V.
| Aluminum | E (V) | Eo ́ (V) |
|---|---|---|
| \(\text{Al}^{3+} + 3e^- \rightleftharpoons \text{Al}(s)\) | –1.676 | |
| \(\text{Al(OH)}_4^- + 3e^- \rightleftharpoons \text{Al}(s) + 4\text{OH}^-\) | –2.310 | |
| \(\text{AlF}_6^{3-} + 3e^- \rightleftharpoons \text{Al}(s) + 6\text{F}^-\) | –2.07 |
| Antimony | E (V) | Eo ́ (V) |
|---|---|---|
| \(\text{Sb} + 3\text{H}^+ + 3e^- \rightleftharpoons \text{SbH}_3(g)\) | –0.510 | |
| \(\text{Sb}_2\text{O}_5 + 6\text{H}^+ + 4e^- \rightleftharpoons 2\text{SbO}^+ + 3\text{H}_2\text{O}(l)\) | 0.605 | |
| \(\text{SbO}^+ + 2\text{H}^+ + 3e^- \rightleftharpoons \text{Sb}(s) + \text{H}_2\text{O}(l)\) | 0.212 |
| Arsenic | E (V) | Eo ́ (V) |
|---|---|---|
| \(\text{As}(s) + 3\text{H}^+ + 3e^- \rightleftharpoons \text{AsH}_3(g)\) | –0.225 | |
| \(\text{H}_3\text{AsO}_4 + 2\text{H}^+ + 2e^- \rightleftharpoons \text{HAsO}_2 + 2\text{H}_2\text{O}(l)\) | 0.560 | |
| \(\text{HAsO}_2 + 3\text{H}^+ + 3e^- \rightleftharpoons \text{As}(s) + 2\text{H}_2\text{O}(l)\) | 0.240 |
| Barium | E (V) | Eo ́ (V) |
|---|---|---|
| \(\text{Ba}^{2+} + 2e^- \rightleftharpoons \text{Ba}(s)\) | –2.92 | |
| \(\text{BaO}(s) + 2\text{H}^+ + 2e^- \rightleftharpoons \text{Ba}(s) + \text{H}_2\text{O}(l)\) | –2.166 |
| Beryllium | E (V) | Eo ́ (V) |
|---|---|---|
| \(\text{Be}^{2+} + 2e^- \rightleftharpoons \text{Be}(s)\) | –1.99 |
| Bismuth | E (V) | Eo ́ (V) |
|---|---|---|
| \(\text{Bi}^{3+} + 3e^- \rightleftharpoons \text{Bi}(s)\) | 0.317 | |
| \(\text{BiCl}_4^- + 3e^- \rightleftharpoons \text{Bi}(s) + 4\text{Cl}^-\) | 0.199 |
| Boron | E (V) | Eo ́ (V) |
|---|---|---|
| \(\text{B(OH)}_3 + 3\text{H}^+ + 3e^- \rightleftharpoons \text{B}(s) + 3\text{H}_2\text{O}(l)\) | –0.890 | |
| \(\text{B(OH)}_4^- + 3e^- \rightleftharpoons \text{B}(s) + 4\text{OH}^-\) | –1.811 |
| Bromine | E (V) | Eo ́ (V) |
|---|---|---|
| \(\text{Br}_2(l) + 2e^- \rightleftharpoons 2\text{Br}^-\) | 1.087 | |
| \(\text{HOBr} + \text{H}^+ + 2e^- \rightleftharpoons \text{Br}^- + \text{H}_2\text{O}(l)\) | 1.341 | |
| \(\text{HOBr} + \text{H}^+ + e^- \rightleftharpoons \frac{1}{2} \text{Br}_2 + \text{H}_2\text{O}(l)\) | 1.604 | |
| \(\text{BrO}^- + \text{H}_2\text{O}(l) + 2e^- \rightleftharpoons \text{Br}^- + 2\text{OH}^-\) | 0.76 in 1 M NaOH | |
| \(\text{BrO}_3^- +6\text{H}^+ + 5e^- \rightleftharpoons \frac{1}{2} \text{Br}_2(l) + 3\text{H}_2\text{O}(l)\) | 1.5 | |
| \(\text{BrO}_3^- + 6\text{H}^+ +6e^- \rightleftharpoons \text{Br}^- + 3\text{H}_2\text{O}(l)\) | 1.478 |
