Half Cell / redox potentials
Context
Students often struggle when asked to apply redox potentials and to combine reduction half equations correctly.
This activity aims to involve all the individuals in a group at once and in a mutually supportive way.
Task
Give each student one or two of the half cell cards and pair them up.
Between them they randomly put the cards into pairs, then answer the questions, swap cards, and pair up with a different
student.
Evaluation
This is a simple task but students were absorbed and usefully focused on this for around 40 minutes.
Can extend by asking the pairs to draw labeled diagrams of the cell formed or by giving full explanations as to why the
proposed overall reaction is feasible.
[original Reference http://www.rsc.org/learn-chemistry/resource/res00000240/chem-it-halfcell-activity]
© Royal Society of Chemistry 2015
MnO4- + 4H+ + 3e- ⇌ MnO2 + 2H2O
Eo = + 1.63 V
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reduction or oxidation half cell
positive or negative electrode
identify the oxidising or reducing agent
write the overall reaction equation
calculate Eocell
direction of electron flow
effect on Eocell of increasing [MnO4-]
K+ + e- ⇌ K
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reduction or oxidation half cell
positive or negative electrode
identify the oxidising or reducing agent
calculate Eocell
direction of electron flow
effect on Eocell of increasing temperature if
the overall cell reaction is exothermic
Ca2+ + 2e- ⇌ Ca
F2 + 2e- ⇌ 2F
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Eo = - 2.76 V
Eo = + 2.85 V
reduction or oxidation half cell
positive or negative electrode
identify the oxidising or reducing agent
write the overall reaction equation
calculate Eocell
direction of electron flow
effect on Eocell of increasing [F-]
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Pb4+ + 2e- ⇌ Pb2+ Eo = + 1.79 V
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Eo = - 2.92 V
reduction or oxidation half cell
positive or negative electrode
identify the oxidising or reducing agent
write the overall reaction equation
calculate Eocell
direction of electron flow
effect on Eocell of increasing [Pb4+]
© Royal Society of Chemistry 2015
reduction or oxidation half cell
positive or negative electrode
identify the oxidising or reducing agent
write the overall reaction equation
calculate Eocell
direction of electron flow
effect on Eocell of increasing temperature
if the overall cell reaction is exothermic
Mg2+ + 2e- ⇌ Mg Eo = - 2.40 V
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reduction or oxidation half cell
positive or negative electrode
identify the oxidising or reducing agent
calculate Eocell
direction of electron flow
effect on Eocell of decreasing temperature
if the overall cell reaction is exothermic
Pt2+ + 2e- ⇌ Pt Eo = + 1.60 V
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reduction or oxidation half cell
positive or negative electrode
identify the oxidising or reducing agent
write the overall reaction equation
calculate Eocell
direction of electron flow
effect on Eocell of decreasing [Pt2+]
Al3+ + 3e- ⇌ Al
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MnO4- + 8H+ + 5e- ⇌ Mn2+ + 4H2O
Eo = + 1.63 V
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reduction or oxidation half cell
positive or negative electrode
identify the oxidising or reducing agent
write the overall reaction equation
calculate Eocell
direction of electron flow
effect on Eocell of decreasing [MnO4-]
reduction or oxidation half cell
positive or negative electrode
identify the oxidising or reducing agent
calculate Eocell
direction of electron flow
effect on Eocell of decreasing temperature
if the overall cell reaction is endothermic
V2+ + 2e- ⇌ V
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Eo = - 1.66 V
Eo = - 1.20 V
reduction or oxidation half cell
positive or negative electrode
identify the oxidising or reducing agent
write the overall reaction equation
calculate Eocell
direction of electron flow
effect on Eocell of decreasing [V2+]
Zn2+ + 2e- ⇌ Zn Eo = - 0.76 V
Hg2+ + 2e- ⇌ Hg Eo = + 0.86 V
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reduction or oxidation half cell
positive or negative electrode
identify the oxidising or reducing agent
write the overall reaction equation
calculate Eocell
direction of electron flow
effect on Eocell of decreasing [Hg2+]
© Royal Society of Chemistry 2015
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reduction or oxidation half cell
positive or negative electrode
identify the oxidising or reducing agent
calculate Eocell
direction of electron flow
effect on Eocell of decreasing temperature
if the overall cell reaction is exothermic
Cr3+ + 3e- ⇌ Cr
Cl2 + 2e- ⇌ 2CI- Eo = + 1.38 V
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reduction or oxidation half cell
positive or negative electrode
identify the oxidising or reducing agent
write the overall reaction equation
calculate Eocell
direction of electron flow
effect on Eocell of increasing Cl2 pressure
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Cr2O72- + 14H+ + 6e- ⇌ 2Cr3+ + 7H2O
Eo = + 1.30 V
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reduction or oxidation half cell
positive or negative electrode
identify the oxidising or reducing agent
write the overall reaction equation
calculate Eocell
direction of electron flow
effect on Eocell of decreasing [Cr3+]
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reduction or oxidation half cell
positive or negative electrode
identify the oxidising or reducing agent
write the overall reaction equation
calculate Eocell
direction of electron flow
effect on Eocell of decreasing [MnO4-]
© Royal Society of Chemistry 2015
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Eo = - 0.44 V
reduction or oxidation half cell
positive or negative electrode
identify the oxidising or reducing agent
write the overall reaction equation
calculate Eocell
direction of electron flow
effect on Eocell of decreasing [Fe2+]
Cr3+ + e- ⇌ Cr2+
MnO2 + 4H+ + 2e- ⇌ Mn2+ + 2H2O
Eo = + 1.35 V
reduction or oxidation half cell
positive or negative electrode
identify the oxidising or reducing agent
calculate Eocell
direction of electron flow
effect on Eocell of decreasing temperature
if the overall cell reaction is endothermic
Fe2+ + 2e- ⇌ Fe
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Eo = - 0.51 V
Eo = - 0.41 V
reduction or oxidation half cell
positive or negative electrode
identify the oxidising or reducing agent
write the overall reaction equation
calculate Eocell
direction of electron flow
effect on Eocell of increasing [Cr2+]
V3+ + e- ⇌ V2+
Br2 + 2e- ⇌ 2Br- Eo = + 1.07 V
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reduction or oxidation half cell
positive or negative electrode
identify the oxidising or reducing agent
write the overall reaction equation
calculate Eocell
direction of electron flow
effect on Eocell of increasing [Br-]
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reduction or oxidation half cell
positive or negative electrode
identify the oxidising or reducing agent
write the overall reaction equation
calculate Eocell
direction of electron flow
effect on Eocell of decreasing [Hg2+]
Ag+ + e- ⇌ Ag
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Eo = + 0.81 V
reduction or oxidation half cell
positive or negative electrode
identify the oxidising or reducing agent
write the overall reaction equation
calculate Eocell
direction of electron flow
effect on Eocell of decreasing [Ag+]
© Royal Society of Chemistry 2015
reduction or oxidation half cell
positive or negative electrode
identify the oxidising or reducing agent
calculate Eocell
direction of electron flow
effect on Eocell of decreasing temperature
if the overall cell reaction is endothermic
Ni2+ + 2e- ⇌ Ni
Hg2+ + 2e- ⇌ Hg Eo = + 0.86 V
Eo = - 0.26 V
reduction or oxidation half cell
positive or negative electrode
identify the oxidising or reducing agent
write the overall reaction equation
calculate Eocell
direction of electron flow
effect on Eocell of increasing [Ni2+]
Sn2+ + 2e- ⇌ Sn
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Eo = - 0.25 V
Eo = - 0.14 V
reduction or oxidation half cell
positive or negative electrode
identify the oxidising or reducing agent
write the overall reaction equation
calculate Eocell
direction of electron flow
effect on Eocell of increasing [Sn2+]
- -o
EoV= + 1.07 V
I2 + 2e-Br
⇌2 +2I2e
E⇌=2Br
+ 0.58
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2H+ + 2e- ⇌ H2
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 reduction
or oxidation
half cell
reduction
or oxidation
half cell

