Definition
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If oxidation occurs, then reduction must
also occur
Any chemical process in which elements
undergo a change in oxidation number is a
Redox reaction
Example
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2Na + Cl2 → 2Na+ + 2ClThis reaction can be thought of as two half
reactions
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2 Na → 2Na+ + 2e
Cl2 + 2e → 2Cl-
oxidation
reduction
These two reactions together are called a
redox reaction
Identifying Redox
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SO2 + H2O + O2 → H2SO4
NaCl + Ag(NO3) → Na(NO3) + AgCl
Practice
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Determine if each below is a redox reaction
SO3 + H2O → H2SO4
2KNO3 → 2KNO2 + O2
H2 + CuO → Cu + H2O
More Definitions
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Reducing Agents – elements that undergo
oxidation (the cause reduction in another
element)
Oxidizing Agents – undergo reduction
Mg + Cu(NO3) → Cu + Mg(NO3)
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Mg is reducing agent – being oxidized
Cu2+ is oxidizing agent – being reduced
Corrosion
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When a metal is reduced
When two metals are in contact, the one
that is the better reducing agent (most
active) will give up electrons to the other
one
The metal that receives the electrons is
reduced – called corrosion
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When zinc is wrapped around the Fe nail,
Zn is oxidized, so Fe corrodes
When copper is wrapped around the Fe
nail, Fe is oxidized, so Cu corrodes