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Chapter 15 Oxidation and Reduction

Chapter 15 Oxidation and Reduction. 15.2 Oxidation Numbers Learning Goal Assign and use oxidation numbers to identify elements that are oxidized or reduced. Lead oxides, once used in paint, are now banned due to the toxicity of lead. Oxidation and Reduction. An oxidation number

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Chapter 15 Oxidation and Reduction

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  1. Chapter 15 Oxidation and Reduction 15.2 Oxidation Numbers Learning Goal Assign and useoxidation numbers to identifyelements that are oxidized or reduced. Lead oxides, once used in paint, are now banned due to the toxicity of lead.

  2. Oxidation and Reduction An oxidation number • is assigned to each atom in a compound or ion • is negative for the more electronegative atom • helps to identify which elements undergo oxidation and which undergo reduction • keeps track of the loss and gain of electrons

  3. Rules for Assigning Oxidation Numbers

  4. Examples of Using Rules to Assign Oxidation Numbers

  5. Examples of Using Rules to Assign Oxidation Numbers

  6. Examples of Using Rules to Assign Oxidation Numbers

  7. Examples of Using Rules to Assign Oxidation Numbers

  8. Learning Check Assign oxidation numbers to the atoms in each. A. MgCl2 B. CCl4

  9. Solution Assign oxidation numbers to the atoms in each. A. MgCl2 MgCl2 Mg in 2A(2) = +2; +2 −1 Cl in 7A (17) = −1 Check: (+2) +2(−1) = 0 B. CCl4 CCl4 C + 4(−1) = 0 +4 −1 C = +4 Check: (+4) +4(−1) = 0

  10. Learning Check Assign oxidation numbers to the elements in each of the following: A. N2 B. PO43−

  11. Solution Assign oxidation numbers to the elements in each of the following: A. N2 N = 0 0 B. PO43− P + 4(−2) = –3 +5 −2 P = −3 + 8 = +5 Check: (+5) + 4(−2) = −3

  12. Learning Check Determine the oxidation number of each of the following: A. C in CO2 +2 +4 −4 B. Cl in Cl2O7 +2 +7 −14 C. Mn in MnO4− +4 +7 +8

  13. Solution Determine the oxidation number of each of the following: A. C in CO2 +4 B. Cl in Cl2O7 +7 C. Mn in MnO4− +7

  14. Identifying Oxidation, Reduction When the oxidation number for an element • increases, oxidation (loss of e− ) has occurred • decreases, reduction (gain of e− ) has occurred

  15. Identify Oxidation and Reduction Oxidation numbers can be used to identify the elements that are oxidized and the elements that are reduced in a reaction.

  16. Guide to Using Oxidation Numbers

  17. Learning Check Identify the element that is oxidized and the element that is reduced in the following equation: CO2(g) + H2(g)  CO(g) + H2O(g)

  18. Solution Identify the element that is oxidized and the element that is reduced in the following equation: CO2(g) + H2(g)  CO(g) + H2O(g) Step 1 Assign oxidation numbers to each element.

  19. Solution Identify the element that is oxidized and the element that is reduced in the following equation: CO2(g) + H2(g)  CO(g) + H2O(g) Step 2Identify the increase in oxidation number as oxidation; the decrease as reduction.

  20. Oxidizing and Reducing Agents • In an oxidation–reduction reaction, the substance that is oxidized is called the reducing agent because it provides electrons. • The substance that is reduced is called the oxidizing agent because it accepts electrons Zn(s)  Zn2+(aq)+ 2 e− Zn is oxidized; therefore it is the reducing agent. Cl2(g) + 2 e− 2Cl−(aq)Cl2 is reduced; therefore it is the oxidizing agent.

  21. Learning Check Identify the substance that is oxidized, the substance that is reduced, the oxidizing agent, and the reducing agent. 2Cs(s) + F2(g)  2CsF(aq)

  22. Solution Identify the substance that is oxidized, the substance that is reduced, the oxidizing agent, and the reducing agent.

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