A comprehensive compilation of notes required for the electrochemistry section of the matric IEB Physical Science paper 2 (chemistry). Includes Galvanic cells, electrolytic cells, oxidation numbers, electroplating, electro-refining, quantitative aspects of electrochemistry, recovery of aluminium fr...
ELECTROCHEMISTRY NOTES Lucy van der Meulen
Definitions:
Redox reaction - a reaction involving the transfer of electrons
Oxidation - the loss of electrons
Reduction - the gain of electrons
Oxidising agent - a substance that accepts electrons
Reducing agent - a substance that donates electrons
Anode - the electrode where oxidation takes place
Cathode - the electrode where reduction takes place
Electrolyte - a substance that can conduct electricity by forming free ions when molten or dissolved in solution
Spectator ions - ions which are not involved in electron transfer
OXIDATION NUMBERS
1. In free and diatomic elements each atom has an oxidation number of zero (H2, Br2, K, S and O2)
2. In a neutral molecule, the sum of all the oxidation numbers must be zero
Example: K2Cr2O7
= 2(+1) 2(+6) 7(-2) = 0
3. In an ion, the sum of all the oxidation numbers must be equal to the charge of the ion.
Example: NH4+
= (-3) 4(+1) = +1
● NB: Sulfur has an unpredictable oxidation number
● Oxidation numbers are determined by the group that the element is in (work it out last)
● You can use the ion to work out the oxidation number - example: (NO3)-
Redox reactions: Reduction, Oxidation, Reducing and Oxidising Agents
Oxidation - the loss of electrons and this takes place at the anode (AN OX)
Reduction - the gain of electrons and this takes place at the cathode (RED CAT)
Oxidising Agent -a substance that accepts electrons
Reducing agent - a substance that donates electrons
Spectator ions - ions which are not involved in electron transfer
1
, THE STANDARD ELECTRODE POTENTIAL
● The reactions show only the ions involved in the transfer of electrons (no spectator ions)
● The reactions are shown as reversible half reactions
● Reduction processes when reading from left to right
● Oxidation reaction read from right to left
● Substances on the left are oxidising agents
● Substances on the right are reducing agent
ELECTROCHEMICAL REACTIONS
Electrochemistry - the branch of chemistry that deals with the transformation between electrical energy and
chemical energy
Galvanic Cells - chemical energy is transformed into electrical energy. This is a spontaneous chemical reaction
which generates an electric current
Electrolytic Cells - electrical energy is transformed into chemical energy. The electrical current drives a
non-spontaneous chemical reaction
Electrochemical processes - redox reactions in which electrons are transferred between substances.
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