| Cadmium | E (V) | Eo ́ (V) |
|---|---|---|
| \(\text{Cd}^{2+} + 2e^- \rightleftharpoons \text{Cd}(s)\) | –0.4030 | |
| \(\text{Cd(CN)}_4^{2-} + 2e^- \rightleftharpoons \text{Cd}(s) + 4\text{CN}^-\) | –0.943 | |
| \(\text{Cd(NH}_3)_4^{2+} + 2e^- \rightleftharpoons \text{Cd}(s) + 4\text{NH}_3\) | –0.622 |
| Calcium | E (V) | Eo ́ (V) |
|---|---|---|
| \(\text{Ca}^{2+} + 2e^- \rightleftharpoons \text{Ca}(s)\) | –2.84 |
| Carbon | E (V) | Eo ́ (V) |
|---|---|---|
| \(\text{CO}_2(g) + 2\text{H}^+ + 2e^- \rightleftharpoons \text{CO}(g) + \text{H}_2\text{O}(l)\) | –0.106 | |
| \(\text{CO}_2(g) + 2\text{H}^+ +2e^- \rightleftharpoons \text{HCO}_2\text{H}\) | –0.20 | |
| \(2\text{CO}_2(g) + 2\text{H}^+ +2e^- \rightleftharpoons \text{H}_2\text{C}_2\text{O}_4\) | –0.481 | |
| \(\text{HCHO} + 2\text{H}^+ + 2e^- \rightleftharpoons \text{CH}_3\text{OH}\) | 0.2323 |
| Cerium | E (V) | Eo ́ (V) |
|---|---|---|
| \(\text{Ce}^{3+} + 3e^- \rightleftharpoons \text{Ce}(s)\) | –2.336 | |
| \(\text{Ce}^{4+} + e^- \rightleftharpoons \text{Ce}^{3+}\) | 1.72 |
1.70 in 1 M HClO4 1.44 in 1 M H2SO4 1.61 in 1 M HNO3 1.28 in 1 M HCl |
| Chlorine | E (V) | Eo ́ (V) |
|---|---|---|
| \(\text{Cl}_2(g) + 2e^- \rightleftharpoons 2\text{Cl}^-\) | 1.396 | |
| \(\text{ClO}^- + \text{H}_2\text{O}(l) + e^- \rightleftharpoons \frac{1}{2} \text{Cl}_2(g) + 2\text{OH}^-\) | 0.421 in 1 M NaOH | |
| \(\text{ClO}^- + \text{H}_2\text{O}(l) + 2e^- \rightleftharpoons \text{Cl}^- + 2\text{OH}^-\) | 0.890 in 1 M NaOH | |
| \(\text{HClO}_2 + 2\text{H}^+ + 2e^- \rightleftharpoons \text{HOCl} + \text{H}_2\text{O}(l)\) | 1.64 |
| Chlorine | E (V) | Eo ́ (V) |
|---|---|---|
| \(\text{ClO}_3^- + 2\text{H}^+ + e^- \rightleftharpoons \text{ClO}_2(g) + \text{H}_2\text{O}(l)\) | 1.175 | |
| \(\text{ClO}_3^- + 3\text{H}^+ + 2e^- \rightleftharpoons \text{HClO}_2 + \text{H}_2\text{O}(l)\) | 1.181 | |
| \(\text{ClO}_4^- + 2\text{H}^+ +2e^- \rightleftharpoons \text{ClO}_3^- + \text{H}_2\text{O}(l)\) | 1.201 |
| Chromium | E (V) | Eo ́ (V) |
|---|---|---|
| \(\text{Cr}^{3+} + 3e^- \rightleftharpoons \text{Cr}(s)\) | –0.424 | |
| \(\text{Cr}^{2+} + 2e^- \rightleftharpoons \text{Cr}(s)\) | –0.90 | |
| \(\text{Cr}_2\text{O}_7^{2-} + 14\text{H}^+ + 6e^- \rightleftharpoons 2\text{Cr}^{3+} + 7\text{H}_2\text{O}(l)\) | 1.36 | |
| \(\text{CrO}_4^{2-} + 4\text{H}_2\text{O}(l) + 3e^- \rightleftharpoons \text{Cr(OH)}_4^- + 4\text{OH}^-\) | –0.13 in 1 M NaOH |
