20de01e95640320319ed0403122c092b02990d6b
   1# Electrochemistry
   2
   3## Oxidation states
   4
   5Indicates charge (ionisation) of an element
   6
   7**Oxidation** - loss of e- (at anode)  
   8**Reduction** - gain of e- (at cathode)
   9
  10Main group elements (i.e. group 2) - generally one oxidation state:
  11
  12| elements      | valence config | oxidation state |
  13| ------------- | -------------- | --------------- |
  14| alkali metals | $s^1$          | +1              |
  15| alkali earths | $s^2$          | +2              |
  16| aluminium     | $s^2 p^1$      | +2              |
  17| nitrogen      | $s^2 p^3$      | -3              |
  18| oxygen        | $s^2 p^4$      | -2              |
  19| halogens      | $s^2 p^5$      | -1              |
  20| noble gases   | $s^2,\>s^2p^5$ | n/a             |
  21
  22Transition metals (d shell) may have several oxidation states.
  23
  24Common oxidation numbers:
  25
  26| elements          | common ox. state | exceptions          |
  27| ----------------- | ---------------- | ------------------- |
  28| main group metals | valency          |                     |
  29| hydrogen          | +1               | metal hydrides (-1) |
  30| oxygen            | -2               | ce{H2O2} (-1)       |
  31| halogens          | -1               |                     |
  32
  33
  34### Rules for oxidation states
  35
  36- oxidation states >3 may only exist in compounds
  37- oxidation number of free element is 0
  38- oxidation number of simple ion is the charge of the ion
  39- sum of oxidation numbers in polyatomic ion is the charge of the ion
  40- sum of oxidation numbers of a neutral compound is zero
  41
  42## Electrochemical series
  43
  44- Top is most likely to be reduced
  45- Strongest reductants are bottom right
  46- Strongest oxidants are top left
  47- Strong oxidants have weak conjugate reductants
  48- $E^0$ values are measured relative to ce{H2} / ce{H^+} = 0V
  49
  50## Conjugate redox pairs
  51
  52Oxidant and conjugate *reduced form*  
  53e.g. ce{Cu^2+} / ce{Cu}, $\quad$ ce{Zn^2+} / ce{Zn}
  54
  55Usually one member of pair is used as electrode (except for *inert electrodes*, e.g. platinum)
  56
  57## Electrochemical/galvanic cells
  58
  591. Find two half reactions involved (between electrode and solution)
  602. Higher equation will proceed left to right
  613. Lower equation will proceed right to left
  62
  63emf for each cell is calculated as $E^0(\text{red}) - E^0(\text{ox})$  
  64Then total emf is $\sum_{i=1}^2 \Sigma E^0({i})$
  65
  66For a spontaneous reaction to occur, species on left must be in electrical contact with species on lower right