CH5 (Redox and Electrochemistry)

This resource should hopefully contain the basic information required for the first topic in CH5 WJEC. I hope this is useful. Good luck :)

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Define Oxidation
Loss of electrons
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Define Reduction
Gain of electrons
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Oxidation Is Loss Reduction Is Gain
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Oxidation state for an element?
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What is redox?
This is when one species is being oxidized in a reaction and one species is being reduced.
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What does the salt bridge do in an electrochemical cell?
Completes the circuit and allows ions to move without the two solutions mixing.
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What does the high resistance voltmeter do in an electrochemical cell?
This gives the EMF reading for the cell.
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What is the standard electrode potential?
This is the potential difference when any half cell is connected to the standard hydrogen electrode under standard conditions.
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A metal solution half cell
A piece of metal acting as an electrode dipping into a solution containing ions of the same metal i.e. Cu I Cu2+
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A gas solution half cell
A gas is bubbled over an inert platinum electrode dipping in a solution containing ions of the gas i.e. X2(g) I X-(aq)
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A mixed ion half cell
This cell uses an inert platinum electrode, this electrode is placed in a solution containing different ions of the same element in different oxidation states i.e. Fe2+,Fe3+ A comma is used as both ion are in the same physical state.
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Working out Standard electrode Potentials
The more positive the standard electrode potential the more likely the system is to gain electrons. The standard potential of the cell is the more positive potential minus the less positive potential.
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How to work out if the standard electrode potential cell is feasible
The EMF has to be positive for the reaction to be feasible. To calculate the EMF you subtract the Standard electrode potential for oxidation from reduction. (Reduction - oxidation)
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Joining half equation in redox reactions
You will have two half equations, one for the oxidation and one for the reduction. You may have to multiply one of the reactions through, to get like variables that can then be canceled when we merge the two half equation.
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concentration Volume and mols calculations
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What is stoichiometry?
The reacting ratio
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Oxidation of Fe2+ by acidified manganate (VII) (MnO4-)
MnO4- + 8H+ + 5Fe2+ -- Mn2+ + 4H2O + 5Fe3+ Reacting ratio is therefore 1MnO4- : 5Fe2+ (1:5)
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Oxidation of Fe2+ by acidified dichromate (VI) (Cr2O7 2-)
Reacting ratio 1Cr2O7 2-:6Fe2+ (1:6)
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Uses of Redox reactions in organic synthesis
Oxidation of alcohols to aldehydes, ketones or carboxylic acids using acidified potassium dichromate(VI). Reduction of nitriles to amines using lithium tetrahydriodoaluminate(III). Reduction of nitrobenzene to phenylamine using tin and HCl.
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Fuel cells process?
At one platinum electrode hydrogen is oxidized to H+ ions, whilst at the other platinum electrode oxygen gas is reduced to water.
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Advantages of fuel cells?
No CO2, only bi-product is water. Efficient as less energy is lost as heat. Hydrogen gas can be produced using renewable resources such as electrolysis of water.
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Disadvantages of fuel cells?
Hydrogen is highly flammable and is therefore difficult to store. Hydrogen gas is usually produced from fossil fuels, which leads to a net energy loss.
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Other cards in this set

Card 2


Define Reduction


Gain of electrons

Card 3




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Card 4


Oxidation state for an element?


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Card 5


What is redox?


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