| Cobalt | E (V) | Eo ́ (V) |
|---|---|---|
| \(\text{Co}^{2+} + 2e^- \rightleftharpoons \text{Co}(s)\) | –0.277 | |
| \(\text{Co}^{3+} + 3e^- \rightleftharpoons \text{Co}(s)\) | 1.92 | |
| \(\text{Co(NH}_3)_6^{3+} + e^- \rightleftharpoons \text{Co(NH}_3)_6^{2+}\) | 0.1 | |
| \(\text{Co(OH)}_3(s) + e^- \rightleftharpoons \text{Co(OH)}_2(s) + \text{OH}^-\) | 0.17 | |
| \(\text{Co(OH)}_2(s) + 2e^- \rightleftharpoons \text{Co}(s) + 2\text{OH}^-\) | –0.746 |
| Copper | E (V) | Eo ́ (V) |
|---|---|---|
| \(\text{Cu}^+ + e^- \rightleftharpoons \text{Cu}(s)\) | 0.520 | |
| \(\text{Cu}^{2+} + e^- \rightleftharpoons \text{Cu}^+\) | 0.159 | |
| \(\text{Cu}^{2+} + 2e^- \rightleftharpoons \text{Cu}(s)\) | 0.3419 | |
| \(\text{Cu}^{2+} + \text{I}^- + e^- \rightleftharpoons \text{CuI}(s)\) | 0.86 | |
| \(\text{Cu}^{2+} + \text{Cl}^- + e^- \rightleftharpoons \text{CuCl}(s)\) | 0.559 |
| Fluorine | E (V) | Eo ́ (V) |
|---|---|---|
| \(\text{F}_2(g) + 2\text{H}^+ + 2e^- \rightleftharpoons 2\text{HF}(g)\) | 3.053 | |
| \(\text{F}_2(g) + 2e^- \rightleftharpoons 2\text{F}^-\) | 2.87 |
| Gallium | E (V) | Eo ́ (V) |
|---|---|---|
| \(\text{Ga}^{3+} + 3e^- \rightleftharpoons \text{Ga}(s)\) | –0.529 |
| Gold | E (V) | Eo ́ (V) |
|---|---|---|
| \(\text{Au}^+ + e^- \rightleftharpoons \text{Au}(s)\) | 1.83 | |
| \(\text{Au}^{3+} + 2e^- \rightleftharpoons \text{Au}^+\) | 1.36 | |
| \(\text{Au}^{3+} + 3e^- \rightleftharpoons \text{Au}(s)\) | 1.52 | |
| \(\text{AuCl}_4^- + 3e^- \rightleftharpoons \text{Au}(s) + 4\text{Cl}^-\) | 1.002 |
| Hydrogen | E (V) | Eo ́ (V) |
|---|---|---|
| \(2\text{H}^+ + 2e^- \rightleftharpoons \text{H}_2 (g)\) | 0.00000 | |
| \(\text{H}_2\text{O}(l) + e^- \rightleftharpoons \frac{1}{2} \text{H}_2(g) + \text{OH}^-\) | –0.828 |
| Iodine | E (V) | Eo ́ (V) |
|---|---|---|
| \(\text{I}_2(s) + 2e^- \rightleftharpoons 2\text{I}^-\) | 0.5355 |
| Iodine | E (V) | Eo ́ (V) |
|---|---|---|
| \(\text{I}_3^- + 2e^- \rightleftharpoons 3\text{I}^-\) | 0.536 | |
| \(\text{HIO} + \text{H}^+ + 2e^- \rightleftharpoons \text{I}^- + \text{H}_2\text{O}(l)\) | 0.985 | |
| \(\text{IO}_3^- + 6\text{H}^+ + 5e^- \rightleftharpoons \frac{1}{2} \text{I}_2(s) + 3\text{H}_2\text{O}(l)\) | 1.195 | |
| \(\text{IO}_3^- + 3\text{H}_2\text{O}(l) + 6e^- \rightleftharpoons \text{I}^- +6\text{OH}^-\) | 0.257 |
| Iron | E (V) | Eo ́ (V) |
|---|---|---|
