1. Unit 6 Oxidation/Reduction and Electrochemistry
November 28, 2014

2. Redox Chemistry
Redox (reduction/oxidation) chemistry deals with chemical reactions in terms of electron transfer.
The terminology comes from the reactions metals undergo.

3. Reduction Reactions:
Reduction reactions were originally associated with a loss of mass in metal ores upon heating or reacting with carbon:
Reduction of tin (IV) oxide to tin metal: Δ
SnO2 (s) C (s) Sn(s) + CO2 (g)
150.7 g/mol g/mol

4. Oxidation Reactions:
Oxidation reactions were originally associated with the reaction of metals with oxygen:
Oxidation of tin metal to tin (IV) oxide:
Sn (s) O2 (g) SnO2 (s)

5. Redox Reactions and Electrons
In simplest form, a redox reaction involves the transfer of electrons:
Charge:
SnO C Sn + CO2
In this reaction, the Sn4+ ion has gained four electrons to be reduced in to Sn metal.

6. Redox Reactions and Electrons
Charge:
Sn O2 SnO2
In this reaction, tin metal has lost four electrons to be oxidized.
Note that oxygen has therefore gained four electrons itself to be reduced.
4 e-

7. Oxidation-Reduction Reactions
Cu Mg Mg2+ + Cu
The substance that loses electrons is said to be oxidized.
The substance that gains electrons is said to be reduced.
2 e-
 Mg is oxidized
 Cu2+ is reduced

8. LEO the lion says…
GER!!!

9. Lose Gain Electrons says Electrons Oxidation Reduction

10. Other Confusing Redox Language:
Cu Mg Mg2+ + Cu
reduced oxidized
A substance that oxidizes another is called an oxidizing agent.
A substance that reduced another is called a reducing agent.
 Cu2+ is the oxidizing agent.
 Mg is the reducing agent.

11. Oxidation Number
Oxidation number is the actual or assumed charge of an atom in a molecule or of an ion.
Assigning oxidation numbers is very similar to assigning valences for elements in compounds from Grade 11 Chemistry.

12. Determining Oxidation Number:
1. Assume the most electronegative element has a full share of electrons pairs involved in any bond (ionic or covalent). 2. Use the trends in the periodic table to help determine oxidation number. 3. Deduce other oxidation numbers from other oxidation numbers of elements in the compound or ion.

13. Common Oxidation Numbers:
Atom or Ion
Oxidation Number
Examples
all atoms in elemental form.
Na (s); Cl2
hydrogen in all compounds. +1
H in HCl
→ except in hydrides -1
H in LiH

14. Atom or Ion
Oxidation Number
Examples
oxygen in all compounds -2
O in CO2
→ except in peroxides -1
O in H2O2
all monatomic ions
charge on the ion
Fe2+ is +2; Br- is –1