Oxidation-Reduction (Redox) Reactions
Oxidation-Reduction ReactionsElectron transfer between ionic compounds, change in oxidation
numbers
One compound wants to GIVE electrons, other compound wants to TAKE electrons.
Reduction— GAIN of electrons in element/compound Compound becomes more NEGATIVE DECREASE in oxidation number
Oxidation LOSS of electrons in element/compound Compound becomes more POSITIVE INCREASE in oxidation number
Oxidation CANNOT happen without Reduction.
Reduction CANNOT happen without Oxidation
Both have to happen in a redox reaction ! ! !
Example 1:Mg (s) + Cu+2 (aq) Mg+2
(aq) + Cu (s)
Ex. 2: 2Mg + O2 2MgOWhere does reduction happen?Which does oxidation happen?
Example 3:
2 Na + Cl2 2NaCl
Assign oxidation numbersIdentify where oxidation occurs, where reduction occurs.
Determine whether each of these reactions is a oxidation-reduction reaction. If so, identify what is oxidized and what is reduced.
1) Mg + 2HCl MgCl2 + H2
2) I2 + 3Cl2 2 ICl3
3) NaOH + HCl NaCl + H2O
4) 2Na + 2H2O 2NaOH + H2
Half-Reaction Describes the oxidation or reduction process going on in a
redox reaction
2 half-reactions make ONE redox reaction
Contains “half” of a redox reaction
Half-Reactions
A method of separating the OXIDATION part of a chemical reaction from the REDUCTION part.
Oxidation process---one equationReduction process---one equation
Then we put it all together.
Half-Reaction Example Cu+2
(aq) + 2e-1 Cu (s) Reduction
Mg (s) Mg+2 (aq) + 2e-1 Oxidation
Total: Mg(s) + Cu+2(aq) Mg+2
(aq) + Cu(s)
Example 4: Oxidation: Cu (s) Cu+2
(aq) + 2e -1 Reduction: Ag+1
(aq) + 1e -1 Ag (s)
*When electrons do not balance, multiply one or both half-reactions when needed to balance the amount of electrons gained and lost in the reaction. **
How do we write half-reactions? Original Equation: 2 Na + Cl2 2NaCl
Oxidation Half-Reaction: 2Na 2Na+ + 2e-
Show electrons “lost” through process, 2 because you have 2 Na
Reduction Half-Reaction:Cl2 + 2e- 2Cl- Show electrons “gained” through process, 2 because you
have 2 Cl**Electrons MUST equal in number for BOTH half-reactions!!!
Putting Redox Equation back together……Original Equation:
2 Na + Cl2 2NaClAssign Oxidation Numbers Identify where oxidation/reduction happening
Half-Reactions:Oxidation: 2Na 2Na+ + 2e-
Reduction: Cl2 + 2e- 2Cl- Cancel elements and electrons existing on both sides, Add half-reactions together.
RESULT ! !2 Na + Cl2 2NaCl
Example 5: 2Mg + O2 2MgO
Example 6: Cu(s) + NO3 Cu+2 + NO
Example 7: Zn + 2HCl ZnCl2 + H2
Practice!
Write half-reactions and balance if the reaction is redox !
1) Mg + 2HCl MgCl2 + H2
2) I2 + 3Cl2 2 ICl33) NaOH + HCl NaCl + H2O4) 2Na + 2H2O 2NaOH + H2