| \(\text{Fe}^{2+} + 2e^- \rightleftharpoons \text{Fe}(s)\) | –0.44 | |
| \(\text{Fe}^{3+} + 3e^- \rightleftharpoons \text{Fe}(s)\) | –0.037 | |
| \(\text{Fe}^{3+} + e^- \rightleftharpoons \text{Fe}^{2+}\) | 0.771 |
0.70 in 1 M HCl 0.767 in 1 M HClO4 0.746 in 1 M HNO3 0.68 in 1 M H2SO4 0.44 in 0.3 M H3PO4 |
| \(\text{Fe(CN)}_6^{3-} + e^- \rightleftharpoons \text{Fe(CN)}_6^{4-}\) | 0.356 | |
| \(\text{Fe(phen)}_3^{3+} + e^- \rightleftharpoons \text{Fe(phen)}_3^{2+}\) | 1.147 |
| Lanthanum | E (V) | Eo ́ (V) |
|---|---|---|
| \(\text{La}^{3+} + 3e^- \rightleftharpoons \text{La}(s)\) | –2.38 |
| Lead | E (V) | Eo ́ (V) |
|---|---|---|
| \(\text{Pb}^{2+} + 2e^- \rightleftharpoons \text{Pb}(s)\) | –0.126 | |
| \(\text{PbO}_2(s) + 4\text{H}^+ + 2e^- \rightleftharpoons \text{Pb}^{2+} + 2\text{H}_2\text{O}(l)\) | 1.46 | |
| \(\text{PbO}_2(s) + \text{SO}_4^{2-} + 4\text{H}^+ + 2e^- \rightleftharpoons \text{PbSO}_4(s) + 2\text{H}_2\text{O}(l)\) | 1.690 | |
| \(\text{PbSO}_4(s) + 2e^- \rightleftharpoons \text{Pb}(s) + \text{SO}_4^{2-}\) | –0.356 |
| Lithium | E (V) | Eo ́ (V) |
|---|---|---|
| \(\text{Li}^+ + e^- \rightleftharpoons \text{Li}(s)\) | –3.040 |
| Magnesium | E (V) | Eo ́ (V) |
|---|---|---|
| \(\text{Mg}^{2+} + 2e^- \rightleftharpoons \text{Mg}(s)\) | –2.356 | |
| \(\text{Mg(OH)}_2(s) + 2e^- \rightleftharpoons \text{Mg}(s) + 2\text{OH}^-\) | –2.687 |
| Manganese | E (V) | Eo ́ (V) |
|---|---|---|
| \(\text{Mn}^{2+} + 2e^- \rightleftharpoons \text{Mn}(s)\) | –1.17 | |
| \(\text{Mn}^{3+} + e^- \rightleftharpoons \text{Mn}^{2+}\) | 1.5 | |
| \(\text{MnO}_2(s) + 4\text{H}^+ + 2e^- \rightleftharpoons \text{Mn}^{2+} + 2\text{H}_2\text{O}(l)\) | 1.23 | |
| \(\text{MnO}_4^- + 4\text{H}^+ +3e^- \rightleftharpoons \text{MnO}_2(s) + 2\text{H}_2\text{O}(l)\) | 1.70 | |
| \(\text{MnO}_4^- + 8\text{H}^+ + 5e^- \rightleftharpoons \text{Mn}^{2+} + 4\text{H}_2\text{O}(l)\) | 1.51 | |
| \(\text{MnO}_4^- + 2\text{H}_2\text{O}(l) + 3e^- \rightleftharpoons \text{MnO}_2(s) + 4\text{OH}^-\) | 0.60 |
| Mercury | E (V) | Eo ́ (V) |
|---|---|---|
| \(\text{Hg}^{2+} + 2e^- \rightleftharpoons \text{Hg}(l)\) | 0.8535 | |
| \(2\text{Hg}^{2+} +2e^- \rightleftharpoons \text{Hg}_2^{2+}\) | 0.911 |
| Mercury | E (V) | Eo ́ (V) |
|---|---|---|
| \(\text{Hg}_2^{2+} + 2e^- \rightleftharpoons 2\text{Hg}(l)\) | 0.7960 | |
| \(\text{Hg}_2\text{Cl}_2(s) + 2e^- \rightleftharpoons 2\text{Hg}(l) + 2\text{Cl}^-\) | 0.2682 | |
