oxidation- reduction reaction review. oxidation-reduction (“redox”) reactions most common...
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Oxidation-Reduction Reaction Review
Oxidation-Reduction (“Redox”) Reactions
• Most common reaction • Process often written as two “half-reactions”—separating the
oxidation and reduction
• Deals with electron transfer between ionic compounds
• One compound wants to GIVE electrons, other compound wants to TAKE electrons.
• Identified by a change in oxidation number
2 chemical processes happening at the same time ! 1) Reduction—
• GAIN of electrons in element• Compound becomes more NEGATIVE• DECREASE in oxidation number
2) Oxidation• LOSS of electrons • Compound becomes more POSITIVE • INCREASE in oxidation number
•Oxidation and Reduction MUST happen together—can’t have one without the other.
•electrons gained = electrons lost
Example 1:
•2Na + Cl2 2Na+ Cl-
Practice• Which equations are reduction half-reactions and which
are oxidation half-reactions.
1)Zn+2 + 2e- Zn
2)Ag Ag+ + e-
3)Cu+2 + 2e- Cu
4)Al Al+3 + 3e-
Oxidation Numbers/State
• Allows us to identify redox reactions
• A change in these numbers------ REDOX REACTION ! ! !
• Acts like all chemical compounds are ionic----gives atom a charge it would have IF it was ionic
Rule # 1 Examples
• Br2
• MgCl2• C6H12O6
• Cu• Ag• Fe
Oxidation Number Rules
2) Sum of oxidation numbers for an ion = ion’s charge
Examples:
•SO4-2
•NH4+
•Al ion •Cl ion
Oxidation Number Rules
3) Group 1A metals = +1
Group 2A metals = +2
Examples: MgSO4
K3PO4
Oxidation Number Rules
4) For the majority of chemical compounds—• F = -1• H = +1 (sometimes will have -1) • O = -2
Examples: NH3
H2O
CO
HF
KF
Oxidation Number Rules
5) Group 7A Elements = -1
Group 6A Elements = -2
Group 5A Elements = -3
**When combined with a metal in a binary compound !
Rule #5 Examples
• CaF2
• Li2S
• Mg3N
• K3P
Let’s Practice !
• Calculate the oxidation number of chromium in each
1)CrO4-2
2)Cr2O7-2
3)CrO2
More Practice! • State which reactions are oxidation-reduction reactions.
State which compound is being oxidized and which compound is being reduced.
1)Cu + 2Ag+ Cu+2 + 2Ag
2)CH3CO2H + OH- CH3CO2- + H2O
3)SF4 + F2 SF6
4)CuSO4 + BaCl2 BaSO4 + CuCl2
Homework
Read pp. 755-758
Oxidation-Reduction Review Sheet