Oxidation and ReductionChapter 20

INTRO TO REDOXDay 1

A reaction in which electrons are transferred from one substance to another

Oxidation cannot occur without reduction Oxidation:

1. Losing of electrons

2. Increasing the oxidation charge (0 to +1 or -2 to -1) Reduction

1. Gaining of electrons

2. Reducing the oxidation charge (-1 to -2 or 1 to 0)

Definition

Number of charges the atom would have in a molecule if electrons were transferred completely

Rule #1Oxidation number of a free element is zero

Example: Mg, H2, Na, P4, S8, K

Rule #2 Oxidation number of an ion is the charge of the ion

Example: Mg2+, O2−, Al3+, Br−

Oxidation Numbers

Rule #3Oxidation number for H is +1 when bonded to a nonmetal

*Exception: when bonded to a metal it is −1Example: HCl, HF, LiH, H2O, NaH, MgH2

Rule #4 Oxygen’s oxidation number is −2

*Two Exceptions: peroxides and fluorine

Example: H2O2

OF2

1. HNO3

2. NO3−

3. MgCl2

4. CO32−

5. NH3

6. K3PO4

7. CaSO4

8. SiCl4

Practice

1. Give the oxidation # of the nitrogen atom:

2. Determine the oxidation # of the sulfur atom

3. Indicate the oxidation # of phosphorus in each:

Whiteboard Practice

a. N2

b. NO

c. N2O4

d. N2O5

e. NO2−

f. NH4+

a. H2S

b. S

c. H2SO4

d. S22−

e. HS−

f. SO2

a. HPO3

b. H3PO2

c. H3PO3

d. H3PO4

e. H4P2O7

f. H5P3O10

g. SO2

½ REACTIONSDay 2

2 Mg + O2 2 MgO

Redox Reaction

When an electron is lost (electrons appear as products) X0 X+1 + e−

Oxidation # goes up

Oxidation ½ Reaction

When an electron is gained (electrons appear as reactants) e− + Y+1 Y0

Oxidation # goes down

Reduction ½ Reaction

L E O goes G E R

Ways to RememberO I L R I G

OSE

LECTRONS

XIDATION

AIN

LECTRONS

EDUCTION

XIDATION

S OSING

EDUCTION

S AINING

Ex1 Na0 Na+1

Ex2 Fe+3 Fe+2

Ex3 N+1 N+2

Ex4 Mg+2 Mg0

Examples:

REDOX REACTIONSDay 3

HCl + Zn ZnCl2 + H2

Example 1:

Example 2:Mg + N2 Mg3N2

Example 3:

H2S + Cl2 HCl + S

Example 4:Fe + O2 Fe2O3

Assign oxidation numbers for each element. Then, for the following balanced redox reactions answer the following questions:

1) Fe(aq) + H2O2(aq) Fe+2(aq) + 2 OH-1(aq)

a. Write all the oxidation numbers (identify what changes)

b. Write the ½ reactions on the lines

_______________________ ________________________

(oxidation or reduction) (oxidation or reduction)c. Add the electrons to each ½ reaction

d. Identify each ½ reaction as oxidation or reduction

Classwork

2) Zn(s) + HCl(aq) H2(g) + ZnCl2(aq)

3) SbCl5 + 2 KI SbCl3 + I2 + 2 KCl