Metal Samples MS2500L, Operator'S Manual

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42
Oxidation Reduction Potentials
The table below is a listing of some useful oxidation-reduction potentials. These values represent the
thermodynamic tendency for the indicated reaction to occur on a relative basis. All potential values are
compared to an arbitrary value of 0.00 volts which is assigned to the hydrogen oxidation reaction. The
more negative a value, the more likely the reaction will proceed in the direction shown in table. Thus we
see that zinc oxidation
Zn Zn
++
+ 2e- E = -0.763 volts
is more likely to occur than iron oxidation
Fe Fe
++
+ 2e- E = -0.44 volts
which, in turn, is more likely than hydrogen oxidation
H
2
2H
+
+ 2e- E = 0.00 volts
Some other generalizations drawn from the standard oxidation reduction potential table are:
1. Oxygen is a stronger oxidizing agent than hydrogen ion.
2. Iron is more reactive than lead, copper or silver.
3. Gold is very unreactive.
More Reactive Reaction Eo (volts)
Na Na
+
+ e- - 2.71
Mg Mg
++
+ 2e- - 2.38
Al Al
+++
+ 3e- - 1.66
Zn Zn
++
+ 2e- - 0.763
Fe Fe
++
+ 2e- - 0.409
Ni Ni
++
+ 2e- - 0.250
Pb Pb
++
+ 2e- - 0.126
H 2H
+
+ 2e- 0.00 Reference
Cu Cu
++
+ 2e- + 0.34
4OH O
2
+ 2H
2
O + 4e- + 0.401
Fe
+2
Fe
+++
+ e- + 0.771
Ag = Ag
+
+ e- + 0.799
2H Hg
2
++
+ 2e- + 0.905
2Br- Br
2
+ 2e- + 1.06
2H
2
O O
2
+ 4H
+
+ 4e- + 1.23
2Cl- Cl
2
+ 2e- + 1.36
Pt Pt
++
+ 2e- + 1.2
Au Au
+++
+ 3e- + 1.498
More Noble