| \(\text{HgO}(s) + 2\text{H}^+ + 2e^- \rightleftharpoons \text{Hg}(l) + \text{H}_2\text{O}(l)\) | 0.926 | |
| \(\text{Hg}_2\text{Br}_2(s) + 2e^- \rightleftharpoons 2\text{Hg}(l) + 2\text{Br}^-\) | 1.392 | |
| \(\text{Hg}_2\text{I}_2(s) + 2e^- \rightleftharpoons 2\text{Hg}(l) + 2\text{I}^-\) | –0.0405 |
| Molybdenum | E (V) | Eo ́ (V) |
|---|---|---|
| \(\text{Mo}^{3+} + 3e^- \rightleftharpoons \text{Mo}(s)\) | –0.2 | |
| \(\text{MoO}_2(s) + 4\text{H}^+ + 4e^- \rightleftharpoons \text{Mo}(s) + 2\text{H}_2\text{O}(l)\) | –0.152 | |
| \(\text{MoO}_4^{2-} + 4\text{H}_2\text{O}(l) + 6e^- \rightleftharpoons \text{Mo}(s) + 8\text{OH}^-\) | –0.913 |
| Nickel | E (V) | Eo ́ (V) |
|---|---|---|
| \(\text{Ni}^{2+} + 2e^- \rightleftharpoons \text{Ni}(s)\) | –0.257 | |
| \(\text{Ni(OH)}_2(s) + 2e^- \rightleftharpoons \text{Ni}(s) + 2\text{OH}^-\) | –0.72 | |
| \(\text{Ni(NH}_3)_6^{2+} + 2e^- \rightleftharpoons \text{Ni}(s) + 6\text{NH}_3\) | –0.49 |
| Nitrogen | E (V) | Eo ́ (V) |
|---|---|---|
| \(\text{N}_2(g) + 5\text{H}^+ + 4e^- \rightleftharpoons \text{N}_2\text{H}_5^+\) | –0.23 | |
| \(\text{N}_2\text{O}(g) + 2\text{H}^+ + 2e^- \rightleftharpoons \text{N}_2(g) + \text{H}_2\text{O}(l)\) | 1.77 | |
| \(2\text{NO}(g) + 2\text{H}^+ + 2e^- \rightleftharpoons \text{N}_2\text{O}(g) + \text{H}_2\text{O}(l)\) | 1.59 | |
| \(\text{HNO}_2 + \text{H}^+ + e^- \rightleftharpoons \text{NO}(g) + \text{H}_2\text{O}(l)\) | 0.996 | |
| \(2\text{HNO}_2 + 4\text{H}^+ + 4e^- \rightleftharpoons \text{N}_2\text{O}(g) + 3\text{H}_2\text{O}(l)\) | 1.297 | |
| \(\text{NO}_3^- + 3\text{H}^+ + 2e^- \rightleftharpoons \text{HNO}_2 + \text{H}_2\text{O}(l)\) | 0.94 |
| Oxygen | E (V) | Eo ́ (V) |
|---|---|---|
| \(\text{O}_2(g) + 2\text{H}^+ + 2e^- \rightleftharpoons \text{H}_2\text{O}_2\) | 0.695 | |
| \(\text{O}_2(g) + 4\text{H}^+ + 4e^- \rightleftharpoons 2\text{H}_2\text{O}(l)\) | 1.229 | |
| \(\text{H}_2\text{O}_2 + 2\text{H}^+ + 2e^- \rightleftharpoons 2\text{H}_2\text{O}(l)\) | 1.763 | |
| \(\text{O}_2(g) + 2\text{H}_2\text{O}(l) + 4e^- \rightleftharpoons 4\text{OH}^-\) | 0.401 | |
| \(\text{O}_3(g) + 2\text{H}^+ + 2e^- \rightleftharpoons \text{O}_2(g) + \text{H}_2\text{O}(l)\) | 2.07 |
| Phosphorous | E (V) | Eo ́ (V) |
|---|---|---|
| \(\text{P}(s, white) + 3\text{H}^+ + 3e^- \rightleftharpoons \text{PH}_3(g)\) | –0.063 | |
| \(\text{H}_3\text{PO}_3 + 2\text{H}^+ + 2e^- \rightleftharpoons \text{H}_3\text{PO}_2 + \text{H}_2\text{O}(l)\) | –0.499 | |
