1. 10.1: Oxidization and Reduction Objectives S1

2. Essential Questions What is oxidation? Reduction?
How do you assign oxidation numbers?
What is a half reaction?
How do you write half reactions?

3. Oxidation and Reduction Reactions
Oxidation-Reduction reactions (redox) is when electrons are being gained and lost during a chemical reaction
Originally oxidation was defined as gain of oxygen while reduction was loss of oxygen

4. Oxidation and Reduction Reactions (cont)
Definitions using oxygen were limited in scope so following definition are now used:
Oxidation is loss of electrons
Reduction is gain of electrons
OIL RIG

5. Oxidation and Reduction Reactions (cont)
When magnesium and sulfur are heated together, they undergo an oxidation-reduction reaction to form magnesium sulfide. Applying Concepts Where did the electrons lost by magnesium go?

6. Oxidation Numbers
Oxidization numbers are how we keep track of what is happening to electrons
Similar to charge but not exactly the same
There are set rules when determining oxidation numbers

7. Oxidation # Rules Oxidation numbers are written per atom
Oxidation number of neutral element by itself is Zero
For most elements the oxidation # correlates with the charge of atom
For metals it will equal the metal’s charge
H is +1 when bonded to nonmetals and -1 when bonded to metals
Cl, Br, and I are -1 except when bonded to F and O
O is usually -2 unless bonded to F
F is always -1

8. Oxidation # Rules
Sum of oxidation # for all atoms in a compound is equal to 0
Sum of oxidation # equal the charge of the ion.
Figure out what you know and use the sum to find the rest.

9. Assigning Oxidation Numbers
Find the oxidation number for each element Na
CaO
N3-
SrCl2
NO3-
CoO
Cu(NO3)2
K2Cr2O7
Cs2(SO4)3

10. Half Reactions
Oxidation never occurs without reduction, they always occur in pairs
The total formula can be written in two parts
The oxidation half (where the oxidation number has increased)
The reduction half (where the oxidation number has decreased/reduced)

11. Writing Half Reactions
Cu + 2 AgNO3 → Cu(NO3)2 + 2 Ag
Step 1: Determine Oxidation numbers for each atom on each side of the equation
Step two: determine which two atoms have changed oxidation #s
Step three: Write half reactions for those two elements
Step four: Add electrons to balance charges or oxidation #
Recall: Oxidation is losing electrons and reduction is gaining electrons

12. Balancing Half-Reactions (cont)
Write balanced half reactions and identify the elements reduced and oxidized for the following:
TiO2 + 2 Mg → Ti + 2 MgO
Cl2 + 2 NaBr → 2 NaCl + Br2
5 CO + I2O5 → I2 + 5 CO2

13. Essential Questions What is oxidation? Reduction?
How do you assign oxidation numbers?
What is a half reaction?
How do you write half reactions?

14. 10.1 Tracked Assignment
worksheet