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Redox

Redox. Chemistry 2AB. Historically. oxidation was considered as a reaction where a substance reacts with oxygen ie a gain of oxygen Examples are burning or rusting Reduction reactions were associated with loss of oxygen. REDOX stands for REDuction/OXidation.

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Redox

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  1. Redox Chemistry 2AB

  2. Historically • oxidation was considered as a reaction where a substance reacts with oxygen ie a gain of oxygen • Examples are burning or rusting • Reduction reactions were associated with loss of oxygen

  3. REDOX stands for REDuction/OXidation • Oxidation refers to a loss of electrons • Reduction refers to a gain of electrons • As a mnemonic remember LEO says GER or OILRIG

  4. What is oxidation? What is reduction? • oxidation = loss of e– … X X+ + e– • reduction = gain of e– … X + e– X– Q- Is it possible to oxidize a material without reducing something else? A- No. A lost e– is taken up by something else

  5. Oxidising and Reducing agents • An oxidizing agent causes oxidation by being reduced itself • A reducing agent causes reduction by being oxidized itself

  6. Redox reactions • When an oxidation reaction occurs a reduction reaction occurs at the same time. • Oxidation numbers are a way of figuring our whether a particular reaction is a redox reaction or not.

  7. Half equations Ca + Cl2 CaCl2 Redox reactions can be split into half equations: Ca  Ca2+ + 2e– oxidation Cl2 + 2e– 2Cl–reduction Cl2 is the oxidising agent (oxidant) Ca is the reducing agent (reductant)

  8. Oxidation Numbers • Oxidation numbers are a simple way to identify redox reactions. • Notice that oxidation numbers are written as eg +1 rather than 1+ to distinguish them from charges

  9. Learn these rules! 1. Any element, when not combined with atoms of a different element, has an oxidation number of zero. (K, Mn, F2, O2 are 0) 2. Any simple monatomic ion (one atom ion) has an oxidation number equal to its charge (Na+ is +1, O2– is –2) 3. The sum of the oxidation numbers of all of the atoms in a formula must equal the charge written for the formula. (if the oxidation number of O is –2, then in CO32– the oxidation number of C is +4)

  10. 4. In compounds, the oxidation number of Group I metals is +1, Group II is +2, and Group III eg aluminum is +3 5. In ionic compounds, the oxidation number of a nonmetal or polyatomic ion is equal to the charge of its associated ion. (CuCl2, Cl is –1) • O is usually –2 (unless in H2O2 (-1)_or F2O (+2), • H is usually +1 (except in metal hydrides when it is -1)

  11. A reaction between aluminium and bromine

  12. Halogen displacement

  13. Use oxidation numbers to identify redox reactions

  14. Identify oxidising agents and reducing agents

  15. Different oxidations states of Cl in different acids

  16. Some questions

  17. Disproportionation

  18. C3H8O + CrO3 + H2SO4 Cr2(SO4)3 + C3H6O + H2O Balancing reactions

  19. Half equations-for monatomic ions • Identify species being oxidised (or reduced) • Balance the atoms • Balance the charge

  20. There are 2 methods • Oxidation number • Ion electron • I will use the ion-electron method

  21. Steps to follow: • Write down reactant and product along with the ON of the substance being oxidised or reduced. • Balance the no of atoms of the species being oxidisied or reduced • Balance O by adding water • Balance H by adding H+ • Balance electrons • Cancel out anything on both sides of the equation. • Check!

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