Chemical Reactions, Acids and Bases
Chemistry
6. Oxidation-Reduction (Redox) Reactions
Electrons are transferred from one atom to another.
Note that when one substance is oxidized, another compound must be reduced, and viceversa.
Oxidation = - electrons from a substance
Reduction = + electrons to a substance
Mg(s) + 2 HCl(aq)  MgCl2(aq) + H2(g)
0
+1 -1
+2 -1
0
•
•
•
Note: The transfer of electrons during oxidation-reduction reactions often produce
energy (when spontaneous), which can be in the form of electricity.
LEO the lion says GER (Loss of Electrons = Oxidation/Gain of Electrons = Reduction)
OIL RIG (oxidation is loss and reduction is gain)
Examples:
a)
Combustion: “rapid oxidation reaction in which a large amount of heat and
usually light are released”
C + O2  CO2, CO
S + O2  SO2
What was oxidized?
What was reduced?
b)
Metal + acid (SR): e.g.
Zn(s) + 2 HCl(aq)  ZnCl2(aq) + H2(g)
Total ionic equation:
What was oxidized?
What was reduced?
c)
Metal + salt (SR): e.g.
Mg(s) + CoSO4(aq)  MgSO4(aq) + Co(s)
Total ionic equation:
What was oxidized?
What was reduced?
Oxidation numbers help us keep track of what happens to the electrons in reactions.
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Chemical Reactions, Acids and Bases
Chemistry
Practice
Identify redox pairs and oxidation numbers.
Write net ionic equations for the following reactions.
2 Na(s) + SrBr2(aq)  Sr(s) + 2 NaBr(aq)
Zn(s) + H2SO3(aq)  ZnSO3(aq) + H2(g)
2 Na(s) + 2 H2O(l)  2 NaOH(aq) + H2(g)
Fe(s) + CuCl2(aq)  Cu(s) + FeCl2(aq)
Predicting Products of Different Reaction Types
Class of reaction
Synthesis
Decomposition
Reactants
two or more substances
one compound
Single Replacement
a metal and a compound
Double Replacement
a nonmetal (halogen) and a
compound
two compounds dissolved in
water
hydrocarbon + oxygen
Combustion
(restricted definition)
Oxidation-Reduction
one or more substances
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Probable Products