oxidation and reduction chapter 20 intro to redox day 1
TRANSCRIPT
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