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Electrochemistry Ch. 17

Electrochemistry Ch. 17. Moving Electrons. What kind of chemical reaction relates to the concept of electricity? Redox Reactions: electrons are moving from atom to another; moving electrons produce electricity Battery : controlled chemical reaction to produce an electrical current

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Electrochemistry Ch. 17

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  1. ElectrochemistryCh. 17

  2. Moving Electrons • What kind of chemical reaction relates to the concept of electricity? Redox Reactions: electrons are moving from atom to another; moving electrons produce electricity • Battery: controlled chemical reaction to produce an electrical current • Electrolysis: using electricity to causes a chemical reaction

  3. Electrolysis • Electrolytic cell- device, when attached to a power source (battery) induces a chemical reaction • Two Electrodes: Cathode- releases electrons, takes in Cations (negatively charged) Anode- takes electrons, takes in Anions (positively charged) • REDCAT??? REDuction at the CAThode Oxidation at the Anode ????

  4. Electrolytic Cell • If the following compound was separated using electrolysis: 2Al2O3  4Al(s) + 3O2(g) • What is oxidized/reduced? • What are the cations/anions? • What elements will move to the cathode/anode? Al; +30, reduced O; -20, oxidized Al+3Cation O-2Anion Al+3Cathode O-2Anode

  5. Using Electrolysis • Removing elements from compounds: 2NaCl(aq)+2H2O(l)Cl2(g)+H2(g)+2NaOH(aq) • Refining Ores- remove pure metal from compounds found in the Earth • Electroplating- cheap and effective why to coat and protect reactive metals • Electrolytic Cleaning- restoring aged materials

  6. Refining Ores • Before refining aluminum was possible, pure aluminum was more rare than gold or sliver • Today it is one of the most widely used metals Bauxite Ore Pure Aluminum • Heat the Bauxite Ore to remove water and impurities. What is a compound with H2O inside it? A Hydrate 2) Al2O3 is heated to about 1000oC 3) Molten Al2O3 goes through electrolysis

  7. Refining Aluminum • In a electrolytic cell with Carbon anodes, oxygen is drawing towards the carbon to produce CO2 • Al ions settle on the bottom of the container making pure liquid aluminum 2Al2O3(s)+3C(s)4Al(l)+3CO2(g) • What is oxidized/reduced? Al; +30, reduced C; 0+4; oxidized

  8. Electroplating • Reactive metals need a protective coating to prevent rusting or tarnishing • Zinc makes a great coat for steel • Metal plating using gold, silver, and copper is also common • Object to be plated cathode • Metal coating anode

  9. Electrolytic Cleaning • Cleaning objects by pulling ions of chemical build up • Antiques coated in salts • Old object cathode • Stainless steel anode • Chlorine and other salt compounds can be removed

  10. Electrochemical Cells • A spontaneous redox reaction that can be used to produce an electrical current • Required: • A metal cathode; site of reduction • A metal anode; site of oxidation • An electrolyte solution; allow transfer of electrons • The type of metal used determines if it is a cathode or an anode • Metal more easily reduced is cathode • Metal more easily oxidized is anode

  11. Potential Difference • The type of metal and the amount used determines the strength of the electrical current • Potential difference- difference between how easily the anode is oxidized and the cathode is reduced • Voltage (Alessandro Volta) • Which produces a larger voltage; a current between Lithium/Zinc or Sodium/Magnesium? • Why is it better to make jewelry out of Gold, Silver, Copper, and Platinum? Lithum/Zinc Not very reactive; wont corrode

  12. Galvanic Cells • Battery (voltaic cell)- controlled spontaneous redox reaction to produce a current • Mg/Cu Galvanic Cell: • What is oxidized/reduced? What is the cathode/anode? • MgSO4 and CuSO4 containers are connected by a salt bridge • Keeps solutions separate but allows ion movement • Mg2+ ions build up at anode; Cu2+ removed at cathode • Salt ions neutralize a build up of charges as the Mg2+/Cu2+ change places Mg: oxidized; becomes the anode Cu: reduced; becomes the cathode

  13. Types of Batteries • Carbon-Zinc Dry Cell • Carbon center (cathode); MnO2 coating • Zinc cover (anode) • Electrolyte gel (NH4Cl-ZnCl2) • Zinc is oxidized; Zn Zn2++2e- • Manganese is reduced; 2MnO2+H2O+2e- Mn2O3+2OH-

  14. Types of Batteries • Lead Storage Battery • Lead (IV) Oxide electrode • Lead electrode • Sulfuric acid electrolyte • Lead (IV) is reduced and Lead is oxidized Pb(metal)Pb2++2e- Pb+4+2e-Pb2+ • Pb2+combines with SO42- ions • Both anode and cathode collect PbSO4 • Reaction reversible

  15. Alternative Batteries • NiMH battery (Nickel + Metal Hydride) • Rechargeable • Use electrolysis to reverse the redox reaction • Lose 1% of their charge a day when even not used • Lithium battery • Holds a more charge • Li is easiest to oxidize (produces a large potential difference) • Li explodes in water

  16. Alternative Batteries • Hydrogen-Oxygen Fuel Cell • Electrodes are inert metals • Produces H2O as by-product • Could be possible alternative to gasoline cars • Hydrogen and Oxygen are very abundant elements on earth • Super Battery? • In 2009 a Lithium super battery was produced using nano-engineering • Releases energy 100 times faster • Could recharge an electric car faster than it takes to pump gas into a gasoline car

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