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17.8

17.8. Commercial Electrolytic Process. Metals: Quick Recap. Characterized by the ability to donate electrons and form ions Good reducing agents Found in ores Ores: ionic compounds with oxide, sulfide, or silicate Noble Metals Gold, silver, platinum More difficult to oxidize.

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17.8

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  1. 17.8 Commercial Electrolytic Process

  2. Metals: Quick Recap • Characterized by the ability to donate electrons and form ions • Good reducing agents • Found in ores • Ores: ionic compounds with oxide, sulfide, or silicate • Noble Metals • Gold, silver, platinum • More difficult to oxidize

  3. Aluminum: Basic Facts • One of the most abundant elements on earth • Active Metal • In nature as “bauxite” • Production of the metal from ore is one of the most difficult • High affinity for oxygen Fun Fact! Napoleon III is known to have served his honored guests with aluminum silverware because that was more expensive then gold or silver at the time.

  4. Hall-Heroult Process • Created by: • Charles M. Hall of the United States • Paul Heoult of France • Invented practical electrolytic process for producing aluminum • Used molten cryolite as a solvent ()

  5. Electrolysis of Aluminum • Not possible • Water is more easily reduced than Al

  6. Melting of aluminum • Melting point of is 2050 °C • Melting point of a mixture of and is 1000 °C • Economically feasible thanks to Hall-Heroult Process

  7. Further Steps • Result is not pure aluminum oxide (alumina) • Includes iron, silicone, titanium, etc • Thus, treated with NaOH (aq)

  8. Reprecipitation of Hydrated Alumina • Aluminate ion, , is separated from the sludge O (s)

  9. Final Steps • Purified alumina is mixed with cryolite and melted. • Reduced to aluminum metal • Reduced in electrolytic cell

  10. Results • Aluminum that is produced is 99.5% pure • Alloyed with zinc of manganese to be useful as a structural material • 5% of electricity in United States, as of 2007, is used in production of aluminum

  11. Electrorefining Metals • The purification of metals is an application of electrolysis • Example • Noble metals, because not oxidized, fall as sludge during reactions • Easily collectable • produces copper 99.5 % pure

  12. Metal Plating • To avoid corrosion, a thin coating of a metal is put on top of another • To create, the metal is put in a tank containing the ions of plating metal and metal plating results

  13. Electrolysis of Sodium Chloride • The melting point of sodium chloride is 800 °C (that’s high) • However, calcium chloride mixed has a melting point of 600 °C (feasible) • So, the two are mixed to lower the melting point of NaCl

  14. Downs Cell • Anode reaction: • Cathode reaction: Na • The liquid sodium is cooled as blocks, however stored in an inert solution because sodium is very reactive.

  15. Electrolysis of Aqueous Sodium Chloride (Brine) • 2nd largest production in United States after aluminum • Water is more easily reduced than sodium ion, so electrolysis less than practical • However, chloride gas produces an anode that can be used • Anode reaction: • Cathode reaction: • Remaining solution contains dissolved NaOH and NaCl

  16. Mercury Cell • Mercury is used as a conductor • Hydrogen gas has a high overvoltage with a mercury electrode, so the sodium ions are reduced • Na metal dissolves in the mercury • Relatively pure solid NaOH recovered

  17. Chlor-Alkai Process • Regenerated mercury pumped back into the electrolysis cell • Due to environmental concerns, this method using mercury has been largely rejected • As of 2007, 75% of the United States Chlor-Alkali production use diaphragm cells instead of mercury

  18. Diaphragm Cell

  19. New Developments • Recently (meaning recently in 2007), a membrane has been used to separate anode and cathode in brine. • Only cations flow through the membrane • Sodium contamination would not occur • Popular in Japan in 2007

  20. The End Thank you for learning about chemistry.

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