1. Redox Reactions

2. What is a redox reaction?
A Reduction reaction and an Oxidation reaction occurring simultaneously
Zn(s) + Cu2(aq)  Zn2+(aq) + Cu(s)

3. What is oxidation Loss of Electrons Gain of Oxygen Loss of Hydrogen
Zn(s)  Zn2+(aq)+ 2e–
Gain of Oxygen
Fe2O3 (s) + 3CO(g)  2Fe(s) + CO2 (g)
Loss of Hydrogen
2C8H18(s) + 25O2(g)  16CO2 (g) + 18H2O(l)
Gain in Oxidation Number

4. What is reduction Gain of Electrons Loss of Oxygen Gain of Hydrogen
Cu2(aq) + 2e–  Cu(s)
Loss of Oxygen
Fe2O3 (s) + 3CO(g)  2Fe(s) + CO2(g)
Gain of Hydrogen
2C8H18(s) + 25O2(g)  16CO2 (g) + 18H2O(l)
Loss in Oxidation Number

5. What is an oxidant or oxidising agent
They cause OXIDATION to occur
Undergo Reduction
Be reduced themselves

6. What is a reductant or reducing agent
They cause REDUCTON to occur
Undergo Oxidation
Are oxidized themselves

7. Oxidation Numbers    
Can use to determine if a reaction is a REDOX reaction
They have no physical meaning
They treat molecular substances as if they were ionic
Can also be referred to as Oxidation States 

8. Oxidation Number Rules
Oxid No. of the atoms of free (uncombined elements is zero
Cu in elemental copper is zero
O in elemental O2 is zero

9. Oxidation Number Rules
Oxid No of a monoatomic ion is the same as the charge on the ion
In CaCl2
Oxid No of Ca is 2+
Oxid No of Cl is 1–

10. Oxidation Number Rules
Oxid No of oxygen in most cases is –2
Eg CaO Ca = +2 , O = –2
Eg H2O H = +1, O = –2
Exception is H2O2 (peroxide) where Oxid No of O is –1

11. Oxidation Number Rules
Oxid No of Hydrogen in most cases is +1
Exception is in Metal Hydrides, where Oxid No = –1
Eg NaH where Na = +1, H = –1

12. Oxidation Number Rules
In a molecule or molecule ion the negative Oxid No. is assigned to the atom of the most electronegative element
Eg CF4 C = +4, F = –1
Flourine is the more electronegative so it has the negative Oxid No.

13. Oxidation Number Rules
The sum of the Oxid Nos in a molecule or neutral compound is zero
Eg H2O the sum is 2X(+1) + – 2 = 0

14. Oxidation Number Rules
The sum of the Oxid Nos in a molecule ion is equal to the charge on the ion
Eg NH4+ N = –3, H = +1
the sum is – 3 + 4(+1) = +1
For SO42– the Oxid No is –2

15. How Are Oxidation Numbers Used
An INCREASE in oxidation number indicates Oxidation
A DECREASE in oxidation number indicates Reduction
C(s) + O2(g)  CO2(g)  (–2)
C increases from 0 to Oxidation
O decreases from 0 to –2 Reduction

16. Writing Half Reactions
Balance all elements except hydrogen or oxygen
Balance the oxygen atoms by adding H2O
Balance the hydrogen atoms by adding H+ ions
Balance the charge on both sides by adding electrons e–
Add states