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