F Fluorine/fluoride F X 2 + 2 e X − ⇌ 2 F X − \ce{F2 + 2e- <=> 2F-} F X 2 + 2 e X − 2 F X − 2 2.866 — Fe Ferrate(VI)/iron(III) F e O X 4 X 2 − + 8 H X + + 3 e X − ⇌ F e X 3 + + 4 H X 2 O \ce{FeO4^2- + 8H+ + 3e- <=> Fe^3+ + 4H2O} FeO X 4 X 2 − + 8 H X + + 3 e X − Fe X 3 + + 4 H X 2 O 3 2.2 acid O Ozone/oxygen O X 3 + 2 H X + + 2 e X − ⇌ O X 2 + H X 2 O \ce{O3 + 2H+ + 2e- <=> O2 + H2O} O X 3 + 2 H X + + 2 e X − O X 2 + H X 2 O 2 2.076 acid S Peroxodisulfate/sulfate S X 2 O X 8 X 2 − + 2 e X − ⇌ 2 S O X 4 X 2 − \ce{S2O8^2- + 2e- <=> 2SO4^2-} S X 2 O X 8 X 2 − + 2 e X − 2 SO X 4 X 2 − 2 2.01 — Co Cobalt(III)/cobalt(II) C o X 3 + + e X − ⇌ C o X 2 + \ce{Co^3+ + e- <=> Co^2+} Co X 3 + + e X − Co X 2 + 1 1.92 — O Hydrogen peroxide/water H X 2 O X 2 + 2 H X + + 2 e X − ⇌ 2 H X 2 O \ce{H2O2 + 2H+ + 2e- <=> 2H2O} H X 2 O X 2 + 2 H X + + 2 e X − 2 H X 2 O 2 1.776 acid N Nitrous oxide/nitrogen N X 2 O + 2 H X + + 2 e X − ⇌ N X 2 + H X 2 O \ce{N2O + 2H+ + 2e- <=> N2 + H2O} N X 2 O + 2 H X + + 2 e X − N X 2 + H X 2 O 2 1.766 acid Ce Cerium(IV)/cerium(III) C e X 4 + + e X − ⇌ C e X 3 + \ce{Ce^4+ + e- <=> Ce^3+} Ce X 4 + + e X − Ce X 3 + 1 1.72 — Pb Lead dioxide/lead sulfate (lead–acid positive plate) P b O X 2 + S O X 4 X 2 − + 4 H X + + 2 e X − ⇌ P b S O X 4 + 2 H X 2 O \ce{PbO2 + SO4^2- + 4H+ + 2e- <=> PbSO4 + 2H2O} PbO X 2 + SO X 4 X 2 − + 4 H X + + 2 e X − PbSO X 4 + 2 H X 2 O 2 1.6913 acid Mn Permanganate/manganese dioxide M n O X 4 X − + 4 H X + + 3 e X − ⇌ M n O X 2 + 2 H X 2 O \ce{MnO4- + 4H+ + 3e- <=> MnO2 + 2H2O} MnO X 4 X − + 4 H X + + 3 e X − MnO X 2 + 2 H X 2 O 3 1.679 acid Cl Chlorous acid/hypochlorous acid H C l O X 2 + 2 H X + + 2 e X − ⇌ H C l O + H X 2 O \ce{HClO2 + 2H+ + 2e- <=> HClO + H2O} HClO X 2 + 2 H X + + 2 e X − HClO + H X 2 O 2 1.645 acid Cl Hypochlorous acid/chlorine 2 H C l O + 2 H X + + 2 e X − ⇌ C l X 2 + 2 H X 2 O \ce{2HClO + 2H+ + 2e- <=> Cl2 + 2H2O} 2 HClO + 2 H X + + 2 e X − Cl X 2 + 2 H X 2 O 2 1.611 acid N Nitric oxide/nitrous oxide 2 N O + 2 H X + + 2 e X − ⇌ N X 2 O + H X 2 O \ce{2NO + 2H+ + 2e- <=> N2O + H2O} 2 NO + 2 H X + + 2 e X − N X 2 O + H X 2 O 2 1.591 acid Mn Manganese(III)/manganese(II) M n X 3 + + e X − ⇌ M n X 2 + \ce{Mn^3+ + e- <=> Mn^2+} Mn X 3 + + e X − Mn X 2 + 1 1.5415 — Mn Permanganate/manganese(II) M n O X 4 X − + 8 H X + + 5 e X − ⇌ M n X 2 + + 4 H X 2 O \ce{MnO4- + 8H+ + 5e- <=> Mn^2+ + 4H2O} MnO X 4 X − + 8 H X + + 5 e X − Mn X 2 + + 4 H X 2 O 5 1.507 acid Au Gold(III)/gold A u X 3 + + 3 e X − ⇌ A u \ce{Au^3+ + 3e- <=> Au} Au X 3 + + 3 e X − Au 3 1.498 — Mn Manganese(III) oxide/manganese(II) M n X 2 O X 3 + 6 H X + + 2 e X − ⇌ 2 M n X 2 + + 3 H X 2 O \ce{Mn2O3 + 6H+ + 2e- <=> 2Mn^2+ + 3H2O} Mn X 2 O X 3 + 6 H X + + 2 e X − 2 Mn X 2 + + 3 H X 2 O 2 1.485 acid Pb Lead dioxide/lead(II) P b O X 2 + 4 H X + + 2 e X − ⇌ P b X 2 + + 2 H X 2 O \ce{PbO2 + 4H+ + 2e- <=> Pb^2+ + 2H2O} PbO X 2 + 4 H X + + 2 e X − Pb X 2 + + 2 H X 2 O 2 1.455 acid Cl Chlorate/chloride C l O X 3 X − + 6 H X + + 6 e X − ⇌ C l X − + 3 H X 2 O \ce{ClO3- + 6H+ + 6e- <=> Cl- + 3H2O} ClO X 3 X − + 6 H X + + 6 e X − Cl X − + 3 H X 2 O 6 1.451 acid N Hydroxylammonium/hydrazinium 2 N H X 3 O H X + + H X + + 2 e X − ⇌ N X 2 H X 5 X + + 2 H X 2 O \ce{2NH3OH+ + H+ + 2e- <=> N2H5+ + 2H2O} 2 NH X 3 OH X + + H X + + 2 e X − N X 2 H X 5 X + + 2 H X 2 O 2 1.42 acid Cr Dichromate/chromium(III) C r X 2 O X 7 X 2 − + 14 H X + + 6 e X − ⇌ 2 C r X 3 + + 7 H X 2 O \ce{Cr2O7^2- + 14H+ + 6e- <=> 2Cr^3+ + 7H2O} Cr X 2 O X 7 X 2 − + 14 H X + + 6 e X − 2 Cr X 3 + + 7 H X 2 O 6 1.36 acid Cl Chlorine/chloride C l X 2 + 2 e X − ⇌ 2 C l X − \ce{Cl2 + 2e- <=> 2Cl-} Cl X 2 + 2 e X − 2 Cl X − 2 1.35827 — N Hydrazinium/ammonium N X 2 H X 5 X + + 3 H X + + 2 e X − ⇌ 2 N H X 4 X + \ce{N2H5+ + 3H+ + 2e- <=> 2NH4+} N X 2 H X 5 X + + 3 H X + + 2 e X − 2 NH X 4 X + 2 1.275 acid O Oxygen/water (acid) O X 2 + 4 H X + + 4 e X − ⇌ 2 H X 2 O \ce{O2 + 4H+ + 4e- <=> 2H2O} O X 2 + 4 H X + + 4 e X − 2 H X 2 O 4 1.229 acid Mn Manganese dioxide/manganese(II) M n O X 2 + 4 H X + + 2 e X − ⇌ M n X 2 + + 2 H X 2 O \ce{MnO2 + 4H+ + 2e- <=> Mn^2+ + 2H2O} MnO X 2 + 4 H X + + 2 e X − Mn X 2 + + 2 H X 2 O 2 1.224 acid Cl Chlorate/chlorous acid C l O X 3 X − + 3 H X + + 2 e X − ⇌ H C l O X 2 + H X 2 O \ce{ClO3- + 3H+ + 2e- <=> HClO2 + H2O} ClO X 3 X − + 3 H X + + 2 e X − HClO X 2 + H X 2 O 2 1.214 acid I Iodate/iodine 2 I O X 3 X − + 12 H X + + 10 e X − ⇌ I X 2 + 6 H X 2 O \ce{2IO3- + 12H+ + 10e- <=> I2 + 6H2O} 2 IO X 3 X − + 12 H X + + 10 e X − I X 2 + 6 H X 2 O 10 1.195 acid Cl Perchlorate/chlorate C l O X 4 X − + 2 H X + + 2 e X − ⇌ C l O X 3 X − + H X 2 O \ce{ClO4- + 2H+ + 2e- <=> ClO3- + H2O} ClO X 4 X − + 2 H X + + 2 e X − ClO X 3 X − + H X 2 O 2 1.189 acid Pt Platinum(II)/platinum P t X 2 + + 2 e X − ⇌ P t \ce{Pt^2+ + 2e- <=> Pt} Pt X 2 + + 2 e X − Pt 2 1.18 — Br Bromine/bromide B r X 2 + 2 e X − ⇌ 2 B r X − \ce{Br2 + 2e- <=> 2Br-} Br X 2 + 2 e X − 2 Br X − 2 1.066 — N Dinitrogen tetroxide/nitrous acid N X 2 O X 4 + 2 H X + + 2 e X − ⇌ 2 H N O X 2 \ce{N2O4 + 2H+ + 2e- <=> 2HNO2} N X 2 O X 4 + 2 H X + + 2 e X − 2 HNO X 2 2 1.065 acid N Nitrous acid/nitric oxide H N O X 2 + H X + + e X − ⇌ N O + H X 2 O \ce{HNO2 + H+ + e- <=> NO + H2O} HNO X 2 + H X + + e X − NO + H X 2 O 1 0.983 acid N Nitrate/nitric oxide N O X 3 X − + 4 H X + + 3 e X − ⇌ N O + 2 H X 2 O \ce{NO3- + 4H+ + 3e- <=> NO + 2H2O} NO X 3 X − + 4 H X + + 3 e X − NO + 2 H X 2 O 3 0.957 acid N Nitrate/nitrous acid N O X 3 X − + 3 H X + + 2 e X − ⇌ H N O X 2 + H X 2 O \ce{NO3- + 3H+ + 2e- <=> HNO2 + H2O} NO X 3 X − + 3 H X + + 2 e X − HNO X 2 + H X 2 O 2 0.934 acid Hg Mercury(II)/mercury(I) 2 H g X 2 + + 2 e X − ⇌ H g X 2 X 2 + \ce{2Hg^2+ + 2e- <=> Hg2^2+} 2 Hg X 2 + + 2 e X − Hg X 2 X 2 + 2 0.92 — Hg Mercury(II)/mercury H g X 2 + + 2 e X − ⇌ H g \ce{Hg^2+ + 2e- <=> Hg} Hg X 2 + + 2 e X − Hg 2 0.851 — N Nitrate/dinitrogen tetroxide 2 N O X 3 X − + 4 H X + + 2 e X − ⇌ N X 2 O X 4 + 2 H X 2 O \ce{2NO3- + 4H+ + 2e- <=> N2O4 + 2H2O} 2 NO X 3 X − + 4 H X + + 2 e X − N X 2 O X 4 + 2 H X 2 O 2 0.803 acid Ag Silver ion/silver A g X + + e X − ⇌ A g \ce{Ag+ + e- <=> Ag} Ag X + + e X − Ag 1 0.7996 — Hg Mercury(I)/mercury H g X 2 X 2 + + 2 e X − ⇌ 2 H g \ce{Hg2^2+ + 2e- <=> 2Hg} Hg X 2 X 2 + + 2 e X − 2 Hg 2 0.7973 — Fe Iron(III)/iron(II) F e X 3 + + e X − ⇌ F e X 2 + \ce{Fe^3+ + e- <=> Fe^2+} Fe X 3 + + e X − Fe X 2 + 1 0.771 — O Oxygen/hydrogen peroxide O X 2 + 2 H X + + 2 e X − ⇌ H X 2 O X 2 \ce{O2 + 2H+ + 2e- <=> H2O2} O X 2 + 2 H X + + 2 e X − H X 2 O X 2 2 0.695 acid Mn Manganate/manganese dioxide (base) M n O X 4 X 2 − + 2 H X 2 O + 2 e X − ⇌ M n O X 2 + 4 O H X − \ce{MnO4^2- + 2H2O + 2e- <=> MnO2 + 4OH-} MnO X 4 X 2 − + 2 H X 2 O + 2 e X − MnO X 2 + 4 OH X − 2 0.6 base Mn Permanganate/manganese dioxide (base) M n O X 4 X − + 2 H X 2 O + 3 e X − ⇌ M n O X 2 + 4 O H X − \ce{MnO4- + 2H2O + 3e- <=> MnO2 + 4OH-} MnO X 4 X − + 2 H X 2 O + 3 e X − MnO X 2 + 4 OH X − 3 0.595 base Mn Permanganate/manganate M n O X 4 X − + e X − ⇌ M n O X 4 X 2 − \ce{MnO4- + e- <=> MnO4^2-} MnO X 4 X − + e X − MnO X 4 X 2 − 1 0.558 — I Triiodide/iodide I X 3 X − + 2 e X − ⇌ 3 I X − \ce{I3- + 2e- <=> 3I-} I X 3 X − + 2 e X − 3 I X − 2 0.536 — I Iodine/iodide I X 2 + 2 e X − ⇌ 2 I X − \ce{I2 + 2e- <=> 2I-} I X 2 + 2 e X − 2 I X − 2 0.5355 — Cu Copper(I)/copper C u X + + e X − ⇌ C u \ce{Cu+ + e- <=> Cu} Cu X + + e X − Cu 1 0.521 — O Oxygen/hydroxide (base) O X 2 + 2 H X 2 O + 4 e X − ⇌ 4 O H X − \ce{O2 + 2H2O + 4e- <=> 4OH-} O X 2 + 2 H X 2 O + 4 e X − 4 OH X − 4 0.401 base Cl Perchlorate/chlorate (base) C l O X 4 X − + H X 2 O + 2 e X − ⇌ C l O X 3 X − + 2 O H X − \ce{ClO4- + H2O + 2e- <=> ClO3- + 2OH-} ClO X 4 X − + H X 2 O + 2 e X − ClO X 3 X − + 2 OH X − 2 0.36 base Fe Ferricyanide/ferrocyanide [ F e ( C N ) X 6 ] X 3 − + e X − ⇌ [ F e ( C N ) X 6 ] X 4 − \ce{[Fe(CN)6]^3- + e- <=> [Fe(CN)6]^4-} [ Fe ( CN ) X 6 ] X 3 − + e X − [ Fe ( CN ) X 6 ] X 4 − 1 0.358 — Ag Silver oxide/silver (button cell) A g X 2 O + H X 2 O + 2 e X − ⇌ 2 A g + 2 O H X − \ce{Ag2O + H2O + 2e- <=> 2Ag + 2OH-} Ag X 2 O + H X 2 O + 2 e X − 2 Ag + 2 OH X − 2 0.342 base Cu Copper(II)/copper