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REDOX

REDOX. Oxidation and Reduction Chapters 20 and 21. What is redox ? Examples. Corrosion (Rusting) Spoiling of Food Voltaic Cells Batteries Electroplating. What is redox ? Examples. Oxidation. Reduction. Complete loss of electrons (ionic)

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REDOX

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  1. REDOX Oxidation and Reduction Chapters 20 and 21

  2. What is redox? Examples • Corrosion (Rusting) • Spoiling of Food • Voltaic Cells • Batteries • Electroplating

  3. What is redox? Examples Oxidation Reduction • Complete loss of electrons (ionic) • Shift of electrons away from an atom in a covalent bond • Gain oxygen • Loss of hydrogen • Increase in oxidation number • Complete gain of electrons (ionic) • Shift of electrons toward an atom in a covalent bond • Loss of oxygen • Gain of hydrogen • Decrease in oxidation number

  4. What is a redox reaction? • Take the following reaction, as an example. 2 Mg + O2MgO 2 What type of reaction is this? Synthesis But we can also define this reaction as a redox reaction.

  5. What is a redox reaction? • Oxidation • When electrons are lost in a chemical reaction • Reduction • When electrons are gained in a chemical reaction • LEO the Lion says “GER” • GER – Gaining Electrons Recuction • LEO – Losing Electrons Oxidation

  6. What is a redox reaction? • In our reaction: • Magnesium is being oxidized (losing electrons) • Oxygen is being reduced (gaining electrons) • The substance being reduced, is causing oxidation, and therefore, is the oxidizing agent • The substance being oxidized, is causing reduction, and therefore, is the reducing agent

  7. Oxidation Numbers • Oxidation Numbers • Apparent numbers (charge) assigned to an atom of an element • Show whether the element is gaining or losing electrons in a reaction • Sometimes the oxidation number is not the same as the oxidation state (ex. Central atoms of a compound or molecule, that has a lower electronegativity than the surrounding atoms)

  8. Oxidation Numbers • Rules for assigning oxidation numbers • The oxidation number for an atom in its uncombined or elemental form is 0. • Ex. Na(s) = 0 Cl2(g) = 0 • The oxidation number for a monoatomic ion is equal to the charge of the ion in its ionic form. • Ex. Na+1 = +1 Cl-1 = -1

  9. Oxidation Numbers • Hydrogen is +1, except when it is bonded to a metal, to form a hydride. Then it is -1. • Oxygen is usually -2, unless it is bonded to a more electonegative atom, like fluorine, or in the form of a peroxide (H2O2) • The sum of the oxidation numbers in a neutral compound or molecule, must be equal to 0. The sum of the oxidation numbers for a polyatomic ion, must be equal to the charge on the ion. • Binary compounds of non-metals, the more electronegative atom gets the negative number.

  10. Changes to oxidation numbers in Chemical Reactions • An increase in the oxidation number indicates oxidation (becoming more +) • A decrease in the oxidation number indicates reduction (becoming more -) • Which type of reaction (synthesis, decompostion, single displacement, double displacement) is not a redox reaction? • Examples

  11. Practice • Page 634 1 – 2 • Page 638 3, 6, 7. a, c, e • Page 641 9, 10 • Page 643 15, 16

  12. Balancing – Using REDOX • Identifying the reaction as a REDOX Reaction is the first step • If the oxidation numbers change, then it is a redox reaction. • Example • There are two ways to balance reactions • Using Oxidation Number changes • Using Half Reactions

  13. Practice • Page 649 19 • Page 654 25 (but use the half reaction method) • Page 661

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