Redox definitions

Every term the lessons in this unit define, lesson by lesson, worded as the lessons use them. Each lesson title links to its notes.

26 terms

Oxidation states and the rules for assigning them

Oxidation: The loss of electrons by a species, which raises the oxidation state of one of its elements.
Reduction: The gain of electrons by a species, which lowers the oxidation state of one of its elements.
Redox reaction: A reaction in which one species is oxidised and another is reduced, with electrons transferred from one to the other.
Oxidation state: The charge an atom would have if all its bonds were ionic, with the bonding electrons assigned to the more electronegative atom.
Oxidation number: Another name for oxidation state: the same number, found by the same rules.
Peroxide: A compound containing an O–O single bond, such as H₂O₂ or Na₂O₂, in which each oxygen has an oxidation state of −1.
Metal hydride: A compound of a metal with hydrogen, such as NaH or CaH₂, containing H⁻ ions, in which hydrogen has an oxidation state of −1.
Oxidising agent: An electron acceptor: a species that oxidises another and is itself reduced.
Reducing agent: An electron donor: a species that reduces another and is itself oxidised.

Half-equation: An equation for either the oxidation or the reduction part of a redox reaction, balanced for atoms and charge, with electrons shown.
Spectator ion: An ion present in the reaction mixture that is unchanged by the reaction and is left out of the ionic equation.
Ionic equation: An equation showing only the species that take part in the reaction, with spectator ions left out, balanced for atoms and charge.
Disproportionation: A redox reaction in which the same element in one species is simultaneously oxidised and reduced.
Chloric(I) acid: HClO, the weak acid formed when chlorine reacts with water, in which chlorine has an oxidation state of +1.
Chlorate(I) ion: The ClO⁻ ion, in which chlorine has an oxidation state of +1; its sodium salt is the active ingredient of bleach.
Overall redox equation: The equation formed by adding an oxidation half-equation and a reduction half-equation with equal numbers of electrons, so that the electrons cancel.
Chlorate(V) ion: The ClO₃⁻ ion, in which chlorine has an oxidation state of +5; formed with chloride when chlorine reacts with hot, concentrated alkali.

Redox titration: A titration in which the reaction between the solution in the burette and the solution in the flask is a redox reaction.
Self-indicating: Describes a titration in which a reagent's own colour change shows the end point, so no separate indicator is added.
End point: The point in a titration at which the indicator, or the reagent itself, first shows a permanent colour change.
Autocatalysis: Catalysis of a reaction by one of its own products, so the rate increases as the product builds up.
Titre: The volume of solution added from the burette to reach the end point.
Concordant titres: Titres that agree with one another to within 0.10 cm³, which are the ones used to calculate the mean.
Primary standard: A substance pure and stable enough that a solution of accurately known concentration can be made by weighing it and dissolving it to a known volume.
Standard solution: A solution whose concentration is known accurately, used to find the concentration of another.
Percentage purity: The mass of the pure substance in a sample, as found by analysis, divided by the mass of the sample, multiplied by 100.