REDOX

Classical Oxidation

The gain of oxygen or removal of hydrogen in a chemical reaction.

Classical Reduction

The loss of oxygen or gain of hydrogen in a chemical reaction.

Modern Oxidation

The loss of electrons by a chemical species.

Modern Reduction

The gain of electrons by a chemical species.

Oxidation Number

The theoretical charge an atom would have if all bonds were purely ionic.

Disproportionation

A reaction where a single reactant is simultaneously oxidised and reduced.

Oxyanion Suffixes (-ate vs -ite)

'-ate' indicates a high oxidation state; '-ite' indicates a lower oxidation state.

Oxyanion Prefixes (hypo- vs hyper-)

'Hypo-' means the lowest state (one less than -ite); 'hyper-' means highest state.

Balancing Half-Equations (Oxygen & Hydrogen)

Balance oxygen using H₂O molecules and hydrogen using H⁺ ions.

Balancing Half-Equations (Charge)

Conserve charge by adding electrons; electrons appear on reactants for reduction.

Metal Displacement Reaction

A reactive solid metal displaces ions of a less reactive metal from solution.

Halogen Displacement Reaction

A more reactive halogen molecule displaces less reactive halide ions from solution.

Combustion Reaction

A combustible species reacts with oxygen in a highly exothermic redox reaction.

Oxidising Agent

A substance that is reduced and brings about oxidation; has a high tendency to take electrons.

Reducing Agent

A substance that is oxidised and brings about reduction; has a high tendency to lose electrons.

Reaction Spontaneity

A redox reaction occurs spontaneously if the overall standard cell potential is positive.

Galvanic Cell

An electrochemical cell that converts chemical energy from spontaneous redox reactions into electrical energy.

Galvanic Cell Anode

The electrode where oxidation occurs; source of electrons flowing to the cathode.

Galvanic Cell Cathode

The electrode where reduction occurs; destination for cations in solution.

Salt Bridge

Completes the circuit in a galvanic cell by allowing ion movement between half-cells.

Standard Cell Conditions

1 mol L⁻¹ solution concentration

Standard Hydrogen Electrode (SHE)

The universal reference standard in electrochemistry with a defined potential of 0.00 V.

Primary vs Secondary Cells

Primary cells cannot be effectively recharged; secondary cells are rechargeable.

Leclanché Dry Cell

A primary zinc-carbon cell with a zinc anode and carbon/MnO₂/NH₄Cl paste cathode.

Alkaline Battery

A primary cell using KOH electrolyte instead of NH₄Cl to sustain higher currents.

Lead-Acid Battery

A rechargeable secondary cell with lead anodes

Lithium-Ion Battery

A secondary cell with high energy density using lithium ions intercalated in graphite.

Fuel Cell

An electrochemical cell that requires a continuous external supply of reactants like fuel and oxygen.

Direct (Dry) Corrosion

The direct chemical reaction of metals with environmental oxygen to form metal oxides.

Rusting of Iron

The corrosion of iron requiring both oxygen and moisture to form hydrated iron(III) oxide.

Differential Aeration Principle

Localised corrosion caused by varying oxygen concentrations across a metal surface.

Sacrificial Protection

Coating metal with a more reactive metal that oxidises in preference

Cathodic Protection

Protecting a metal by connecting it to the negative pole of a power source to force reduction.

Electrolysis

Using electrical energy to force a non-spontaneous chemical reaction to proceed.

Aqueous Electrolysis Competition

In aqueous solutions

Electroplating

Coating a thin layer of metal onto an object by making the object the cathode in electrolysis.

Electrorefining of Copper

Purifying blister copper using an impure copper anode

Downs Cell

An industrial electrolytic cell used to produce molten sodium metal from molten NaCl.

Hall-Héroult Process

The industrial production of aluminium via electrolysis of alumina dissolved in molten cryolite.