| \(\text{H}_3\text{PO}_4 + 2\text{H}^+ + 2e^- \rightleftharpoons \text{H}_3\text{PO}_3 + \text{H}_2\text{O}(l)\) | –0.276 |
| Platinum | E (V) | Eo ́ (V) |
|---|---|---|
| \(\text{Pt}^{2+} + 2e^- \rightleftharpoons \text{Pt}(s)\) | 1.188 | |
| \(\text{PtCl}_4^{2-} + 2e^- \rightleftharpoons \text{Pt}(s) + 4\text{Cl}^-\) | 0.758 |
| Potasium | E (V) | Eo ́ (V) |
|---|---|---|
| \(\text{K}^+ + e^- \rightleftharpoons \text{K}(s)\) | –2.924 |
| Ruthenium | E (V) | Eo ́ (V) |
|---|---|---|
| \(\text{Ru}^{3+} + 3e^- \rightleftharpoons \text{Ru}(s)\) | 0.249 | |
| \(\text{RuO}_2(s) + 4\text{H}^+ + 4e^- \rightleftharpoons \text{Ru}(s) + 2\text{H}_2\text{O}(l)\) | 0.68 | |
| \(\text{Ru(NH}_3)_6^{3+} + e^- \rightleftharpoons \text{Ru(NH}_3)_6^{2+}\) | 0.10 | |
| \(\text{Ru(CN)}_6^{3-} + e^- \rightleftharpoons \text{Ru(CN)}_6^{4-}\) | 0.86 |
| Selenium | E (V) | Eo ́ (V) |
|---|---|---|
| \(\text{Se}(s) + 2e^- \rightleftharpoons \text{Se}^{2-}\) | –0.67 in 1 M NaOH | |
| \(\text{Se}(s) + 2\text{H}^+ + 2e^- \rightleftharpoons \text{H}_2\text{Se}(g)\) | –0.115 | |
| \(\text{H}_2\text{SeO}_3 + 4\text{H}^+ + 4e^- \rightleftharpoons \text{Se}(s) + 3\text{H}_2\text{O}(l)\) | 0.74 | |
| \(\text{SeO}_4^{3-} + 4\text{H}^+ + e^- \rightleftharpoons \text{H}_2\text{SeO}_3 + \text{H}_2\text{O}(l)\) | 1.151 |
| Silicon | E (V) | Eo ́ (V) |
|---|---|---|
| \(\text{SiF}_6^{2-} + 4e^- \rightleftharpoons \text{Si}(s) + 6\text{F}^-\) | –1.37 | |
| \(\text{SiO}_2(s) + 4\text{H}^+ + 4e^- \rightleftharpoons \text{Si}(s) + 2\text{H}_2\text{O}(l)\) | –0.909 | |
| \(\text{SiO}_2(s) + 8\text{H}^+ + 8e^- \rightleftharpoons \text{SiH}_4(g) + 2\text{H}_2\text{O}(l)\) | –0.516 |
| Silver | E (V) | Eo ́ (V) |
|---|---|---|
| \(\text{Ag}^+ + e^- \rightleftharpoons \text{Ag}(s)\) | 0.7996 | |
| \(\text{AgBr}(s) + e^- \rightleftharpoons \text{Ag}(s) + \text{Br}^-\) | 0.071 | |
| \(\text{Ag}_2\text{C}_2\text{O}_4(s) + 2e^- \rightleftharpoons 2\text{Ag}(s) + \text{C}_2\text{O}_4^{2-}\) | 0.47 | |
| \(\text{AgCl}(s) + e^- \rightleftharpoons \text{Ag}(s) + \text{Cl}^-\) | 0.2223 | |
| \(\text{AgI}(s) + e^- \rightleftharpoons \text{Ag}(s) + \text{I}^-\) | –0.152 | |
| \(\text{Ag}_2\text{S}(s) + 2e^- \rightleftharpoons 2\text{Ag}(s) + \text{S}^{2-}\) | –0.71 | |
| \(\text{Ag(NH}_3)_2^+ + e^- \rightleftharpoons \text{Ag}(s) + 2\text{NH}_3\) | –0.373 |
| Sodium | E (V) | Eo ́ (V) |
|---|---|---|
| \(\text{Na}^+ + e^- \rightleftharpoons \text{Na}(s)\) | –2.713 |
