Transcript notes

Lecture 5
Reduction-Oxidation Reactions
Redox
What is a redox reaction?
 ==> When in the reaction, electrons are
being transferred from one substance to
another.
 What has to happen? Something has to be
gaining e- (becoming negative) and
something has to be losing e- (becoming
positive).
How do you tell?
Need to assign each individual element an oxidation number.
 Rules:
1) When atoms are by themselves (including diatomics) they have an
oxidation # of 0. Ex: Na, N2, Cl2, O2, Fe, Mg
How do you tell?
Need to assign each individual element an oxidation number.

Rules:
1)
2)
When atoms are by themselves (including diatomics) they have
an oxidation # of 0.
Monatomic ions have an oxidation # equaling their charge.
Ex: Cl-1, Na+1, N-3, O-2, Fe+3, Mg+2
How do you tell?
Need to assign each individual element an oxidation number.

Rules:
1)
2)
When atoms are by themselves (including diatomics) they have
an oxidation # of 0.
Monatomic ions have an oxidation # equaling their charge.
3)
Compounds are neutral. Sum of oxidation # must be 0
How do you tell?
Need to assign each individual element an oxidation number.

Rules:
1)
2)
When atoms are by themselves (including diatomics) they have
an oxidation # of 0.
Monatomic ions have an oxidation # equaling their charge.
3)
Compounds are neutral. Sum of oxidation # must be 0
4)
Polyatomic ions must have the sum of oxidation # equal their
charge.
How do you tell?
Need to assign each individual element an oxidation number.

Rules:
5) Oxygen in a compound usually has a charge of -2.
Exception: peroxide where it equals -1
How do you tell?
Need to assign each individual element an oxidation number.

Rules:
5) Oxygen in a compound usually has a charge of -2.
Exception: peroxide where it equals -1
6) In covalent compounds, hydrogen is +1.
How do you tell?
Need to assign each individual element an oxidation number.

Rules:
5) Oxygen in a compound usually has a charge of -2.
Exception: peroxide where it equals -1
6) In covalent compounds, hydrogen is +1.
Application: NO2
NO
NO3l-
HC2H3O2
SO4-2
How do you tell?
Need to assign each individual element an oxidation number.

Rules:
5) Oxygen in a compound usually has a charge of -2.
Exception: peroxide where it equals -1
6) In covalent compounds, hydrogen is +1.
7) If else fails use the periodic table.
Group 1 = 1+
Group 2 = 2+
Group 7 = 1-
More Practice
 Try these brain busters!




KMnO4
H2CO3
PH3
MgC4H4O6
Remember!
 Oxidation can be all sorts of numbers, even
fractions :]
Fe304
Oxygen is -2, so what does Fe have to be?
Remember!
 Oxidation can be all sorts of numbers even
fractions :]
Fe304
Oxygen is -2 so what does Fe have to be?
Iron is + 8/3
Characteristics of Redox reactions:
 1) Oxidation-substance losing electrons
Characteristics of Redox reactions:
 1) Oxidation-substance losing electrons
 2) Reduction-substance gaining electrons
Characteristics of Redox reactions:
 1) Oxidation-substance losing electrons
 2) Reduction-substance gaining electrons
Lots of Ways to Remember!
 Oil Rig
O I L
R I G
Lots of Ways to Remember!
 Leo goes Ger
L E O
goes
G E R
Lots of Ways to Remember!
 Olé!
O
L E !
2 Na(s) + Cl2(g) ==> 2NaCl(s)
 What’s being oxidized? Reduced?
0
0
1+ 12 Na(s) + Cl2(g) ==> 2NaCl(s)
 What’s being oxidized? Reduced?
Oxidized: Na
Reduced: Cl2