 positive
or negative
electrode
positive
or negative
electrode
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identify
the
oxidising
or
reducing
agent
identify the oxidising or reducing agent
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 the
write
the overall
reaction
equation 
write
overall
reaction
equation
 calculate
calculate
Eocell Eocell
 direction
of electron
direction
of electron
flow flow
o
o
 effect
effect
on E cellonofEdecreasing
[I-] [Br-]
cell of increasing
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reduction or oxidation half cell
positive or negative electrode
identify the oxidising
reducing
Ag+ + e- ⇌orAg
Eo = +agent
0.81 V
write the overall reaction equation
calculate Eocell
direction of electron flow
 reduction
oxidation[Fe
half
2+ cell
effect
on Eocell of or
decreasing
]
 positive or negative electrode
 identify
the oxidising or reducing agent
Cu2+ + 2e- ⇌ Cu Eo = + 0.34 V
 write the overall reaction equation
 calculate Eocell
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 direction of electron flow

o
+
 effect
E cell of decreasing
reduction
oron
oxidation
half cell [Ag ]
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positive or negative electrode
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identify the oxidising or reducing agent
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write the overall reaction equation
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calculate Eocell

direction of electron flow
effect on Eocell of decreasing [Cu2+]
© Royal Society of Chemistry 2015
reduction or oxidation half cell
positive or negative electrode
identify the oxidising or reducing agent
calculate Eocell
direction of electron flow
effect on Eocell of decreasing temperature
if the overall cell reaction is
endothermic
Cu2+ + e- ⇌ Cu+
Fe3+ + e- ⇌ Fe2+ Eo = + 0.75 V
Eo = 0.00 V
Eo = + 0.17 V
reduction or oxidation half cell
positive or negative electrode
identify the oxidising or reducing agent
write the overall reaction equation
calculate Eocell
direction of electron flow
effect on Eocell of increasing [Cu2+]
Sn4+ + 2e- ⇌ Sn2+ Eo = + 0.20 V
reduction or oxidation half cell
positive or negative electrode
identify the oxidising or reducing agent
write the overall reaction equation
calculate Eocell
direction of electron flow
effect on Eocell of increasing [Sn2+]