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AQA
Physical
3.1.11 - Electrode potentials
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Paul Evangelou
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Cards (29)
What is the purpose of the salt bridge in an electrochemical cell? allows
ions
to
flow
to complete the
circuit
What is the salt bridge made up of in an electrochemical cell?
filter paper
soaked in
KNO3
cell
EӨ values are always quoted for
reductions
Soluble ionic compound used in a salt bridge must
not react
with
electrolyte
in beaker
Reactions
are written in the electrochemical series as
reductions
An
oxidising
agent will oxidise anything that is in the electrochemical series
above
Reasons an expected reaction would not happen in a cell:
Kinetically stable
Solution
too dilute
What are the three types of cells?
Rechargeable
Non-rechargeable
Fuel
Advantages of
non-chargeable
batteries:
Cheaper to buy
Work for longer
Can be recycled
Don't contain toxic Pb / Cd so less dangerous in landfill
What are the advantages of
rechargeable
batteries?
Can be reused so cheaper long term
Can be recycled
What are the advantages of
fuel cells
?
No recharging needed
H2O is only product
What are the disadvantages of fuel cells?
Expensive as H2 produced by
electrolysis
of water
H2 highly
flammable
Features of the electrochemical series:
Oxidising
agents on the left
Reducing
agents on the right
Most powerful oxidising agent on the bottom
left
Most powerful reducing agent on top
right
Salt bridges are necessary to:
Complete
the
circuit
Allows
ion movement
to
balance
the charge. Do not react with electrodes
What type of species goes is furthest from the salt bridge in standard cell notation?
The most
reduced species
What does | indicate?
Phase boundary
(solid/liquid/gas)
What happens at the left-hand electrode?
Left hand electrode is where
oxidation
occurs.
Left hand electrode is the
half cell
with the most
negative
Eo value
Right hand electrode:
right hand electrode is where
reduction
occurs.
Right hand electrode is the half cell with the most
positive
Eo value
Which side of the cell has the most negative Eo value?
Left hand
electrode
Label this standard hydrogen electrode
A)
High resistance voltmeter
B)
Platinum wire
C)
Hydrogen Gas
D)
Salt bridge
E)
Porous platinum metal
F)
Dilute Acid
6
What conditions is the standard hydrogen electrode used in?
Temperature =
298 K
Pressure =
100 kPa
[
H
+ ] =
1.00
mol
dm-3
Why might you use other standard electrodes occasionally?
They are cheaper/easier/quicker to use and can provide just as good a reference.
Platinum
is expensive
If an Eo value is more negative, what does it mean in terms of oxidising/reducing power? Better
reducing
agent (easier to oxidise)
What factors will change Eo values?
Concentration
of
ions
Temperature
When would you use a
Platinum
electrode? When both the oxidised and reduced forms of the metal are in
aqueous
solution
Why is
Platinum
chosen?
Inert
so does not take part in the electrochemistry
Good conductor to
complete circuit
Where are
lithium-ion
cells used? Mobile phones and Laptops
A
fuel cell
is a cell that is used to generate
electric current
; does not require electrical
recharging
Label this diagram of a hydrogen fuel cell
A)
Anode
B)
Electrolyte
C)
Cathode
D)
h2
E)
o2
F)
h20
6