2. Redox Reactions

3. Reactants: Zn + I 2 Product: Zn I 2

4. Redox Equations: At the conclusion of our time together, you should be able to: 1.Define redox 2.Figure out oxidation numbers for any element 3.Show the change in oxidation numbers in a reaction

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6. What’s the Point ? Electrical production (batteries, fuel cells) REDOX reactions are important in … Purifying metals (e.g. Al, Na, Li) Producing gases (e.g. Cl 2, O 2, H 2 ) Electroplating metals Protecting metals from corrosion Balancing complex chemical equations Sensors and machines (e.g. pH meter) C 3 H 8 O + CrO 3 + H 2 SO 4  Cr 2 (SO 4 ) 3 + C 3 H 6 O + H 2 O

7. What is Redox? REDOX stands for REDuction/OXidation Oxidation is often thought of as a combination of a substance with oxygen (rusting, burning) Oxidation refers to a loss of electrons Reduction refers to a gain of electrons As a mnemonic remember LEO says GER Loss Electrons = Oxidation Gain Electrons = Reduction

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9. Let’s See How You’re Doing?? Q- What is oxidation? What is reduction? Represent each as a chemical equation. oxidation = loss of e – … X  X + + e – reduction = gain of e – … X + e –  X – Q- Why is 2Na + Cl 2  2NaCl considered a redox reactions? This involves the transfer of electrons. (Na has no charge, the atoms in diatomic molecules have no partial charge. After reaction the atoms have different shares of the electrons because of different EN values)

10. Let’s See How You’re Doing?? Q- Is it possible to oxidize a material without reducing something else? No. A lost e – is taken up by something else.

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12. Determination of Oxidizing and Reducing Agents I. Determine oxidation # for all atoms in both the reactants and products. II. Look at the same atom in reactants and products and see if oxidation # increased or decreased. If oxidation # decreased; substance reduced If oxidation # decreased; substance reduced If oxidation # increased; substance oxidized If oxidation # increased; substance oxidized

13. Determination of Oxidizing and Reducing Agents (continued) Oxidizing Agent: Substance that oxidizes the other substance by accepting electrons. It is reduced in reaction. Oxidizing Agent: Substance that oxidizes the other substance by accepting electrons. It is reduced in reaction. Reducing Agent: Substance that reduces the other substance by donating electrons. It is oxidized in reaction. Reducing Agent: Substance that reduces the other substance by donating electrons. It is oxidized in reaction.

14. Let’s See How You’re Doing?? Q-Define oxidizing agent, reducing agent. An oxidizing agent causes oxidation by being reduced itself A reducing agent causes reduction by being oxidized itself

15. Review of Oxidation Numbers We will see that there is a simple way to keep track of oxidation and reduction We will see that there is a simple way to keep track of oxidation and reduction This is done via “oxidation numbers” This is done via “oxidation numbers” An oxidation number is the charge an atom would have if electrons in its bonds belonged completely to the more electronegative atom An oxidation number is the charge an atom would have if electrons in its bonds belonged completely to the more electronegative atom e.g. in HCl, Cl has a higher EN. Thus, oxidation numbers are Cl = -1, H = +1 e.g. in HCl, Cl has a higher EN. Thus, oxidation numbers are Cl = -1, H = +1 Notice that oxidation numbers are written as +1 vs. 1+ to distinguish them from charges. Notice that oxidation numbers are written as +1 vs. 1+ to distinguish them from charges.

16. 1.Any element, when not combined with atoms of a different element, has an oxidation # of zero. (O in O 2 is zero, Na by itself is zero) 2.Any simple monatomic ion (one-atom ion) has an oxidation number equal to its charge (Na + is +1, O 2– 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 CO 2 the oxidation number of C is +4) Oxidation Numbers Rules

17. 4. In compounds, the oxidation # of IA metals is +1, IIA is +2, IIIA is +3, 13 is +3, Zn & Cd is +2, Ag is +1. 5. In ionic compounds, the oxidation # of a nonmetal or polyatomic ion is equal to the charge of its associated ion. (MgCl 2, Mg is +2, therefore Cl is –1) 6. F is always –1, O is always –2 (unless combined with F), H is usually +1, except when it is bonded to metals in binary compounds. (ex. NaH, H oxidation # is –1 or when it’s in elemental form H 2, oxidation # is 0). Oxidation Number Rules

19. NaIO 3 Na = +1 O = -2 3x(-2) + 1 + ? = 0 I = +5 IF 7 F = -1 7x(-1) + ? = 0 I = +7 Oxidation numbers of all the elements in the following ?

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21. Redox Equations: Let’s see if you can: 1.Define redox 2.Figure out oxidation numbers for any element 3.Show the change in oxidation numbers in a reaction

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23. RuleTotalOx.# +1 6 -2 6 -6+5 3 +1 4 +2 -2 6 -14+12 3 +6 or rule 5 +1 6 +6 -2 6 -4 3 -2 5 +1 4 H N O 3 C2H6OC2H6OK 2 Cr 2 O 7 AgI +1 6 +2 -2 6 -8+5 3 H 2 PO 4 – Let’s Apply the Oxidation Rules

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25. Corrosion – Deterioration of Metals by Electrochemical Process Let’s consider what happened to the iron ribbing of the Statue of Liberty

26. Iron loses e-, therefore is oxidized Oxygen gaines e-, therefore is reduced Iron loses e-, therefore is the reducing agent Oxygen gaines e-, therefore is the oxidizing agent

27. Corrosion – Deterioration of Metals by Electrochemical Process Determine and balance the reaction, determine what is oxidized and what is reduced.

28. Corrosion of Silver Ag + O 2  Ag 2 O 4 Ag + O 2  2 Ag 2 O - Each Ag loses 1e - - Each O gains 2e - Silver = oxidized Oxygen= reduced Silver = reducing agent Oxygen = oxidizing agent

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30. Redox Reactions

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32. Redox Equations: At the conclusion of our time together, you should be able to: 1.Review redox 2.Review oxidation numbers for any element 3.Show the change in oxidation numbers in a reaction and show the reaction

33. What is Redox? REDOX stands for REDuction/OXidation Oxidation is often thought of as a combination of a substance with oxygen (rusting, burning) Oxidation refers to a loss of electrons Reduction refers to a gain of electrons As a mnemonic remember LEO says GER Loss Electrons = Oxidation Gain Electrons = Reduction

34. Let’s See How You’re Doing?? Q- What is oxidation? What is reduction? Represent each as a chemical equation. oxidation = loss of e – … X  X + + e – reduction = gain of e – … X + e –  X – Q- Why is 2Na + Cl 2  2NaCl considered a redox reactions? This involves the transfer of electrons. The oxidation numbers change for 2 elements. Na goes from 0 to +1 Cl goes from 0 to

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36. Let’s See How You’re Doing?? Q- Is it possible to oxidize a material without reducing something else? No. A lost e – is taken up by something else.

37. Redox Reactions Reactants: Zn + I 2 Product: Zn I 2

38. Redox Reactions Reactants: Zn + I 2 Product: Zn I 2 - Each Zn loses 2e - - Each I gains 1e - Zinc= oxidized Iodine= reduced Zinc = reducing agent Iodine = oxidizing agent

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