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Electrochemistry

Electrochemistry. Chapter 12. Electrochemistry. Section 1. What happens when zinc is added to hydrochloric acid?. What happens when zinc is added to hydrochloric acid? Zn + 2HCl  ZnCl 2 + H 2 What was the test for hydrogen gas?. What happens when zinc is added to hydrochloric acid?

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Electrochemistry

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  1. Electrochemistry Chapter 12

  2. Electrochemistry Section 1

  3. What happens when zinc is added to hydrochloric acid?

  4. What happens when zinc is added to hydrochloric acid? Zn + 2HCl  ZnCl2 + H2 What was the test for hydrogen gas?

  5. What happens when zinc is added to hydrochloric acid? Zn + 2HCl  ZnCl2 + H2 We can do better than this!

  6. What happens when zinc is added to hydrochloric acid? Zn + 2HCl  ZnCl2 + H2 We can do better than this! Zn + 2H+ Zn2+ + H2

  7. Zn + 2H+ Zn2+ + H2 What is being reduced? What is being oxidized?

  8. Zn + 2H+ Zn2+ + H2 Let’s split the reaction into two parts (called half reactions), the oxidation reaction and the reduction reaction:

  9. Zn + 2H+ Zn2+ + H2 Let’s split the reaction into two parts (called half reactions), the oxidation reaction and the reduction reaction: Zn  Zn2+ + 2e- 2H+ + 2e-  H2

  10. Zn  Zn2+ + 2e- 2H+ + 2e-  H2 What do you see now that we have never shown before?

  11. Zn  Zn2+ + 2e- 2H+ + 2e-  H2 What do you see now that we have never shown before? A properly balanced reaction has the same amount of electrons lost in the oxidation half reaction as is gained in the reduction half reaction.

  12. Let’s separate these half reactions into separate beakers. • Zn  Zn2+ + 2e- • 2H+ + 2e-  H2

  13. Let’s stick the two ends of a wire in. • Zn  Zn2+ + 2e- • 2H+ + 2e-  H2

  14. What will be traveling through the wire? • Zn  Zn2+ + 2e- • 2H+ + 2e-  H2

  15. What will be traveling through the wire? e- e- e- e- • Zn  Zn2+ + 2e- • 2H+ + 2e-  H2

  16. What if we hooked the wire to something, like an iPod? Now we have a battery! e- e- e- e- • Zn  Zn2+ + 2e- • 2H+ + 2e-  H2

  17. What if we hooked the wire to something, like an iPod? Now we have a battery! This situation makes an electrochemical cell called a voltaic cell or galvanic cell. e- e- e- e- • Zn  Zn2+ + 2e- • 2H+ + 2e-  H2

  18. A voltaic (or galvanic) cell is a combination of an oxidation and reduction reaction that spontaneously (thermodynamically favorable) produces an electric current (electrons).

  19. There are some basic things necessary to build a voltaic cell:

  20. There are some basic things necessary to build a voltaic cell: • two electrodes – one is oxidized and called the anode, one is reduced and called the cathode

  21. There are some basic things necessary to build a voltaic cell: • two electrodes – one is oxidized and called the anode, one is reduced and called the cathode • two ionic solutions – the ions should match the electrodes, and be soluble salts

  22. There are some basic things necessary to build a voltaic cell: • two electrodes – one is oxidized and called the anode, one is reduced and called the cathode • two ionic solutions – the ions should match the electrodes, and be soluble salts • a wire to connect the electrodes, typically with a voltmeter to measure the voltage (electron flow)

  23. There are some basic things necessary to build a voltaic cell: • two electrodes – one is oxidized and called the anode, one is reduced and called the cathode • two ionic solutions – the ions should match the electrodes, and be soluble salts • a wire to connect the electrodes, typically with a voltmeter to measure the voltage (electron flow) • a salt bridge – to balance charges so the reaction can continue as long as possible

  24. At this time fill out the first page of our foldable. Be sure to show the loss of mass of the anode and gain in mass of the cathode.

  25. Consider making a voltaic cell from some copper, silver, copper(II) nitrate, and silver nitrate.

  26. Consider making a voltaic cell from some copper, silver, copper(II) nitrate, and silver nitrate. What is the overall spontaneous (thermodynamically favorable) reaction? {Hint: use the shortcut with the standard reduction table.} Don’t forget to balance the electrons!

  27. The Shortcut: using the SRP Table:

  28. The Shortcut: using the SRP Table: 1 - find the elements, not ions, and circle

  29. The Shortcut: using the SRP Table: 1 - find the elements, not ions, and circle

  30. The Shortcut: using the SRP Table: 1 - find the elements, not ions, and circle Why pick copper(II) and not copper(I)?

  31. The Shortcut: using the SRP Table: 2 - draw crossing upward arrows

  32. The Shortcut: using the SRP Table: 2 - draw crossing upward arrows

  33. The Shortcut: using the SRP Table: 3 - things on arrow pointing left are reactants

  34. The Shortcut: using the SRP Table: 3 - things on arrow pointing left are reactants Reactants

  35. The Shortcut: using the SRP Table: 4 - things on arrow pointing left are reactants Reactants

  36. The Shortcut: using the SRP Table: 4 - things on arrow pointing right are products Products Reactants

  37. Cu + Ag+ + e-  Cu2+ + 2e- + Ag NOT BALANCED! Products Reactants

  38. Cu + Ag+ + e-  Cu2+ + 2e- + Ag NOT BALANCED! e- must equal e- gained 2 2 2 Products Reactants

  39. Cu + 2Ag+ + 2e-  Cu2+ + 2e- + 2Ag Now it is balanced, but not reduced! 2 2 2 Products Reactants

  40. Cu + 2Ag+  Cu2+ + 2Ag If you do it right, the electrons will ALWAYS cancel out. This is a great way to check your work.

  41. Cu + 2Ag+  Cu2+ + 2Ag If you do it right, the electrons will ALWAYS cancel out. This is a great way to check your work. What are the oxidation and reduction half reactions?

  42. Cu + 2Ag+  Cu2+ + 2Ag If you do it right, the electrons will ALWAYS cancel out. This is a great way to check your work. What are the oxidation and reduction half reactions? red: Ag+ + e-  Ag

  43. Cu + 2Ag+  Cu2+ + 2Ag If you do it right, the electrons will ALWAYS cancel out. This is a great way to check your work. What are the oxidation and reduction half reactions? red: Ag+ + e-  Ag ox: Cu  Cu2+ + 2e-

  44. What is the cell potential? Note: voltage is an intensive property so does not get multiplied. red: Ag+ + e-  Ag 0.80 V - ox: Cu  Cu2+ + 2e- -0.34 V

  45. What is the cell potential? Note: voltage is an intensive property so does not get multiplied. red: Ag+ + e-  Ag 0.80 V - ox: Cu  Cu2+ + 2e- -0.34 V Where did these numbers come from?

  46. What is the cell potential? Note: voltage is an intensive property so does not get multiplied. red: Ag+ + e-  Ag 0.80 V - ox: Cu  Cu2+ + 2e- -0.34 V 0.46 V

  47. At this time fill in the second page of our foldable. Use potassium nitrate in the salt bridge. Be sure to show the loss of mass of the anode and gain in mass of the cathode.

  48. At this time fill in the final page of our foldable, and assemble.

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