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ChemCom 2013

ChemCom 2013. Warm Up: Determine the name and molar mass of the following compounds. NaOH MnO 2 H 2 SO 4. How did you do?. NaOH- 40.00 g/mol, sodium hydroxide MnO 2 - 86.94 g/mol, Manganese (IV) oxide H 2 SO 4 98.09 g/mol, Sulfuric acid

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ChemCom 2013

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  1. ChemCom 2013

  2. Warm Up: Determine the name and molar mass of the following compounds. NaOH MnO2 H2SO4

  3. How did you do? NaOH- 40.00 g/mol, sodium hydroxide MnO2- 86.94 g/mol, Manganese (IV) oxide H2SO4 98.09 g/mol, Sulfuric acid Be sure you go back and review the basics…

  4. ELECTROCHEMISTRY

  5. Electron Transfer Reactions • Electron transfer reactions are oxidation-reduction or redox reactions. • Result in the generation of an electric current (electricity) or be caused by imposing an electric current. • This field of chemistry is often called ELECTROCHEMISTRY.

  6. Terminology for Redox Reactions • OXIDATION—loss of electron(s) by a species; increase in oxidation number; increase in oxygen. • REDUCTION—gain of electron(s); decrease in oxidation number; decrease in oxygen; increase in hydrogen. • OXIDIZING AGENT—electron acceptor; species is reduced. • REDUCING AGENT—electron donor; species is oxidized.

  7. You can’t have one… without the other! • Reduction (gaining electrons) can’t happen without an oxidation to provide the electrons. • You can’t have 2 oxidations or 2 reductions in the same equation. Reduction has to occur at the cost of oxidation LEO the lion says GER! GER!

  8. Another way to remember • OIL RIG

  9. OXIDATION-REDUCTIONREACTIONS Direct Redox Reaction Oxidizing and reducing agents in direct contact. Cu(s) + 2 Ag+(aq) ---> Cu2+(aq) + 2 Ag(s)

  10. OXIDATION-REDUCTION REACTIONS Indirect Redox Reaction A battery functions by transferring electrons through an external wire from the reducing agent to the oxidizing agent.

  11. Batteries • An apparatus that allows a redox reaction to occur by transferring electrons through an external connector. • Product favored reaction voltaic or galvanic cellresults in electric current • Reactant favored reaction electrolytic cell electric current used to cause chemical change. Batteries are voltaic cells

  12. Warm Up- Write the formulas • Calcium hydroxide • Carbon monoxide • Iron (III) chloride • Copper (II) nitrate • Sulfur tetroxide

  13. Basic Concepts of Electrochemical Cells Anode Cathode

  14. Direct Redox Reaction • Zn is oxidized and is the reducing agent Zn(s) ---> Zn2+(aq) + 2e- • Cu2+ is reduced and is the oxidizing agentCu2+(aq) + 2e- ---> Cu(s) With time, Cu plates out onto Zn metal strip, and Zn strip “disappears.” Corrodes away

  15. CHEMICAL CHANGE --->ELECTRIC CURRENT • To obtain a useful current, we separate the oxidizing and reducing agents so that electron transferoccurs thru an external wire. This is accomplished in a GALVANIC or VOLTAIC cell. A group of such cells is called a battery. http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/galvan5.swf

  16. Zn --> Zn2+ + 2e- Cu2+ + 2e- --> Cu Oxidation Anode Negative Reduction Cathode Positive •Electrons travel thru external wire. • Salt bridge allows anions and cations to move between electrode compartments. <--Anions Cations--> RED CAT

  17. Terms Used for Voltaic Cells

  18. OK… that was a lot… Let’s take a little break and do a cool lab

  19. Do the lab on a separate piece of paper… be sure I get the class set of instructions back! • Write the title: Striking it Rich • Write the purpose • Make a materials list as you do the lab • Draw the table that is on the bottom of the page and fill it in as you do the lab. • Answer all the questions on the back of the page… you do NOT need to write a conclucing paragraph!

  20. The Procedure • Clean 3 pennies using the HCl on the demo desk. • Get 4g of granular zinc. • Get 25mL of Zinc Chloride solution • Put the zinc and ZnCl2 in the 100ml beaker. • Put 2 of the 3 pennies in the beaker and place it on the hotplate. • Let the pennies react until they turn a different color. • Carefully wave one of your coated pennies over a flame.

  21. Warm Up (10 minutes) Make sure that your lab is complete… Answer all the questions on the back! Debrief the lab… Collect….

  22. Science Choices

  23. Another Lab…Yea!

  24. Warm Up Write and complete the following sentences with these words. Gains, loses, anode, cathode, red, black. • Oxidation is when a metal __________ electrons, it takes place at the ________ which is ___________ in color. • Reduction is when a metal __________ electrons, it takes place at the ________ which is ___________ in color.