C u X 2 + + 2 e X − ⇌ C u \ce{Cu^2+ + 2e- <=> Cu} Cu X 2 + + 2 e X − Cu 2 0.3419 — Cl Chlorate/chlorite (base) C l O X 3 X − + H X 2 O + 2 e X − ⇌ C l O X 2 X − + 2 O H X − \ce{ClO3- + H2O + 2e- <=> ClO2- + 2OH-} ClO X 3 X − + H X 2 O + 2 e X − ClO X 2 X − + 2 OH X − 2 0.33 base Hg Calomel/mercury (calomel electrode) H g X 2 C l X 2 + 2 e X − ⇌ 2 H g + 2 C l X − \ce{Hg2Cl2 + 2e- <=> 2Hg + 2Cl-} Hg X 2 Cl X 2 + 2 e X − 2 Hg + 2 Cl X − 2 0.26808 — Ag Silver chloride/silver (reference electrode) A g C l + e X − ⇌ A g + C l X − \ce{AgCl + e- <=> Ag + Cl-} AgCl + e X − Ag + Cl X − 1 0.22233 — S Sulfate/sulfurous acid S O X 4 X 2 − + 4 H X + + 2 e X − ⇌ H X 2 S O X 3 + H X 2 O \ce{SO4^2- + 4H+ + 2e- <=> H2SO3 + H2O} SO X 4 X 2 − + 4 H X + + 2 e X − H X 2 SO X 3 + H X 2 O 2 0.172 acid Cu Copper(II)/copper(I) C u X 2 + + e X − ⇌ C u X + \ce{Cu^2+ + e- <=> Cu+} Cu X 2 + + e X − Cu X + 1 0.153 — Sn Tin(IV)/tin(II) S n X 4 + + 2 e X − ⇌ S n X 2 + \ce{Sn^4+ + 2e- <=> Sn^2+} Sn X 4 + + 2 e X − Sn X 2 + 2 0.151 — S Sulfur/hydrogen sulfide S + 2 H X + + 2 e X − ⇌ H X 2 S \ce{S + 2H+ + 2e- <=> H2S} S + 2 H X + + 2 e X − H X 2 S 2 0.142 acid Co Hexaamminecobalt(III)/(II) [ C o ( N H X 3 ) X 6 ] X 3 + + e X − ⇌ [ C o ( N H X 3 ) X 6 ] X 2 + \ce{[Co(NH3)6]^3+ + e- <=> [Co(NH3)6]^2+} [ Co ( NH X 3 ) X 6 ] X 3 + + e X − [ Co ( NH X 3 ) X 6 ] X 2 + 1 0.108 — N Nitrogen/ammonia N X 2 + 6 H X + + 6 e X − ⇌ 2 N H X 3 \ce{N2 + 6H+ + 6e- <=> 2NH3} N X 2 + 6 H X + + 6 e X − 2 NH X 3 6 0.092 acid S Tetrathionate/thiosulfate S X 4 O X 6 X 2 − + 2 e X − ⇌ 2 S X 2 O X 3 X 2 − \ce{S4O6^2- + 2e- <=> 2S2O3^2-} S X 4 O X 6 X 2 − + 2 e X − 2 S X 2 O X 3 X 2 − 2 0.08 — Ag Silver bromide/silver A g B r + e X − ⇌ A g + B r X − \ce{AgBr + e- <=> Ag + Br-} AgBr + e X − Ag + Br X − 1 0.07133 — N Nitrate/nitrite (base) N O X 3 X − + H X 2 O + 2 e X − ⇌ N O X 2 X − + 2 O H X − \ce{NO3- + H2O + 2e- <=> NO2- + 2OH-} NO X 3 X − + H X 2 O + 2 e X − NO X 2 X − + 2 OH X − 2 0.01 base H Hydrogen ion/hydrogen (standard hydrogen electrode) 2 