1. Reactions of Metals

2. Reactions of Metals with H2O
The metal is the anode and will be oxidized.
Mg  Mg e- E° = V
The water and substances in it will be the cathode.
Need to consider:
i) neutral water – WOA of the 3
2H2O e-  2OH H2 E° = V
ii) oxygenated water - requires a very long rxn time, or an accelerant, as O2 is not very water soluble
O H2O e-  4OH- E° = V
iii) acidic solution - as with acid rain
2H e-  H E° = V

3. Metals below the cathodic water ½ rxn will be spontaneous
That’s why:
Not all metals react with neutral water
eg. ones that will: ones that won’t:
Cr, Mn, V, Al, Ti, Be, Mg, Ce, Na, Ca, Ba, Cs, Ra, K, Li
Zn, Cr, Ga, Fe, Cd, Tl, Co, Ni,
Sn, Pb, Cu, Hg, Ag, Au
Not all metals react with oxygenated water
eg. ones that will: ones that won’t:
All the above, plus Cu, Fe, Pb, Sn, Ni, Co, Tl, Cd, Ga, Cr, Zn
Cu, Hg, Ag, Au
Not all metals react with acidic water
eg. ones that will: ones that won’t:
All the above except Cu
Cu, Hg, Ag, Au

4. Metals with Metals eg. Which metals will not protect Fe?
Alloys are created to change a metal’s properties
As most metals undergo oxidation – rust, corrosion, patina – other metals are added to stop the oxidation. eg. Fe or Cu need protection.
The protecting metal, called a sacrificial anode, is below on the table relative to the metal in question. It will undergo the oxidation and save the metal.
eg. Which metals will protect Fe?
All the metals below Fe in the Standard Reduction Table
eg. Which metals will not protect Fe?
All the metals above Fe in the Table

5. eg. a) Will Cr protect Fe? Determine the anode and determine the cell potential if the cathode is oxygenated water.
Cr  Cr e E° = V
SRA
Cr  Cr e E° = V
Fe  Fe e E° = V
Fe  Fe e E° = V 4 2x
an: Cr  Cr e E° = V 2 2
cat: O H2O e-  4OH- E° = V
2Cr + O H2O  2Cr OH- Ecell° = V
Ecell° is positive  spontaneous and Fe is protected

6. eg. b) Do the same for Ag and Fe.
Ag  Ag e- E° = V
Fe  Fe e- E° = V
SRA
Fe  Fe e- E° = V 4 2x
an: Fe  Fe e E° = V 2 2
cat: O H2O e-  4OH- E° = V
2Fe + O H2O  2Fe OH- Ecell° = V
 spontaneous and Fe is NOT protected