Fe mechanisms

Mechanism #1 (pH 2)

Anode:

2Fe ( s ) 4e 2Fe ( aq ) 2 + ( E ° = + 0.4 47V ) (1)

2H 2 O ( l ) 4e O 2 ( g ) + 4H ( aq ) + ( E ° = 1 . 229V ) (2)

Solution:

2Fe ( aq ) 2 + + 4OH ( aq ) 2 Fe ( OH ) 2 ( s ) (3)

Cathode:

8H ( aq ) + + 8e 4H 2 ( g ) ( E ° = 0.000 V ) (4)

Total:

2Fe ( s ) + 6H 2 O ( l ) O 2 ( g ) + 4H 2 ( g ) + 2Fe ( OH ) 2 ( s ) (5)

Mechanism #2 (pH 7)

Anode:

2Fe ( s ) 4e 2Fe ( aq ) 2 + ( E ° = + 0.4 47V ) (1)

Fe ( aq ) 2 + e Fe ( aq ) 3 + ( E ° = 0.771 V ) (6)

Fe ( s ) 3e Fe ( aq ) 3 + ( E ° = + 0.03 7V ) (7)

Solution:

Fe ( aq ) 2 + + 2OH ( aq ) Fe ( OH ) 2 ( s ) (3)

2Fe ( aq ) 3 + + 6OH ( aq ) 2Fe ( OH ) 3 ( s ) (8)

Cathode:

8H 2 O ( l ) + 8e 4H 2 ( g ) + 8OH ( aq ) ( E ° = 0. 828V ) (9)

Total:

3Fe ( s ) + 8H 2 O ( l ) Fe ( OH ) 2 ( s ) + 2Fe ( OH ) 3 ( s ) + 4H 2 ( g ) (10)

Mechanism #3 (pH 12)

Anode:

2Fe ( s ) 6e 2Fe ( aq ) 3 + ( E ° = + 0.03 7V ) (7)

Solution:

2Fe ( aq ) 3 + + 6OH ( aq ) 2Fe ( OH ) 3 ( s ) (8)

Cathode:

6H 2 O ( l ) + 6e 3H 2 ( g ) + 6OH ( aq ) ( E ° = 0.82 8V ) (9)

Total:

2Fe ( s ) + 6H 2 O ( l ) 2Fe ( OH ) 3 ( s ) + 3H 2 ( g ) (11)

Al mechanism

Mechanism (pH 7)

Anode:

Al ( s ) 3e Al ( aq ) 3 + ( E ° = + 1.66 V ) (12)

2H 2 O ( l ) 4e O 2 ( g ) + 4H ( aq ) + ( E ° = 1.22 9V ) (2)

Solution:

Al ( aq ) 3 + + 3OH ( aq ) Al ( OH ) 3 ( s ) (12)

Al ( OH ) 4 ( aq ) OH ( aq ) + Al ( OH ) 3 ( s ) (13)

Cathode:

4H 2 O ( l ) + 4e 2H 2 ( g ) + 4OH ( aq ) ( E ° = 0. 828V ) (9)

Al ( s ) + 4OH ( aq ) 3e Al ( OH ) 4 ( aq ) (14)

Total:

2Al ( s ) + 8H 2 O ( l ) 5H 2 ( g ) + 2Al ( OH ) 3 ( s ) + O 2 ( g ) (15)