Need to Know What is oxidation/reduction What is oxidizing or reducing agent Oxidation Numbers Balancing redox reactions ocus: Electrochemistry as a Chemical Analysis Tool MnO 4 - + NO 2 - Mn 2+ + NO 3 - What is reduced in the following equation a. Mn b. N c. O
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Need to KnowWhat is oxidation/reductionWhat is oxidizing or reducing agentOxidation NumbersBalancing redox reactions
Focus: Electrochemistry as a Chemical Analysis Tool
MnO4- + NO2
- Mn2+ + NO3-
What is reduced in the following equation
a. Mnb. Nc. O
Split into two reactionsCe4+ + e- = Ce3+ (Reduction)Fe2+ = Fe3+ + e- (Oxidation)
Electrochemical CellsGalvanic cell - cell in which the reactions occur
spontaneously to produce electrical energy
Electrolytic cell – electrical energy used to force a non-spontaneous reaction to occur
Cathode: where reduction takes placeAnode: where oxidation takes place
memorize
Two ways to make an electrochemical cell
1- all in same container
2- separate containers : half cellsconnect with bridge
Copper – oxidizedsoln blue
Silver – reducedCu turns grey
Piece of Cu ina soln of AgNO3
2Ag+ + Cus 2Ags + Cu2+
A “silver” xmas tree
Reaction: spontaneous
2Ag+ + 2e- 2AgsCds Cd2+ + 2e-anode cathode
Balanced rxn = ?
G0 = - nFE0 E0 = E0cath – E0
anode
E0 = ?
Reaction proceeds until “chemical equilibrium”
Cu + 2Ag+ Cu2+ + 2Ag
E0 = ?
From skoog, west, holler etal
Can not measure the potential of any half-cell rxn
Can measure Potential Difference
Establish a reference electrodetabulate wrt that half cell
Half cell Ref: SHE or NHE
1. Make SHE the anode
2. Make the other cell the cathode
3. Measure potential difference
2H+ + 2e- H2(g) E0 = 0.00 Vmemorize
E0 cell = E0 cathode - E0 anode
If E0 anode is 0then E 0
cell = E 0cathode
All reactions must be written as reduction rxns
SHEanode
E0cell = ?
What is E0 for5Fe3+ + 5e- = 5Fe2+
givenFe3+ + e- = Fe2+ E0 = 0.771 V
a. 0.771b. 3.86c. 0.154d. 0
MnO4- + NO2
- Mn2+ + NO3-
What is oxidizing agent in the following equation
a. MnO4-
b. NO2-
c. Mn
Important Points:
Simplified Cell Schematic
Anode ll Cathode
E0 cell = E0 cathode – E0 anode
All rxns written as reduction
ΔG0 = - nFE0
memorize
memorize
ΔG0 is negative: spontaneous
ΔG0 is positive: non-spontaneous
Which one of the following would be the best oxidizing agent