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Chapter 19.1: Oxidation and Reduction

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Chapter 19.1: Oxidation and Reduction

  1. 1. Chapter 19.1
  2. 2. 1. Assign oxidation numbers to reactant and product species. 2. Define oxidation and reduction. 3. Explain what an oxidation-reduction reaction (redox reaction) is.
  3. 3. • The oxidation number assigned to an element in a molecule is based on the distribution of electrons in that molecule. • The rules by which oxidation numbers are assigned are summarized on the next slide. chromium (II) chloride chromium (III) chloride potassium chromate potassium dichromate
  4. 4. • Reactions in which the atoms or ions of an element experience an increase in oxidation state are oxidation processes. • A species whose oxidation number increases is oxidized.
  5. 5. • Reactions in which the oxidation state of an element decreases are reduction processes. • A species that undergoes a decrease in oxidation state is reduced. Aluminum from Aluminum Oxide Tungsten from Tungsten Oxide
  6. 6. • Any chemical process in which elements undergo changes in oxidation number is an oxidation- reduction reaction. • This name is often shortened to redox reaction. • The part of the reaction involving oxidation or reduction alone can be written as a half-reaction.
  7. 7. • Equations for the reaction between nitric acid and copper illustrate the relationship between half- reactions and the overall redox reaction. 2+ +20 Cu Cu + 2e – +5 2 +1 +4 2 +1 + 23 2 22NO + 2 + 4H 2NO + 2H Oe  – – – – – +5 + 2+ 3 2 +20 +4 2Cu + 2NO + 4H Cu + 2NO + 2H O– (oxidation half-reaction) (reduction half-reaction) (redox reaction)
  8. 8. • When hydrogen burns in chlorine, a covalent bond forms from the sharing of two electrons. • The pair of electrons is more strongly attracted to the chlorine atom because of its higher electronegativity. 2 2 0 0 +1 1 H + Cl 2HCl – • Neither atom has totally lost or totally gained any electrons. • Hydrogen has donated a share of its bonding electron to the chlorine but has not completely transferred that electron.

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