Redox Reactions

  • Created by: goliver3
  • Created on: 18-01-17 17:53

Oxidation & Reduction

  • Oxidation is the loss of electrons, reduction is the gain of electrons (OILRIG)
  • The oxidation number of an atom is the charge that would exist on an individual atom if the bonding was completely ionic
  • In molecules/compounds the sum of oxidation numbers of the atoms is zero
  • In complex ions, the sum of the oxidation numbers on the atoms is equal to the overall charge on the ion e.g. ClO-, oxidation number of Cl = +1, oxidation number of O = -2, +1 + (-2) = -1
  • All group I atoms adopt a +1 oxidation state in their compounds
  • All group II atoms adopt a +2 oxidation state in their compounds
  • Aluminium always adopts a +3 state
  • Fluorine always adopts a -1 state
  • Hydrogen adopts a +1 state, unless bonding to metal, silicon, or boron in which it adopts a -1 state
  • Oxygen adopts a -2 oxidation state unless bonded to a group I/II metal, or hydrogen, in which it adopts a -1 state, or which fluorine, in which it adopts a +2 state
  • The oxidation state of all other atoms varies depending on the compound
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Oxidation & Reduction 2

  • If an atom is oxidised its oxidation state increases
  • If an atom is reduced its oxidation state decreases
  • How to balance half equations
    • Indentify the atom being oxidised or reduced, make sure there are the same number of that atom on both sides
    • Balance O atoms by adding H2O
    • Balance H atoms by adding H+
    • Add the electrons to ensure the charge on both sides is the same
  • Oxidising agents accept electrons from other species
  • Reducing agents give away electrons to other species
  • The simultaneous oxidation and reduction of the same species is known as disproportionation
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Halogens & Halides

  • Elements in group VII - fluorine, chlorine, bromine, and iodine
  • Tend to form diatomic molecules - F2, Cl2, Br2, and I2
  • These form anions called halides
  • Boiling point increases down the group due to increase in strength of Van der Waal's forces
  • The electronegativity decreases down the group
  • All halogens are oxidising agents
  • Fluorine is the best oxidising agent, followed by chlorine
  • Halide ions are reducing agents
  • Iodide ions are the best reducing agents, followed by bromine ions
  • Fluoride ions have no significant reducing properties
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