Cặp oxy hóa khử Fe3+ /Fe2+ có thế điện cực theo phương trình Nernst là:

\[{\varepsilon _{F{e^{3 + }}/F{e^{2 + }}}} = {\varepsilon ^0}_{F{e^{3 + }}/F{e^{2 + }}} - \frac{{RT}}{{2F}}\lg \frac{{\left[ {F{e^{2 + }}} \right]}}{{\left[ {F{e^{3 + }}} \right]}}\]

\[{\varepsilon _{F{e^{3 + }}/F{e^{2 + }}}} = {\varepsilon ^0}_{F{e^{3 + }}/F{e^{2 + }}} - \frac{{RT}}{F}\lg \frac{{\left[ {F{e^{2 + }}} \right]}}{{\left[ {F{e^{3 + }}} \right]}}\]

\[{\varepsilon _{F{e^{3 + }}/F{e^{2 + }}}} = {\varepsilon ^0}_{F{e^{3 + }}/F{e^{2 + }}} + \frac{{RT}}{F}\lg \frac{{\left[ {F{e^{2 + }}} \right]}}{{\left[ {F{e^{3 + }}} \right]}}\]

\[{\varepsilon _{F{e^{3 + }}/F{e^{2 + }}}} = {\varepsilon ^0}_{F{e^{3 + }}/F{e^{2 + }}} + \frac{{RT}}{F}\lg \frac{{\left[ {F{e^{2 + }}} \right]}}{{\left[ {F{e^{3 + }}} \right]}}\]