| Strontium | E (V) | Eo ́ (V) |
|---|---|---|
| \(\text{Sr}^{2+} + 2e^- \rightleftharpoons \text{Sr}(s)\) | –2.89 |
| Sulfur | E (V) | Eo ́ (V) |
|---|---|---|
| \(\text{S}(s) + 2e^- \rightleftharpoons \text{S}^{2-}\) | –0.407 | |
| \(\text{S}(s) + 2\text{H}^+ + 2e^- \rightleftharpoons \text{H}_2\text{S}(g)\) | 0.144 | |
| \(\text{S}_2\text{O}_6^{2-} + 4\text{H}^+ + 2e^- \rightleftharpoons 2\text{H}_2\text{SO}_3\) | 0.569 | |
| \(\text{S}_2\text{O}_8^{2-} + 2e^- \rightleftharpoons 2\text{SO}_4^{2-}\) | 1.96 | |
| \(\text{S}_4\text{O}_6^{2-} + 2e^- \rightleftharpoons 2\text{S}_2\text{O}_3^{2-}\) | 0.080 | |
| \(2\text{SO}_3^{2-} + 2\text{H}_2\text{O}(l) + 2e^- \rightleftharpoons \text{S}_2\text{O}_4^{2-} + 4\text{OH}^-\) | –1.13 | |
| \(2\text{SO}_3^{2-} + 3\text{H}_2\text{O}(l) + 4e^- \rightleftharpoons \text{S}_2\text{O}_3^{2-} + 6\text{OH}^-\) | –0.576 in 1 M NaOH | |
| \(2\text{SO}_4^{2-} + 4\text{H}^+ + 2e^- \rightleftharpoons \text{S}_2\text{O}_6^{2-} + 2\text{H}_2\text{O}(l)\) | –0.25 | |
| \(\text{SO}_4^{2-} + \text{H}_2\text{O}(l) + 2e^- \rightleftharpoons \text{SO}_3^{2-} + 2\text{OH}^-\) | –0.936 | |
| \(\text{SO}_4^{2-} + 4\text{H}^+ + 2e^- \rightleftharpoons \text{H}_2\text{SO}_3 + \text{H}_2\text{O}(l)\) | 0.172 |
| Thallium | E (V) | Eo ́ (V) |
|---|---|---|
| \(\text{Tl}^{3+} + 2e^- \rightleftharpoons \text{Tl}^+\) |
1.25 in 1 M HClO4 0.77 in 1 M HCl |
|
| \(\text{Tl}^{3+} + 3e^- \rightleftharpoons \text{Tl}(s)\) | 0.742 |
| Tin | E (V) | Eo ́ (V) |
|---|---|---|
| \(\text{Sn}^{2+} + 2e^- \rightleftharpoons \text{Sn}(s)\) | –0.19 in 1 M HCl | |
| \(\text{Sn}^{4+} + 2e^- \rightleftharpoons \text{Sn}^{2+}\) | 0.154 | 0.139 in 1 M HCl |
| Titanium | E (V) | Eo ́ (V) |
|---|---|---|
| \(\text{Ti}^{2+} + 2e^- \rightleftharpoons \text{Ti}(s)\) | –0.163 | |
| \(\text{Ti}^{3+} + e^- \rightleftharpoons \text{Ti}^{2+}\) | –0.37 |
| Tungsten | E (V) | Eo ́ (V) |
|---|---|---|
| \(\text{WO}_2(s) + 4\text{H}^+ + 4e^- \rightleftharpoons \text{W}(s) + 2\text{H}_2\text{O}(l)\) | –0.119 | |
| \(\text{WO}_3(s) + 6\text{H}^+ + 6e^- \rightleftharpoons \text{W}(s) + 3\text{H}_2\text{O}(l)\) | –0.090 |
| Uranium | E (V) | Eo ́ (V) |
|---|---|---|
| \(\text{U}^{3+} + 3e^- \rightleftharpoons \text{U}(s)\) | –1.66 | |
| \(\text{U}^{4+} + e^- \rightleftharpoons \text{U}^{3+}\) | –0.52 | |
| \(\text{UO}_2^+ + 4\text{H}^+ + e^- \rightleftharpoons \text{U}^{4+} + 2\text{H}_2\text{O}(l)\) | 0.27 | |
