Unit 11: Redox

Redox

Refers to a chemical reaction in which there is a change in oxidation state of atoms

Reduction

The gain of electrons by an element during a reaction.

Oxidation

The loss of electrons by an element during a reaction.

LEO the lion says GER

A mnemonic device: Lose Electrons Oxidation, Gain Electrons Reduction.

Oxidation state of singular elements

All singular elements have an oxidation state of 0.

Oxidation state of an ion

The oxidation state of an ion is the same as the charge of the ion.

Oxidation state of Group 1 metals

Group 1 metals have an oxidation state of +1.

Oxidation state of Group 2 metals

Group 2 metals have an oxidation state of +2.

Oxidation state of Oxygen

Oxygen has an oxidation state of -2, except in peroxides where it is -1.

Oxidation state of Fluorine

Fluorine has an oxidation state of -1.

Balancing Half Reactions

Electrons lost must equal electrons gained in a balanced equation.

Electrons in Oxidation Half Reactions

Electrons are lost and written as a product.

Electrons in Reduction Half Reactions

Electrons are gained and written as a reactant.

Overall Balanced Redox Reaction

Combine both half reactions, omitting species that are reactants and products.

Voltaic Cell

Converts chemical energy into electrical energy. Spontaneous

Electrolytic Cell

Converts electrical energy into chemical energy. Nonspontaneous

Flow of electrons

Electrons flow from anode to cathode in both types of cells.

Spontaneous Reaction

A reaction that occurs without external energy input.

Nonspontaneous Reaction

A reaction that requires external energy input.

Cathode in Voltaic Cells

The electrode where reduction occurs; it gains mass.

Anode in Voltaic Cells

The electrode where oxidation occurs; it loses mass.

Activity Series

A list of elements arranged by their reactivity; higher elements are more likely to lose electrons.

Half Reaction for Copper Oxidation

Cu0 (s) → Cu2+ (aq) + 2e-.

Half Reaction for Silver Reduction

Ag+ (aq) + e- → Ag0 (s).

Charge Conservation

The total charge of reactants must equal the total charge of products in a reaction.