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Redox Intro

Redox Intro. What we know…. Oxidation states are the charges of ions Ions have gained or lost electrons Loosing electrons will make it a positive charge Gaining electrons will make it a negative charge A neutral compound has equal numbers of positive and negative ions

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Redox Intro

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  1. Redox Intro

  2. What we know… • Oxidation states are the charges of ions • Ions have gained or lost electrons • Loosing electrons will make it a positive charge • Gaining electrons will make it a negative charge • A neutral compound has equal numbers of positive and negative ions • Matter and particles can’t just disappear • Law of conservation of mass

  3. Compounds Neutral Compound: no charge NaCl 1+ 1- In order for a compound to be neutral, it must have equal numbers of positive and negative charges

  4. Determining Oxidation State • Some elements only have one oxidation state possible when they form an ion: • Na1+ • Be2+ • B3+ • Other elements have multiple possibilities: • Cl1+, Cl3+, Cl5+, Cl7+, Cl1-

  5. Determining Oxidation State • Use elements that can’t change to figure out the charge on elements that have choices. 10+ 10- 5+ 2- Br2O5

  6. What is the oxidation state of Iron (Fe) in FeF2? • 1+ • 2+ • 3+ • 4+

  7. What is the oxidation state of nitrogen (N) in N2S3? • +1 • +2 • +3 • +4 • +5

  8. Oxidation States • On its own, an element has an oxidation state of 0 • Protons equals the number of electrons 1- 1- 0 1+ 0 1+ Na + HCl H2 + NaCl

  9. Redox Reactions • In the process of a chemical reaction, the oxidation state of an element can change. 3+ 2- 2+ 2- 0 3+ 2+ Fe2O3 FeO + O2 Fe2O3 FeO + O2 e1- +

  10. Half Reactions • Gain Electron: Reduction e1- + Fe3+ Fe2+ • Lose Electron: Oxidation N2+ N3+ + e1- LEO says GER

  11. LEO says GER • If the oxidation state becomes more positive, the ion has lost electrons (oxidized) • If the oxidation state becomes more negative, the ion has gained electrons (reduced) 0 1+ Li  Li + e1- Lose Electron Oxidation

  12. Is the following half reaction showing reduction or oxidation? Fe2+ Fe3+ + e1- • Oxidation • Reduction

  13. Is the following half reaction showing reduction or oxidation? Fe0 Fe2+ + 2e1- • Oxidation • Reduction

  14. Is the following half reaction showing reduction or oxidation? e1- + N1- N2- • Oxidation • Reduction

  15. Which of the following elements will undergo reduction? • Sodium • Barium • Aluminum • Nitrogen

  16. Which of the following elements will undergo oxidation to form an ion? • Potassium • Phosphorus • Bromine • Argon

  17. Writing Half Reactions • Half reactions show the gain or loss of electrons in a chemical reaction. • They only show one element either gaining or losing electrons -2 0 2H2 + O2 2H2O 2H2 + O2 2H2O 4e-1 +

  18. Writing Half Reations 2KCl  2K + Cl2

  19. Writing Half Reactions Zn + 2HCl  H2 + ZnCl2

  20. Redox Reactions:Voltaic Cells

  21. What we know… • Atoms can gain or lose electrons to form ions • LEO says GER: Lose Electron oxidation Gain Electron Reduction • Electrons are transferred between ions

  22. Voltaic Cell • Voltaic Cells harness the transfer of electrons in redox reactions to help power electronic devises

  23. Voltaic Cells • By separating the two ions in a reaction, we can force the electrons to pass through a wire and to do work for us. Zn Cu e- e- e- e-

  24. Voltaic Cell

  25. Voltaic Cell Red Cat An Ox Reduction happens at the cathode Oxidation happens at the anode

  26. Salt Bridge In order to keep the system electrically balanced, you have to have a way to balance the charges The salt bridge allows ions to travel between half-cells.

  27. Voltaic Cell Electrons travel from the anode to the cathode.

  28. Anode and Cathode • Anode: where oxidation happens • Cathode: where reduction happens • The most reactive metal will undergo oxidation and lose its electrons

  29. Electrolytic Cell • If a battery is put into the loop, it can drive the system backwards. • Electrons flow towards the anode and reduction occurs at the anode.

  30. If copper and gold are used as electrodes, copper will be the … • Cathode • Anode • Salt Bridge • Solution

  31. The purpose of a salt bridge is to… • Allow the passage of electrons • Allow the passage of water • Allow the passage of ions • Prevent the passage of electricity

  32. A voltaic cell differs from a electrolytic cell in that it… • Does not involve oxidation • Does not use a battery • Does not use a salt bridge • Does not generate electricity

  33. Oxidation occurs at the… • Cathode • Salt Bridge • Solution • Anode

  34. Which of the following ions undergoes reduction? • Li  Li1+ • Cu2+  Cu1+ • Mg1+  Mg2+ • Zn  Zn2+

  35. What is Electricity?

  36. What we know… • Electrons are negatively charged particles whose configuration determines the chemical properties of elements • When an atom gains an electron it becomes negativelycharged. When an atom loses an electron, it becomes positivelycharged. • In REDOX reactions, electrons from one element are transferred to another element

  37. Electricity • Electricity is the movement of electrons • We power machines and electronics by harnessing the power of moving electrons • Moving electrons generate a magnetic field by which we can spin an axle.

  38. Design Challenge • If we wanted to design an electric car, we would have to develop a way to generate electrons for a motor. • What are the basics to batteries?

  39. What do we know about batteries?

  40. Batteries: Redox Reactions • We know that redox reactions involve the transfer of electrons between elements Two electrons are transferred between iron and sulfur. This does not produce usable electricity as it is instantaneous. Fe2+ Fe S S2-

  41. Batteries: Redox Reactions • We need to separate the two elements so that the electrons transferred can be diverted temporarily. Fe2+ Fe S2- S e1- e1-

  42. Batteries: Voltaic Cells • Electrons flow from the negative electrode to the positive electrode. • On one end of the battery are elements that want to gain electrons and on the other are elements that want to lose electrons. e-1

  43. Batteries: Voltaic Cells • In every battery there are at least two cells of chemicals.

  44. Batteries: Voltaic Cells • The elements that lose electrons undergo oxidation • The elements that gainelectronsundergo reduction Oxidation Reduction

  45. Parts of a Voltaic Cell Wire Wire Salt Bridge Electrode Electrode Salt Solution Salt Solution

  46. e1- e1- Parts of a Voltaic Cell Electrodes: The place where electrons are gained or lost (reduction or oxidation) A copper ion gains two electrons and becomes solid copper metal. Cu2+

  47. Parts of a Voltaic Cell Salt Bridge: Allows for the two salt solutions to stay electrically balanced (neutral), Allows IONS to flow through Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+

  48. Parts of a Voltaic Cell Wire: Allows the electrons to flow from the ANODE to the CATHODE, flow from the negative to the positive electrodes e1- e1- e1- e1-

  49. Parts of a Voltaic Cell Salt Solution: Provides ions for the reduction and oxidation process, provides ions for maintaining electrical neutrality of the cells A copper electrode typically sits in a solution of copper ions. Cu Cu2+ Cu2+ Cu2+ Cu2+ Cu2+

  50. Predicting Electron Flow • How do we figure out if an electrode will gain or lose electrons? • The more reactive element will lose electrons (be oxidized) based on Table J. An Ox Oxidation occurs at the ANODE

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