3.1.11 3.1.11 Electrode potentials and electrochemical cells (A-level only)
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What are the components of an electrochemical cell? [4]:
• 2 half cells joined by a wire • Voltmeter • Salt bridge
How does a salt bridge work?
It has mobile ions which can conduct a charge (allows ions to flow through)
What is a salt bridge usually made from?
Piece of filter paper soaked in a salt/potassium nitrate
What is a property that the salt in the salt bridge is required to have?
Must be unreactive with the electrodes and electrode solutions
Why do we not use a wire instead of a salt bridge?
because the metal wire would set up its own electrode system with the solutions
Why is a high resistance voltmeter used? [2]:
• The voltmeter needs to be of very high resistance to stop the current from flowing in the circuit. • In this state, it is possible to measure the maximum possible potential difference (E)
How is potential difference measured?
With a high resistance voltmeter
E=
Potential difference
The Oxidation reaction is the
most negative one
OILRIG
Oxidation is loss of electrons and hydrogen, reduction is gain
Why does voltage form in a cell? [3]:
• The half cell that is oxidised releases electrons • More electrons will build up on the oxidised electrode than the reduced electrode • A potential difference is created between the two electrodes
What will the most positive electrode always undergo?
Reduction
What will the most negative electrode always undergo??
Oxidation
What is used when a system does not include a metal that can act as an electrode?
A Platinum electrode
Why is a platinum electrode used? [3]:
• Provides a conducting surface for electrons to transfer • Unreactive • conducts electricity
What is an electrochemical cell =
2 half cells joined together
Why do we flip the oxidation reaction?
Oxidation is loss so we flip to show the electrons being lost
What is electrode potential measured in?
Volts
What do you do to get the overall cell equation?
Reduction equation + FLIPPED oxidation equation
What are the standard conditions for standard hydrogen electrode potential E° [3]:
• 298K • 100kPa • 1.00 mol dm⁻³
What is the standard hydrogen electrode (SHE) used for?
used as a reference to measure standard electrode potentials
What is the E° of the SHE
0.00V
What is E° measured in?
Volts
standard electrode potential equation:
E° = E° reduced - E° oxidised