Chemistry AS CI 9.1

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  • Created by: A.B.
  • Created on: 17-02-14 13:15
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  • ES Oxidation and Reduction CI 9.1
    • When an oxidation and a reduction reaction occur simultaneously, this is called a redox reaction.
    • Oxidation can be defined by:
      • Loss of Electrons
      • Oxidation state increasing (becomes more positive)
    • Reduction can be defined by:
      • Gain of Electrons
      • Oxidation state decreasing (becomes more negative)
    • Assigning Oxidation States
      • The ATOMS in ELEMENTS are always in an oxidation state of 0
      • In COMPOUNDS or IONS, oxidation states are assigned to each atom or ion. Since COMPOUNDS have NO overall charge, the OXIDATION state must ADD up to ZERO. In IONS the OXIDATION state adds up to the CHARGE on the ION.
      • Some atoms rarely change their oxidation states in reactions. These can be used to help assign oxidation states to other species.
        • F = -1
        • O = -2 (except in O2- and OF2)
        • H = +1
        • Cl = -1 (except with O or F)
    • Using Oxidation States
      • Can be used to tell if oxidised or reduced (oxidised -> increased, reduced -> decreased)
    • Oxidation states in names
      • When compounds contain elements that exist in more that one oxidation state the systematic name includes the oxidation number in roman numerals.
      • Oxyanions (negative ions that contain oxygen and another element) have -ate and oxidation state of element that isn't oxygen
    • Electron transfer and Half Equations
      • Redox reactions can be written as two separate half equations, one oxidation and one reduction
    • Other redox changes with halide ions
      • A displacement reaction occurs when a more reactive halogen is placed into a solution of a less reactive halogen.


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