| \(\text{UO}_2^{2+} + e^- \rightleftharpoons \text{UO}_2^+\) | 0.16 | |
| \(\text{UO}_2^{2+} + 4\text{H}^+ + 2e^- \rightleftharpoons \text{U}^{4+} + 2\text{H}_2\text{O}(l)\) | 0.327 |
| Vanadium | E (V) | Eo ́ (V) |
|---|---|---|
| \(\text{V}^{2+} + 2e^- \rightleftharpoons \text{V}(s)\) | –1.13 | |
| \(\text{V}^{3+} + e^- \rightleftharpoons \text{V}^{2+}\) | –0.255 | |
| \(\text{VO}^{2+} + 2\text{H}^+ + e^- \rightleftharpoons \text{V}^{3+} + \text{H}_2\text{O}(l)\) | 0.337 | |
| \(\text{VO}_2^{+} + 2\text{H}^+ + e^- \rightleftharpoons \text{VO}^{2+} + \text{H}_2\text{O}(l)\) | 1.000 |
| Zinc | E (V) | Eo ́ (V) |
|---|---|---|
| \(\text{Zn}^{2+} + 2e^- \rightleftharpoons \text{Zn}(s)\) | –0.7618 | |
| \(\text{Zn(OH)}_4^{2-} + 2e^- \rightleftharpoons \text{Zn}(s) + 4\text{OH}^-\) | –1.285 | |
| \(\text{Zn(NH}_3)_4^{2+} + 2e^- \rightleftharpoons \text{Zn}(s) + 4\text{NH}_3\) | –1.04 | |
| \(\text{Zn(CN)}_4^{2-} + 2e^- \rightleftharpoons \text{Zn}(s) + 4\text{CN}^-\) | –1.34 |
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 | \(E_{1/2}\) (volts vs. SCE) | Matrix |
|---|---|---|
| \(\ce{Al^{3+}}(aq) + \ce{3 e-} \ce{<=>} \ce{Al}(s)\) | –0.5 | 0.2 M acetate (pH 4.5–4.7) |
| \(\ce{Cd^{2+}}(aq) + \ce{2 e-} \ce{<=>} \ce{Cd}(s)\) | –0.6 |
0.1 M KCl 0.050 M H2SO4 1 M HNO3 |
| \(\ce{Cr^{3+}}(aq) + \ce{3 e-} \ce{<=>} \ce{Cr}(s)\) |
–0.35 \((+3 \ce{->} +2)\) –1.70 \((+2 \ce{->} 0)\) |
1 M NH4Cl plus 1 M NH3 1 M NH4+/NH3 buffer (pH 8–9) |
| \(\ce{Co^{3+}}(aq)+ \ce{3 e-} \ce{<=>} \ce{Co}(s)\) |
–0.5 \((+3 \ce{->} +2)\) –1.3 \((+2 \ce{->} 0)\) |
1 M NH4Cl plus 1 M NH3 |
| \(\ce{Co^{2+}}(aq) + \ce{2 e-} \ce{<=>} \ce{Co}(s)\) | –1.03 | 1 M KSCN |
| \(\ce{Cu^{2+}}(aq) + \ce{2 e-} \ce{<=>} \ce{Cu}(s)\) |
0.04 –0.22 |
0.1 M KSCN 0.1 M NH4ClO4 1 M Na2SO4 0.5 M potassium citrate (pH 7.5) |
| \(\ce{Fe^{3+}}(aq) + \ce{3 e-} \ce{<=>} \ce{Fe}(s)\) |
–0.17 \((+3 \ce{->} +2)\) –1.52 \((+2 \ce{->} 0)\) |
0.5 M sodium tartrate (pH 5.8) |
| \(\ce{Fe^{3+}}(aq) + \ce{e-} \ce{<=>} \ce{Fe^{2+}}(aq)\) | –0.27 | 0.2 M Na2C2O4 (pH < 7.9) |
| \(\ce{Pb^{2+}}(aq) + \ce{2 e-} \ce{<=>} \ce{Pb}(s)\) |
–0.405 –0.435 |
1 M HNO3 1 M KCl |
| \(\ce{Mn^{2+}}(aq) + \ce{2 e-} \ce{<=>} \ce{Mn}(s)\) | –1.65 | 1 M NH4Cl plus 1 M NH3 |
| \(\ce{Ni^{2+}}(aq) + \ce{2 e-} \ce{<=>} \ce{Ni}(s)\) |
–0.70 –1.09 |
1 M KSCN 1 M NH4Cl plus 1 M NH3 |
| \(\ce{Zn^{2+}}(aq) + \ce{2 e-} \ce{<=>} \ce{Zn}(s)\) |
–0.995 –1.33 |
0.1 M KCl 1 M NH4Cl plus 1 M NH3 |