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Chemistry 20.2

Chemistry 20.2. 20.2. Oxidation Numbers.

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Chemistry 20.2

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  1. Chemistry 20.2

  2. 20.2 Oxidation Numbers • When aluminum or magnesium powder in fireworks are heated to high temperatures in the explosion, they burn with an intense white light. As elements burn, their oxidation numbers change. You will learn about how oxidation and reduction are defined in terms of a change in oxidation number.

  3. 20.2 Assigning Oxidation Numbers • Assigning Oxidation Numbers • What is the general rule for assigning oxidation numbers?

  4. 20.2 Assigning Oxidation Numbers • An oxidation number is a positive or negative number assigned to an atom to indicate its degree of oxidation or reduction.

  5. 20.2 Assigning Oxidation Numbers • As a general rule, a bonded atom’s oxidation number is the charge that it would have if the electrons in the bond were assigned to the atom of the more electronegative element.

  6. 20.2 Assigning Oxidation Numbers • The oxidation number of any element in the free or uncombined state is zero.

  7. 20.2 Assigning Oxidation Numbers

  8. 20.2 Assigning Oxidation Numbers • Oxidation numbers are often written above the chemical symbols in a formula.

  9. 20.2 Assigning Oxidation Numbers K2CrO4 Cr oxidation number = +6 Cr2O3 Cr oxidation number = +3

  10. for Conceptual Problem 20.2 Problem Solving 20.9 Solve Problem 9 with the help of an interactive guided tutorial.

  11. 20.2 Oxidation-Number Changes in Chemical Reactions • Oxidation-Number Changes in Chemical Reactions • How are oxidation and reduction defined in terms of a change in oxidation number?

  12. 20.2 Oxidation-Number Changes in Chemical Reactions • An increase in the oxidation number of an atom or ion indicates oxidation. A decrease in the oxidation number of an atom or ion indicates reduction.

  13. 20.2 Oxidation-Number Changes in Chemical Reactions

  14. 20.2 Oxidation-Number Changes in Chemical Reactions • When an iron nail is placed in a copper(II) sulfate solution, the iron reduces Cu2+ ions in solution and is simultaneously oxidized to Fe2+ The iron becomes coated with metallic copper.

  15. for Conceptual Problem 20.3 Problem Solving 20.11 Solve Problem 11 with the help of an interactive guided tutorial.

  16. 20.2 Section Quiz. • 20.2.

  17. 20.2 Section Quiz. • 1. Which of the following oxidation numbers is INCORRECT? • ClO3– ; Cl +5, O –2 • SO32– ; S +4, O –2 • H2O2; H +1, O –1 • Ca(ClO)2; Ca +2, Cl +2, O –2

  18. 20.2 Section Quiz. • 2. What is the oxidation number of Co in CoCl63–? • –3 • –6 • +9 • +3

  19. 20.2 Section Quiz. • 3. In the reaction PbO2(aq) + 4HBr(aq)  PbBr2(aq) + Br2(l) + 2H2O(l) which element has the greatest change in oxidation number? • hydrogen • oxygen • bromine • lead

  20. END OF SHOW

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