  25. Finish the lab Turn it in!

  26. Have you ever wondered about the voltage on various batteries? 1.7 Volts 12.6 Volts

  27. CELL POTENTIAL, E • For Zn/Cu cell, potential is +1.10 V at 25 ˚C and when [Zn2+] and [Cu2+] = 1.0 M. • This is the STANDARD CELL POTENTIAL, Eo • a quantitative measure of the tendency of reactants to proceed to products when all are in their standard states at 25 ˚C.

  28. Calculating Cell Voltage • Balanced half-reactions can be added together to get overall, balanced equation. Zn(s) ---> Zn2+(aq) + 2e- Cu2+(aq) + 2e- ---> Cu(s) -------------------------------------------- Cu2+(aq) + Zn(s) ---> Zn2+(aq) + Cu(s) If we know Eo for each half-reaction, we could get Eo for net reaction.

  29. + Zn/Cu Electrochemical Cell Zn(s) ---> Zn2+(aq) + 2e- Eo = +0.76 V Cu2+(aq) + 2e- ---> Cu(s) Eo = +0.34 V ---------------------------------------------------- Cu2+(aq) + Zn(s) ---> Zn2+(aq) + Cu(s) Eo = +1.10 V Anode, negative, source of electrons Cathode, positive, sink for electrons

  30. Lead Storage Battery Anode (-) Eo = +0.36 V Pb + HSO4- ---> PbSO4 + H+ + 2e- Cathode (+) Eo = +1.68 V PbO2 + HSO4- + 3 H+ + 2e- ---> PbSO4 + 2 H2O

  31. Charging a Battery When you charge a battery, you are forcing the electrons backwards (from the + to the -). To do this, you will need a higher voltage backwards than forwards. This is why the ammeter in your car often goes slightly higher while your battery is charging, and then returns to normal. In your car, the battery charger is called an alternator. If you have a dead battery, it could be the battery needs to be replaced OR the alternator is not charging the battery properly.

  32. Dry Cell Battery Anode (-) Zn ---> Zn2+ + 2e- Cathode (+) 2 NH4+ + 2e- --> 2 NH3 + H2

  33. Alkaline Battery Nearly same reactions as in common dry cell, but under basic conditions. Anode (-): Zn + 2 OH- --> ZnO + H2O + 2e- Cathode (+): 2 MnO2 + H2O + 2e- --> Mn2O3 + 2 OH-

  34. Mercury Battery

  35. Mercury Battery Anode: Zn is reducing agent under basic conditions Cathode: HgO + H2O + 2e- ---> Hg + 2 OH-

  36. Ni-Cad Battery Anode (-) Cd + 2 OH- ---> Cd(OH)2 + 2e- Cathode (+) NiO(OH) + H2O + e- ---> Ni(OH)2 + OH-

  37. Ni-Cad Battery

  38. H2 as a Fuel Cars can use electricity generated by H2/O2 fuel cells. H2 carried in tanks or generated from hydrocarbons

  39. Warm Up • Draw a voltaic cell that would have Magnesium and Iron metal and Mg2+ and Fe2+ ions. • Using the table on p.453, determine which metal would be oxidized and which would be reduced. • Label the anode and the cathode. • Draw an arrow indicating the flow of electrons. • Write the half reactions. • How would we determine the voltage??

  40. Electrolysis • describes what happens in an electrolytic cell • means to use electricity to make chemicals. • Many elements are “made” by electrolysis • Pb Al Zn Na K Li H2 Cl2 F2 I2 O2

  41. Aluminum Production by Electrolysis Name of the Ore imported from (Guinea and Brazil) Bauxite Al2O3.3H2O Heating drives off the water Al2O3.3H2O + Heat → Al2O3 +3H2O Melting point of Bauxite is 2045 0C This istoohot! Cryolite is added Lowers the melting point to 1000 0C

  42. Reduction of water You cannot reduce Aluminum in water! It must be molten!

  43. Liquid Al floats to the top and is removed DC Power - + Oxygen gas C C - Reduction Cathode Al3+ + 3e-→ Al(s) + Oxidation Anode O2-→ 1/2O2(g) + 2e- Al3+ O2- Al2O3(l) Cation Cathode Reduction Anion Anode Oxidation

  44. Electroplating Auplatinga Cu penny Electroplatingis the process of reducing a metalon to the surface of another Electrolyte: Must contain the ion of the metal that plates Cathode: The metalto be covered with a new metal Anode:Metal to be plated on top the other metal DC Power - + e- - Reduction Cathode Au+ + e-→ Au(s) Au + Oxidation Anode Au(s) → Au+ + 1e- Au+ CN- Cu Cu

  45. +ve -ve stainless steel or Au AuCN

  46. Au plated

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