Fe Mechanisms

Medium

Reaction

Mechanism # 1 (pH 2)

Anode

${\text{2Fe}}_{\left(\text{s}\right)}-{\text{4e}}^{-}\to {\text{2Fe}}_{\left(\text{aq}\right)}^{\text{2}+}$ (E˚ = +0.447 V) (1)

${\text{2H}}_{\text{2}}{\text{O}}_{\left(\text{l}\right)}-{\text{4e}}^{-}\to {\text{O}}_{\text{2}\left(\text{g}\right)}+{\text{4H}}_{\left(\text{aq}\right)}^{+}$ (E˚ = −1.229 V) (2)

Solution

${\text{2Fe}}_{\left(\text{aq}\right)}^{\text{2}+}+{\text{4OH}}_{\left(\text{aq}\right)}^{-}\to \text{2Fe}{\left(\text{OH}\right)}_{\text{2}\left(\text{s}\right)}$ (3)

Cathode

${\text{8H}}_{\left(\text{aq}\right)}^{+}+{\text{8e}}^{-}\to {\text{4H}}_{\text{2}\left(\text{g}\right)}$ (E˚ = 0.000 V) (4)

Total

${\text{2Fe}}_{\left(\text{s}\right)}+{\text{6H}}_{\text{2}}{\text{O}}_{\left(\text{l}\right)}\to {\text{O}}_{\text{2}\left(\text{g}\right)}+{\text{4H}}_{\text{2}\left(\text{g}\right)}+\text{2Fe}{\left(\text{OH}\right)}_{\text{2}\left(\text{s}\right)}$ (5)

Mechanism # 2

(pH 7)

Anode

${\text{2Fe}}_{\left(\text{s}\right)}-{\text{4e}}^{-}\to {\text{2Fe}}_{\left(\text{aq}\right)}^{\text{2}+}$ (E˚ = +0.447 V) (1)

${\text{Fe}}_{\left(\text{aq}\right)}^{\text{2}+}-{\text{e}}^{-}\to {\text{Fe}}_{\left(\text{aq}\right)}^{3+}$ (E˚ = −0.771 V) (6)

${\text{Fe}}_{\left(\text{s}\right)}-{\text{3e}}^{-}\to {\text{Fe}}_{\left(\text{aq}\right)}^{3+}$ (E˚ = +0.037 V) (7)

Solution

${\text{2Fe}}_{\left(\text{aq}\right)}^{\text{2}+}+{\text{4OH}}_{\left(\text{aq}\right)}^{-}\to \text{2Fe}{\left(\text{OH}\right)}_{\text{2}\left(\text{s}\right)}$ (3)

${\text{2Fe}}_{\left(\text{aq}\right)}^{3+}+{\text{6OH}}_{\left(\text{aq}\right)}^{-}\to \text{2Fe}{\left(\text{OH}\right)}_{\text{3}\left(\text{s}\right)}$ (8)

Cathode

${\text{8H}}_{\text{2}}{\text{O}}_{\left(\text{l}\right)}+{\text{8e}}^{-}\to {\text{4H}}_{\text{2}\left(\text{g}\right)}+{\text{8OH}}_{\left(\text{aq}\right)}^{-}$ (E˚ = −0.828 V) (9)

Total

${\text{3Fe}}_{\left(\text{s}\right)}+{\text{8H}}_{\text{2}}{\text{O}}_{\left(\text{l}\right)}\to \text{Fe}{\left(\text{OH}\right)}_{\text{2}\left(\text{s}\right)}+\text{2Fe}{\left(\text{OH}\right)}_{\text{3}\left(\text{s}\right)}+{\text{4H}}_{\text{2}\left(\text{g}\right)}$ (10)

Mechanism # 3

(pH 12)

Anode

${\text{Fe}}_{\left(\text{s}\right)}-{\text{3e}}^{-}\to {\text{Fe}}_{\left(\text{aq}\right)}^{3+}$ (E˚ = +0.037 V) (7)

Solution

${\text{2Fe}}_{\left(\text{aq}\right)}^{3+}+{\text{6OH}}_{\left(\text{aq}\right)}^{-}\to \text{2Fe}{\left(\text{OH}\right)}_{\text{3}\left(\text{s}\right)}$ (8)

Cathode

${\text{8H}}_{\text{2}}{\text{O}}_{\left(\text{l}\right)}+{\text{8e}}^{-}\to {\text{4H}}_{\text{2}\left(\text{g}\right)}+{\text{8OH}}_{\left(\text{aq}\right)}^{-}$ (E˚ = -0.828 V) (9)

Total

${\text{2Fe}}_{\left(\text{s}\right)}+{\text{6H}}_{\text{2}}{\text{O}}_{\left(\text{l}\right)}\to \text{2Fe}{\left(\text{OH}\right)}_{\text{3}\left(\text{s}\right)}+{\text{3H}}_{\text{2}\left(\text{g}\right)}$ (11)

Al Mechanism

(pH 7)

Anode

${\text{Al}}_{\left(\text{s}\right)}-{\text{3e}}^{-}\to {\text{Al}}_{\left(\text{aq}\right)}^{3+}$ (E˚ = +1.660 V) (12)

${\text{2H}}_{\text{2}}{\text{O}}_{\left(\text{l}\right)}-{\text{4e}}^{-}\to {\text{O}}_{\text{2}\left(\text{g}\right)}+{\text{4H}}_{\left(\text{aq}\right)}^{+}$ (E˚ = −1.229 V) (2)

Solution

${\text{Al}}_{\left(\text{aq}\right)}^{3+}+{\text{3OH}}_{\left(\text{aq}\right)}^{-}\to \text{Al}{\left(\text{OH}\right)}_{\text{3}\left(\text{s}\right)}$ (13)

$\text{Al}{\left(\text{OH}\right)}_{4\left(\text{aq}\right)}^{-}\to {\text{OH}}_{\left(\text{aq}\right)}^{-}+\text{Al}{\left(\text{OH}\right)}_{\text{3}\left(\text{s}\right)}$ (14)

Cathode

${\text{8H}}_{\text{2}}{\text{O}}_{\left(\text{l}\right)}+{\text{8e}}^{-}\to {\text{4H}}_{\text{2}\left(\text{g}\right)}+{\text{8OH}}_{\left(\text{aq}\right)}^{-}$ (E˚ = −0.828 V) (9)

Total

${\text{Al}}_{\left(\text{s}\right)}+{\text{5H}}_{\text{2}}\text{O}\to {\text{O}}_{\text{2}\left(\text{g}\right)}+\left(7/2\right){\text{H}}_{\text{2}\left(\text{g}\right)}+\text{Al}{\left(\text{OH}\right)}_{\text{3}\left(\text{s}\right)}$ (15)