A Level Edexcel Chemistry - Topic 14 - Redox 2/II
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Topic 14 - Redox 2
Electrochemical cells
What are electrochemical cells made up of?
electrochemical cells are made from two different metals dipped in salt solutions
of their own ions and connected by a wire
Explain the electrodes in an electrochemical cells and what happens at them
electrodes are opposite to electroylsis
anode = negative cathode = positive
oxidation happens at the cathode and reduction at the anode
the more reactive form ions more readily so it gives up its electrons and is
oxidised (so it becomes the anode, where electrons flow from)
the less reactive metal becomes the cathode
Explain the setup and what happens in the zinc/copper electrochemical cell
zinc loses electrons more easily than copper, so in the left half cell, zinc is
OXIDISED to form Zn2+ ions
this releases electrons to the external circuit
in the other half cell, the same number of electrons are taken from the
external circuit, REDUCING the Cu2+ ions to form copper atoms
Describe the purpose of the salt bridge that connects the two half cells
salt bridge is made of filter paper soaked in salt solution - KNO3
the salt ions flow through the salt bridge to complete the cell, and balance out
the chargers in the beakers
Explain how you can have half cells involving solutions of two aqueous ions
of the same element, such as Fe2+ and Fe3+
happens on the surface of the electrode
Topic 14 - Redox 2 1
, neither the reactants or products are solid you use platinum or graphite for the
electrode
it needs to conduct electricity and be very inert so that it wont react with
anything
Electrode potentials
Explain how a potential difference builds up in half cells and relate to the zinc
half cell
as the substances are oxidised or reduced
due to the difference in charge between the electrode and the ions in the
solution
in the zinc half cell, the Zn electrode is negatively charged due to the
electrons left behind wehn ions form and the Zn2+ ions are postively
charged
Explain what the electrode potentials of the half cells determines
the zinc half cell has a more negative E value, so zinc is oxidised(the
reaction goes backwards)
copper is reduced (the reaction goes forward)
Define the standard electrode potential
The standard electrode potential of a half cell is the voltage measured under
standard conditons when the half cell is connected to a standard hydrogen
electrode
Draw how you would set up the apperatus to measure standard electrode
potential with the standard hydrogen electrode
temp = 298K , 25*C
Topic 14 - Redox 2 2
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