CHEM10006 Lecture Notes - Lecture 80: Lone Pair, Dont, Iron Ore
31 May 2018
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Monday, 15 May 2017
Redox Chemistry
Redox Reactions
Important in a variety of contexts:
Photosynthesis
Biosensors (glucose in blood), batteries
OILRIG —> Occur together: Redox
Oxidation numbers —> keeping track of electrons
Oxidant - Causes oxidation (is reduced)
Reductant- Causes reduction (is oxidised)
When oxidation number increases (oxidation), when it decreases (reduction)
Split into half-equations
Galvanic Cells
Release of energy
Can be captured due to current flow (one element has a greater tendency to be
reduced)
!1
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Monday, 15 May 2017
Quantitatively expressed as a cell potential
Daniell cell- zinc-copper (cell potential E= 1.10 V)
Can predict cell potential by knowing half cell
reduction potentials
Can take difference of reduction or add the oxidation
and reduction numbers
Reduction occurs at cathode (+ve galvanic)
Oxidation occurs at the anode (-ve galvanic)
Elections flows from negative electrode to positive electrode
Salt-bridge allows ion movement between the half-cells, preventing a build up
of charge
DON’T MULTIPLY CELL POTENTIAL
-ve ions in salt bridge to anode
+ve ions in salt bridge to cathode
!2
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Monday, 15 May 2017
Cell potential and equilibrium constants
Concentration differences occur across cell membranes leading to a potential
difference.
Reaction proceeds until system is at equilibrium (cell potential = 0 V, K (equilibrium
constant=Q)
Current will flow until concentrations are equal (two cells, same species, different
concentrations, one will reduce one will oxidise)
Concentration differences occur across cell membranes leading to a potential
difference
Membrane potentials normally between -40 to -80mv.
Reference Electrodes
NOTES DO
!3
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Document Summary
When oxidation number increases (oxidation), when it decreases (reduction) Can be captured due to current ow (one element has a greater tendency to be reduced) Daniell cell- zinc-copper (cell potential e= 1. 10 v) Can predict cell potential by knowing half cell reduction potentials. Can take difference of reduction or add the oxidation and reduction numbers. Elections ows from negative electrode to positive electrode. Salt-bridge allows ion movement between the half-cells, preventing a build up of charge. Reaction proceeds until system is at equilibrium (cell potential = 0 v, k (equilibrium constant=q) Current will ow until concentrations are equal (two cells, same species, different concentrations, one will reduce one will oxidise) Concentration differences occur across cell membranes leading to a potential difference. Potentials at intermediate ph"s (nernst equation under standard conditions) Plot will be straight line with gradient -0. 0591. Range of values of potential and ph for which water is thermodynamically stable.
