Fe mechanisms

Mechanism #1 (pH 2)

Anode:

${\text{2Fe}}_{\left(\text{s}\right)}-{\text{4e}}^{-}\to {\text{2Fe}}_{\left(\text{aq}\right)}^{2+}\left(E°=+0.4\text{47V}\right)$ (1)

${\text{2H}}_{\text{2}}{\text{O}}_{\left(\text{l}\right)}-{\text{4e}}^{-}\to {\text{O}}_{\text{2}\left(\text{g}\right)}+{\text{4H}}_{\left(\text{aq}\right)}^{+}\left(E°=-\text{1}.\text{229V}\right)$ (2)

Solution:

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

Cathode:

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

Total:

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

Mechanism #2 (pH 7)

Anode:

${\text{2Fe}}_{\left(\text{s}\right)}-{\text{4e}}^{-}\to {\text{2Fe}}_{\left(\text{aq}\right)}^{2+}\left(E°=+0.4\text{47V}\right)$ (1)

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

${\text{Fe}}_{\left(\text{s}\right)}-{\text{3e}}^{-}\to {\text{Fe}}_{\left(\text{aq}\right)}^{3+}\left(E°=+0.03\text{7V}\right)$ (7)

Solution:

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

${\text{8H}}_{\text{2}}{\text{O}}_{\left(\text{l}\right)}+{\text{8e}}^{-}\to {\text{4H}}_{\text{2}\left(\text{g}\right)}+{\text{8OH}}_{\left(\text{aq}\right)}^{-}\left(E°=-0.\text{828V}\right)$ (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:

${\text{2Fe}}_{\left(\text{s}\right)}-{\text{6e}}^{-}\to {\text{2Fe}}_{\left(\text{aq}\right)}^{3+}\left(E°=+0.03\text{7V}\right)$ (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:

${\text{6H}}_{\text{2}}{\text{O}}_{\left(\text{l}\right)}+{\text{6e}}^{-}\to {\text{3H}}_{\text{2}\left(\text{g}\right)}+{\text{6OH}}_{\left(\text{aq}\right)}^{-}\left(E°=-0.82\text{8V}\right)$ (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

Mechanism (pH 7)

Anode:

${\text{Al}}_{\left(\text{s}\right)}-{\text{3e}}^{-}\to {\text{Al}}_{\left(\text{aq}\right)}^{3+}\left(E°=+1.66\text{V}\right)$ (12)

${\text{2H}}_{\text{2}}{\text{O}}_{\left(\text{l}\right)}-{\text{4e}}^{-}\to {\text{O}}_{\text{2}\left(\text{g}\right)}+{\text{4H}}_{\left(\text{aq}\right)}^{+}\left(E°=-1.22\text{9V}\right)$ (2)

Solution:

${\text{Al}}_{\left(\text{aq}\right)}^{3+}+{\text{3OH}}_{\left(\text{aq}\right)}^{-}\to \text{Al}{\left(\text{OH}\right)}_{\text{3}\left(\text{s}\right)}$ (12)

$\text{Al}{\left(\text{OH}\right)}_{4\left(\text{aq}\right)}^{-}\to {\text{OH}}_{\left(\text{aq}\right)}^{-}+\text{Al}{\left(\text{OH}\right)}_{\text{3}\left(\text{s}\right)}$ (13)

Cathode:

${\text{4H}}_{\text{2}}{\text{O}}_{\left(\text{l}\right)}+{\text{4e}}^{-}\to {\text{2H}}_{\text{2}\left(\text{g}\right)}+{\text{4OH}}_{\left(\text{aq}\right)}^{-}\left(E°=-0.\text{828V}\right)$ (9)

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

Total:

${\text{2Al}}_{\left(\text{s}\right)}+{\text{8H}}_{\text{2}}{\text{O}}_{\left(\text{l}\right)}\to {\text{5H}}_{\text{2}\left(\text{g}\right)}+\text{2Al}{\left(\text{OH}\right)}_{\text{3}\left(\text{s}\right)}+{\text{O}}_{\text{2}\left(\text{g}\right)}$ (15)