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Chemistry SM-1232 Week 10 Lesson 3

Chemistry SM-1232 Week 10 Lesson 3. Dr. Jesse Reich Assistant Professor of Chemistry Massachusetts Maritime Academy Spring 2008. Class Today. No class Friday Tests are graded Quizes are not yet graded. I’ll have them sometime this week.

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Chemistry SM-1232 Week 10 Lesson 3

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  1. Chemistry SM-1232Week 10 Lesson 3 Dr. Jesse Reich Assistant Professor of Chemistry Massachusetts Maritime Academy Spring 2008

  2. Class Today • No class Friday • Tests are graded • Quizes are not yet graded. I’ll have them sometime this week. • Only 1 wiki even started!!! GET ON IT! At least start the page. • Quote • Chapter 16- just two days, today and Wednesday • Quiz on the Wiki on Friday • Start Chapter 18 on Monday, Test next Wednesday

  3. Sea Fever • I must down to the seas again, to the lonely sea and the sky,And all I ask is a tall ship and a star to steer her by,And the wheel's kick and the wind's song and the white sail's shaking,And a grey mist on the sea's face, and a grey dawn breaking.I must down to the seas again, for the call of the running tideIs a wild call and a clear call that may not be denied;And all I ask is a windy day with the white clouds flying,And the flung spray and the blown spume, and the sea-gulls crying.I must down to the seas again, to the vagrant gypsy life,To the gull's way and the whale's way where the wind's like a whetted knife;And all I ask is a merry yarn from a laughing fellow-roverAnd quiet sleep and a sweet dream when the long trick's over.By John Masefield (1878-1967).(English Poet Laureate, 1930-1967.)

  4. Oxidation • 2 H2 + O2 2H2O • 4 Fe(s) + 3O2  2 Fe2O3 • CH4 + O2  CO2 + H2O • Each chemical reacting with oxygen ends up with oxygen in the formula. Since they gain oxygen we call it an oxidation or an oxidizing reaction.

  5. Reduction • 2 H2O  2H2 + O2 • 2 Fe2O3(s)  4Fe + 3O2 • CO2 + H2O  CH4 + 2 O2 • The reaction produces oxygen in each case. When the reaction loses oxygen it’s called a reduction.

  6. Oxydation does not need oxygen • 4 Na + O2 2Na2O • 2 Na + Cl2  2 NaCl • Chemists consider both to be oxidation reactions

  7. A closer look • 4 Na + O2 2Na2O • Each Na is losing an electron • 4Na  4Na+ + 4e- • Oxygen is gaining two electrons • O2 + 4e- 2O2-

  8. similarly • 2 Na + Cl2 2 NaCl • Each Na is losing an electron • 2Na  2Na+ + 2e- • Chlorine is gaining one electrons • Cl2 + 2e- 2Cl-

  9. You try • Mg + Cl2 MgCl2 • 2Ca + O2  CaO

  10. Simpler definition • LeoGer • Aka Leo the Lion goes Ger • Lose electrons = oxidation • Gain Electrons = reduction

  11. Redox reactions happen simultaneously • As an oxidation occurs to lose electrons a reduction is happen to gain electrons. • The substance that is oxidized is called the reducing agent because it causes the reduction of the other substance. • The substance that is reduced is called the oxidizing agent because it causes the oxidation of the other substance.

  12. Labels Applied • 2H2 + O2 2H2O • H2 is the reducing agent because it’s reducing oxygen. • O2 is called the oxidizing agent because it’s oxidizing H2.

  13. You try • Write the reactions and label which is the oxidizing agent and which is the reducing agent. • 2Mg + O2 MgO • Fe + Cl2  FeCl2 • Zn(s) + Fe+2  Zn+2 + Fe(s)

  14. Oxydation State: keeping track of electrons • C + 2S  CS2 • Let’s figure out where the electrons are!

  15. Rules! • 1. Pure elements have an oxydation state of 0 • 2. Any charged ion has an oxydation state equal to its charge • 3. If a compound is neutral the sum of all oxydation states equals 0 • 4. If a compound is charged the sum of all oxydation states equals the charge • 5. Group 1,2,3 will always be +1,+2,+3 • 6. Non metals get oxidation numbers on the next slide.

  16. More Rules: Oxidation numbers • This is list is also in order of precedence! • Fluorine oxidation is always -1 • Hydrogen is +1 • Oxygen is -2 • Group 7 is -1 • Group 6 is -2 • Group 5 is -3

  17. Examples • Br2 • K+ • LiF • CO2 • SO42- • Na2O2

  18. Back to Carbon and Sulfur • C + 2S  CS2 • What are the oxidation states? • What gets oxidized? • What gets reduced? • Which is the oxidizing agent? • Which is the reducing agent?

  19. Balancing Redox Equations • Al(s) + Ag+(s)  Al3(aq)+ + Ag(s) • What are the oxidation numbers of each one of these? • Let’s break this down into the oxidation and the reduction!

  20. Oxidation • Al  Al+3 • What’s the oxidation state of Al? Al+3 • This isn’t balanced! • We’re missing the electrons! • Al  Al+3 + 3e- • Now we are balanced!

  21. Reduction • Ag+  Ag(s) • What’s the oxidation state of Ag(s)? Ag+? • This isn’t balanced! • We’re missing the electrons! • Ag + + e-  Ag(s)

  22. Let’s look at them together • Al(s)  Al+3 + 3e- • 1 e- + Ag+  Ag(s) • How many times must Ag+ be reduced in order for 1 Al(s) be oxidized?

  23. 3 Times! • Al(S)  Al+3 + 3 e- • 3(1e- + Ag+  Ag(s)) • Al(s)  Al+3 + 3e- • 3e- + 3 Ag+  3 Ag(s) • If we add them the electrons can cancel out. • Al(s) + 3 Ag+  3 Ag(s) + Al+3

  24. You Try • Al(s) + Cu+2 Al+3 + Cu(s) • We’re looking to have charge and atom balanced!

  25. Still Time? • I- + Cr2O7-2 Cr3+ + I2(s)

  26. Read all of chapter 16 • Work on your wikis • Work on your homework • Homework due Monday • Take Home Quiz on Friday Too • Review Monday- Start Chapter 18 • Quiz on Wednesday.

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