H X + + 2 e X − ⇌ H X 2 \ce{2H+ + 2e- <=> H2} 2 H X + + 2 e X − H X 2 2 0 acid Fe Iron(III)/iron F e X 3 + + 3 e X − ⇌ F e \ce{Fe^3+ + 3e- <=> Fe} Fe X 3 + + 3 e X − Fe 3 −0.037 — O Oxygen/hydroperoxide (base) O X 2 + H X 2 O + 2 e X − ⇌ H O X 2 X − + O H X − \ce{O2 + H2O + 2e- <=> HO2- + OH-} O X 2 + H X 2 O + 2 e X − HO X 2 X − + OH X − 2 −0.076 base Pb Lead(II)/lead P b X 2 + + 2 e X − ⇌ P b \ce{Pb^2+ + 2e- <=> Pb} Pb X 2 + + 2 e X − Pb 2 −0.1262 — Cr Chromate/chromium(III) hydroxide (base) C r O X 4 X 2 − + 4 H X 2 O + 3 e X − ⇌ C r ( O H ) X 3 + 5 O H X − \ce{CrO4^2- + 4H2O + 3e- <=> Cr(OH)3 + 5OH-} CrO X 4 X 2 − + 4 H X 2 O + 3 e X − Cr ( OH ) X 3 + 5 OH X − 3 −0.13 base Sn Tin(II)/tin S n X 2 + + 2 e X − ⇌ S n \ce{Sn^2+ + 2e- <=> Sn} Sn X 2 + + 2 e X − Sn 2 −0.1375 — Ag Silver iodide/silver A g I + e X − ⇌ A g + I X − \ce{AgI + e- <=> Ag + I-} AgI + e X − Ag + I X − 1 −0.15224 — Cu Copper(II) hydroxide/copper (base) C u ( O H ) X 2 + 2 e X − ⇌ C u + 2 O H X − \ce{Cu(OH)2 + 2e- <=> Cu + 2OH-} Cu ( OH ) X 2 + 2 e X − Cu + 2 OH X − 2 −0.222 base Ni Nickel(II)/nickel N i X 2 + + 2 e X − ⇌ N i \ce{Ni^2+ + 2e- <=> Ni} Ni X 2 + + 2 e X − Ni 2 −0.257 — Co Cobalt(II)/cobalt C o X 2 + + 2 e X − ⇌ C o \ce{Co^2+ + 2e- <=> Co} Co X 2 + + 2 e X − Co 2 −0.28 — Pb Lead sulfate/lead (lead–acid negative plate) P b S O X 4 + 2 e X − ⇌ P b + S O X 4 X 2 − \ce{PbSO4 + 2e- <=> Pb + SO4^2-} PbSO X 4 + 2 e X − Pb + SO X 4 X 2 − 2 −0.3588 — Cu Copper(I) oxide/copper (base) C u X 2 O + H X 2 O + 2 e X − ⇌ 2 C u + 2 O H X − \ce{Cu2O + H2O + 2e- <=> 2Cu + 2OH-} Cu X 2 O + H X 2 O + 2 e X − 2 Cu + 2 OH X − 2 −0.36 base Cd Cadmium(II)/cadmium C d X 2 + + 2 e X − ⇌ C d \ce{Cd^2+ + 2e- <=> Cd} Cd X 2 + + 2 e X − Cd 2 −0.403 — Cr Chromium(III)/chromium(II) C r X 3 + + e X − ⇌ C r X 2 + \ce{Cr^3+ + e- <=> Cr^2+} Cr X 3 + + e X − Cr X 2 + 1 −0.407 — Fe Iron(II)/iron F e X 2 + + 2 e X − ⇌ F e \ce{Fe^2+ + 2e- <=> Fe} Fe X 2 + + 2 e X − Fe 2 −0.447 — Fe Iron(III) hydroxide/iron(II) hydroxide (base) F e ( O H ) X 3 + e X − ⇌ F e ( O H ) X 2 + O H X − \ce{Fe(OH)3 + e- <=> Fe(OH)2 + OH-} Fe ( OH ) X 3 + e X − Fe ( OH ) X 2 + OH X − 1 −0.56 base Ni Nickel(II) hydroxide/nickel (base) N i ( O H ) X 2 + 2 e X − ⇌ N i + 2 O H X − \ce{Ni(OH)2 + 2e- <=> Ni + 2OH-} Ni ( OH ) X 2 + 2 e X − Ni + 2 OH X − 2 −0.72 base Cr Chromium(III)/chromium C r X 3 + + 3 e X − ⇌ C r \ce{Cr^3+ + 3e- <=> Cr} Cr X 3 + + 3 e X − Cr 3 −0.744 — Zn Zinc ion/zinc Z n X 2 + + 2 e X − ⇌ Z n \ce{Zn^2+ + 2e- <=> Zn} Zn X 2 + + 2 e X − Zn 2 −0.7618 — H Water/hydrogen (base) 2 H X 2 O + 2 e X − ⇌ H X 2 + 2 O H X − \ce{2H2O + 2e- <=> H2 + 2OH-} 2 H X 2 O + 2 e X − H X 2 + 2 OH X − 2 −0.8277 base Cr Chromium(II)/chromium C r X 2 + + 2 e X − ⇌ C r \ce{Cr^2+ + 2e- <=> Cr} Cr X 2 + + 2 e X − Cr 2 −0.913 — Mn Manganese(II)/manganese M n X 2 + + 2 e X − ⇌ M n \ce{Mn^2+ + 2e- <=> Mn} Mn X 2 + + 2 e X − Mn 2 −1.185 — Zn Zinc hydroxide/zinc (alkaline-cell anode) Z n ( O H ) X 2 + 2 e X − ⇌ Z n + 2 O H X − \ce{Zn(OH)2 + 2e- <=> Zn + 2OH-} Zn ( OH ) X 2 + 2 e X − Zn + 2 OH X − 2 −1.249 base Mn Manganese(II) hydroxide/manganese (base) M n ( O H ) X 2 + 2 e X − ⇌ M n + 2 O H X − \ce{Mn(OH)2 + 2e- <=> Mn + 2OH-} Mn ( OH ) X 2 + 2 e X − Mn + 2 OH X − 2 −1.56 base Ti Titanium(II)/titanium T i X 2 + + 2 e X − ⇌ T i \ce{Ti^2+ + 2e- <=> Ti} Ti X 2 + + 2 e X − Ti 2 −1.63 — Al Aluminium ion/aluminium A l X 3 + + 3 e X − ⇌ A l \ce{Al^3+ + 3e- <=> Al} Al X 3 + + 3 e X − Al 3 −1.662 — Mg Magnesium ion/magnesium M g X 2 + + 2 e X − ⇌ M g \ce{Mg^2+ + 2e- <=> Mg} Mg X 2 + + 2 e X − Mg 2 −2.372 — Na Sodium ion/sodium N a X + + e X − ⇌ N a \ce{Na+ + e- <=> Na} Na X + + e X − Na 1 −2.71 — Ca Calcium ion/calcium C a X 2 + + 2 e X − ⇌ C a \ce{Ca^2+ + 2e- <=> Ca} Ca X 2 + + 2 e X − Ca 2 −2.868 — Ba Barium ion/barium B a X 2 + + 2 e X − ⇌ B a \ce{Ba^2+ + 2e- <=> Ba} Ba X 2 + + 2 e X − Ba 2 −2.912 — K Potassium ion/potassium K X + + e X − ⇌ K \ce{K+ + e- <=> K} K X + + e X − K 1 −2.931 — Li Lithium ion/lithium L i X + + e X − ⇌ L i \ce{Li+ + e- <=> Li} Li X + + e X − Li 1 −3.0401 —