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Redox Basics• Redox Reactions
happen when – one substance loses
electrons (oxidized) and – one gains electrons
(reduced)• Electrons are flowing Cl2
2Na2Cl-
2Na+
2 Electrons
Half equation #1: 2Na 2Na+ + 2e-
Half equation #2: Cl2 + 2e- 2Cl-
nett: 2Na + Cl2 2Na + 2Cl-
Example Reaction
Zn + Cu2+ Cu + Zn2+
Gains 2 electrons- reduced
Loses 2 electrons- oxidized
Cu2+
Zn
Zn2+
CuZn Zn2+ = +0.76
Cu2+ Cu = +0.34
Overall = +1.10
Harness Electrons• If the reactants are separated
• The electrons cannot travel directly between reactants
• Those electrons can be used to do work
• Note: the electrons will always flow in the direction which gives a +Eo
cell
• Eocell = Eo(red)-Eo(ox)
SO42-
Zn2+
CuZn
Reaction:
Zn + CuSO4 Cu + ZnSO4
Build a Cell 1 (Ch 20, sect 3)
SO42- Cu2+
Electrode-
carries electro
ns, may or
may not be part of
the reactio
n
Reaction:
Zn + Cu2+ Cu + Zn2+
Zn2+
CuZn
Reaction:
Zn + Cu2+ Cu + Zn2+
Electrons!
Build a Cell 3
Cu2+
Salt BridgeKCl
K+Cl-Cu
Zn
Build up of + ions
Build up of - ions
Terminology• Electrode: conductor which allows electrons to
enter or leave a cell (any conductive but unreactive material, sometimes part of the redox reaction)
– Anode: oxidation electrode, negative (Zn)– Cathode: reduction electrode, positive (Cu)
• Half-cell: half of the electrochemical cell where ox. or red. takes place.
• Electrolyte: salt solution in a half-cell, always contains oxidized and reduced form
PtC
Reaction:
Cl- + MnO4- Cl2 + Mn2+
10Cl- + 2MnO4- + 16H+ 5Cl2 + 2Mn2++ 8H2O
Electrons!
Other Cells 3
Cl-
MnO4-/H+
Cl2 Mn2+
e- e-
Salt bridge
Try it!• Draw a cell schematic to show the reaction:
Cu Cu2+ + 2e-
I2 + 2e- 2I- (platinum electrode)
Cu + I2 Cu2+ + 2I-
• Label the anode, cathode, and direction of electron flow
• Calculate the voltage
PtCu
Cu + I2 Cu2+ + 2I-
Electrons!
Try It! Answer
Salt bridge
Cu2+
I2
Anode- oxidationCathode- reduction
Voltage = -0.34 + 0.54 = 0.20V
Videos• Galvanic cells (2 min)• Animation (24 sec)• Li Batteries (5.5 min)• Potentials (2 min)• Song (3.5 min, This guy is seriously prolific)