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Electrode Potential Values
The values of electrode potential provide information on:
 The strength of metals as reducing agents (high negative E o values)
 The strength of non-metals as oxidising agents (high positive Eo values)
 The prediction of the spontaneity of redox reactions. If the overall value of E o for a
cell is positive, the reaction will occur spontaneously.
 Calculating the EMF or voltage of electrochemical (galvanic cells)
Reducing Agents and Eo values
Electrode potentials involving metals indicate:
 How readily hydrated metal ions in solution gain electrons (are reduced) to form
metal ions. The more positive the Eo value, the more likely it is that the metal ion
will form the metal.
 How readily metal atoms release electrons (are oxidised) to produce hydrated
ions in solution. The most reactive metals (those that are the best reductants), are
those that have the most negative electrode reduction potential values.
Arranging the metals in order of their electrode potential (Eo) values produces the
electrochemical series. Electrode potentials are good indicators of metal
reactivities. The two exceptions are lithium and calcium, which are chemically less
reactive than their Eo values would indicate.
Electrochemical
series
Lithium
Li
Potassium K
Calcium
Ca
Sodium
Na
Magnesium Mg
Aluminium Al
Zinc
Zn
Iron
Fe
Lead
Pb
Copper
Cu
Silver
Ag
Gold
Au
Metal ion/atom
half-equation
Li+ + e  Li
K+ + e  K
Ca2++ 2e  Ca
Na+ + e  Na
Mg2+ + 2e  Mg
Al3+ + 3e  Al
Zn2+ + 2e  Zn
Fe2+ + 2e  Fe
Pb2+ + 2e  Pb
Cu2+ 2e  Cu
Ag+ + e  Ag
Au+ + e  Au
Electrode potential
Eo / V
-3.02
-2.92
-2.87
-2.71
-2.30
-1.66
-0.76
-0.47
-0.13
+0.34
+0.81
+1.50
Metals with negative Eo values can reduce aqueous hydrogen ions to hydrogen gas.
If the electrode potential is positive, the metal atoms do not reduce hydrogen ions
and so they do not react with acids.
Oxidising Agents and Eo values