Transcript Monday 3/19/2012 E-Day

UNIT 10: REDOX
How can we assign oxidation numbers?
How can we recognize a RedOx reaction?
How can we identify which species is oxidized/reduced?
How can we write half reactions?
How can we balance equations using the half reaction method?
How can we balance RedOx reactions in acidic and basic solutions?
What are free radicals?
What are electrode potentials?
How can we determine if a redox reaction will occur using Table J?
What are the differences and similarities between voltaic and
electrolytic cell?
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Honors Chemistry
Ms. Argenzio
AIM: How can we assign
oxidation numbers?
Oxidation is defined as the loss of electrons
charge is increased).
(the
Reduction is defined as the gain of electrons (the
charge is reduced).
Helpful hint
LEO says GER
LEO – Loss of Electrons is Oxidation
GER – Gain of Electrons is Reduction
AIM: How can we assign
oxidation numbers?
Oxidation Numbers:
- all atoms are assigned oxidation numbers
(states)
- can be positive (metal in a compound),
negative (nonmetal in a compound), or
neutral (single atom)
- identify how many electrons are either gained
(nonmetals in a compound) or lost (metals in
a compound) by an atom or ion in a reaction
Rules for assigning oxidation numbers:
1. Any uncombined element has an oxidation state
of zero
2. Monatomic = atomic charge Na+Cl3. Group 1 metals = +1 in compounds
Group 2 metals = +2 in compounds
4. Fluorine is -1 in compounds
5. Halogens (Group 17) are -1 in compounds if
they’re the most electronegative element
6. Hydrogen is +1 in compounds but is -1 when
combined with a metal
Rules for assigning oxidation numbers:
7. Oxygen is -2 in compounds
Oxygen is +2 with fluorine (OF2) since fluorine
is more electronegative
Oxygen is -1 in H2O2 (hydrogen peroxide)
8. The sum of all oxidation states in compounds
is zero
9. The sum of all oxidation states in polyatomic
ions is the charge of the polyatomic ion
on the reference table (Table E)
CONCLUSION QUESTIONS!
DETERMINE THE OXIDATION NUMBERS
FOR EACH OF THE FOLLOWING:
1.N2
2.CO
3.FeO
4.NO
5.MgO
6.K
7.Fe2O3
8.CO2
9.NO2
CHALLENGE
1.Na2CO3
2.CaSO4
3.OF2
AIM: How can we recognize RedOx
reactions?
Redox reactions are used for electrochemistry
and are driven by a change in charge
Oxidation – more (+) charge
Reduction – more (-) charge
Redox Reaction types:
1. A + B  AB (Ex. 2H2 + O2  2H2O)
2. AB  A + B (Ex. 2NaCl  2Na + Cl2
3. A + BC  AC + B
(Ex. Zn + Cu(NO3)2  Zn(NO3)2 + Cu)
Rules for recognizing RedOx reactions:
1. If a single element is on either side of the equation
it must be a RedOx reaction
2. Assign oxidation numbers to all elements and see if
any have changed from reactant to product
3. If the oxidation number increased, it lost electrons,
therefore it was oxidized
4. If the oxidation number decreased, it gained
electrons, therefore it was reduced
Rules for Identifying Which Species is Oxidized
and Which Species is Reduced:
1. If charge becomes more (+) going from left to right
 oxidized & lost electrons
O
L
2. If charge becomes more (-) going from left to right
 reduced & gained electrons
R
G
Rules for Identifying Which Species is Oxidized
and Which Species is Reduced:
EX) Cu + 2AgNO3  Cu(NO3)2 + 2Ag
- Determine oxidation numbers for each
- If there is a polyatomic ion that remains constant on
both sides just look up the charge of the polyatomic ion
Agents: Species that is oxidized  reducing agent
Species that is reduced  oxidizing agent
Spectator ion: Ion that does not change its charge
Directions:
1. Assign oxidation states to each species in the reaction
2. Identify the species being oxidized and species being reduced
3. Identify the reducing agent, oxidizing agent, and spectator ion
(if there is one)
Ex1) Cu + O2  CuO
EX2) Al + Cl2  AlCl3
EX3) N2 + H2  NH3
EX4) H2 + O2  H2O
EX5) Na + CaCl2  NaCl + Ca
AIM: How can we write half
reactions?
Redox reactions may be split into 2 half-reactions, one
for oxidation and one for reductions
Examples:
Oxidation
Fe(s) -> Fe3+(aq) + 3eReduction
Fe3+(aq) + 3e- -> Fe(s)
Do NOW: For each of the following:
- Make sure each balanced
- Assign oxidation numbers
- Write the oxidation half rxn/reduction half rxn
- Identify the oxidizing agent and reducing agent
- Identify the spectator ion (if there is any)
EX1) 2Li +Zn(NO3)2  2LiNO3 +Zn
EX2) 2K + Cl2  KCl
EX3) SnCl2 + 2FeCl3  SnCl4 + 2FeCl2
ELECTROCHEMISTRY:
The branch of chemistry that deals with the relations between
electrical and chemical phenomena.
Electrochemical Cell
– Voltaic Cell
*Spontaneous
Electrolytic Cell
Electroplating
*Non Spontaneous
Redox Potentials and Metal/Non metal Activity
TABLE J
 The higher up a substance is the more reactive it is
 For metals the more reactive means higher potential
to be oxidized
 For non metals the more reactive means a higher
potential to be reduced
Ex) Which metal has the greatest potential to be
oxidized?
Ex) Which non metal has the greatest potential to be
reduced?
Redox Potentials and Metal/Non metal Activity
Ex) Which reaction is more likely to occur?
1. Cu+2 + Al0  Cu0 + Al+3
2. Cu0 +Al+3  Cu+2 + Al0
Redox Potentials and Metal Activity
Ex) Which reaction is more likely to occur?
1. Cl20 + 2F-1  2Cl-1 + F20
2. F20 +2Cl-1  2F-1 +Cl20
Wednesday 5/7/2014 A-Day
AIM: Electrochemistry
DO NOW: For each of the following:
1. Check to see if it is balanced
2. Assign Oxidation numbers
3. Determined the oxidized/reduced species/spectator ion
4. Write the oxidation and reduction half reactions
***WORK QUIETLY AND INDEPENDENTLY (USE
YOUR NOTES )****
EX 1) Al + O2  Al2O3
EX 2) Mg + ZnCl2  MgCl2 + Zn
VOLTAIC CELL: electrochemical cells in which
spontaneous chemical reactions produce a flow of
electrons
VOLTAIC CELL: electrochemical cells in which
spontaneous chemical reactions produce a flow of
electrons
PARTS OF A VOLTAIC CELL:
1. 2 half cells (2 beakers)
2. 2 electrodes (anode and cathode)
3. Salt Bridge – MIGRATION OF IONS!!! (upside down
U-TUBE)
4. Wire – flow of ELECTRONS!
5. Optional (voltmeter, switch)
AIM: How can we describe an electrochemical cell
DO NOW:
Using your notes from yesterday and your review books
Label the following voltaic cell
VOLTAIC CELL
RED CAT sat on AN OX
REDUCTION occurs at the CATHODE
OXIDATION occurs at the ANODE
Remember from Table J
- the higher metal will be oxidized; anode
- the lower metal is the site of reduction; cathode
**FLOW OF ELECTRONS IS ALWAYS FROM ANODE TO
CATHODE!!!!!***** (RED CAT GETS FAT)
ELECTROLYTIC CELL
Electrolysis: Electricity used to force a chemical
reaction to occur
ELECTROLYTIC CELL
Electroplating: Electrolysis can be used to
electroplate metals onto a surface