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23.3 Electrolytic cells
Electrolytic Cells <ul><li>An electrochemical cell that uses electrical energy to cause a chemical reaction ( reverse of a...
Comparing Voltaic and Electrolytic Cells
Comparing Electrolytic & Voltaic Cells <ul><li>In both, electrons flow from anode to cathode </li></ul><ul><li>In both, re...
Comparing Electrolytic & Voltaic Cells <ul><li>In an  electrolytic cell the anode is +,  in a voltaic remember it is  – </...
Electrolysis of Water <ul><li>Splitting of water using electricity- this is done by an electrolytic cell </li></ul><ul><li...
Electrolysis of Water <ul><li>At Cathode  ( - electrode) </li></ul><ul><li>Reduction: 2H 2 O (l)  + 2e -  -----H 2(g)  + 2...
Electrolysis of Water <ul><li>Overall net reaction: </li></ul><ul><li>2H 2 O (l)  electrolysis  2H 2(g)  + O 2(g) </li></u...
Electrolysis of Brine <ul><li>Brine is a concentrated aqueous solution of salt </li></ul><ul><li>Start with NaCl and H 2 O...
Electrolysis of Brine <ul><li>At Anode  (+ electrode) </li></ul><ul><li>Oxidation: 2Cl - (aq)  ------Cl 2(g) +2e - </li></...
Electrolysis of Molten Sodium Chloride <ul><li>Sodium is used in vapor lamps and as a coolant in some nuclear reactors </l...
Electrolysis of Molten Sodium Chloride <ul><li>At Anode  (+ electrode) </li></ul><ul><li>2Cl - (l)  ------Cl 2(g)  + 2e - ...
Electroplating <ul><li>This is the deposition of a thin, very thin ( 10 -5cm ) layer of metal on an object in an electroly...
Electroplating <ul><li>Example: to plate silver on an object </li></ul><ul><li>Make Ag the anode and the object the cathod...
Electroplating <ul><li>Makes things resist corrosion, shiny, more appealing also can be used to make metal molds ( DVD’s o...
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  1. 1. 23.3 Electrolytic cells
  2. 2. Electrolytic Cells <ul><li>An electrochemical cell that uses electrical energy to cause a chemical reaction ( reverse of a voltaic cell) </li></ul><ul><li>Uses energy to drive a non-spontaneous redox reaction </li></ul>
  3. 3. Comparing Voltaic and Electrolytic Cells
  4. 4. Comparing Electrolytic & Voltaic Cells <ul><li>In both, electrons flow from anode to cathode </li></ul><ul><li>In both, reduction occurs at the cathode; oxidation occurs at the anode </li></ul><ul><li>In voltaic cell- reaction is spontaneous; in electrolytic it is non-spontaneous- the electrons are pushed by an outside source ( electricity) </li></ul>
  5. 5. Comparing Electrolytic & Voltaic Cells <ul><li>In an electrolytic cell the anode is +, in a voltaic remember it is – </li></ul><ul><li>In an electrolytic cell the cathode is -, in a voltaic is is + </li></ul>
  6. 6. Electrolysis of Water <ul><li>Splitting of water using electricity- this is done by an electrolytic cell </li></ul><ul><li>Need an electrolyte in water- complete the circuit- usually it is sulfuric acid or sodium hydroxide </li></ul><ul><li>The products are hydrogen gas ( at cathode) and oxygen ( at anode) </li></ul>
  7. 7. Electrolysis of Water <ul><li>At Cathode ( - electrode) </li></ul><ul><li>Reduction: 2H 2 O (l) + 2e - -----H 2(g) + 2OH - (aq) </li></ul><ul><li>Notice- the solution around the cathode will become basic </li></ul><ul><li>At Anode (+ electrode) </li></ul><ul><li>Oxidation: 2H 2 O (l) -----O 2(g) + 4H + (aq) +4e - </li></ul><ul><li>Notice- the solution around the anode will become acidic </li></ul>
  8. 8. Electrolysis of Water <ul><li>Overall net reaction: </li></ul><ul><li>2H 2 O (l) electrolysis 2H 2(g) + O 2(g) </li></ul><ul><li>Extra H + and OH - ions combine to reform water and so are not included I nt ehfinal equation </li></ul>
  9. 9. Electrolysis of Brine <ul><li>Brine is a concentrated aqueous solution of salt </li></ul><ul><li>Start with NaCl and H 2 O </li></ul><ul><li>At Cathode (- electrode) </li></ul><ul><li>reduction: 2H 2 O (l) ------H 2(g) +2OH - (aq) </li></ul><ul><li>Notice: H gets reduced, not Na because water is more easily reduced- the Na becomes a spectator ion which will combine with another spectator ion OH - </li></ul>
  10. 10. Electrolysis of Brine <ul><li>At Anode (+ electrode) </li></ul><ul><li>Oxidation: 2Cl - (aq) ------Cl 2(g) +2e - </li></ul><ul><li>Overall Reaction: </li></ul><ul><li>2NaCl (aq) + 2H 2 O (l) -----Cl 2(g) + H 2 (g) +2NaOH (aq) </li></ul><ul><li>The chlorine is collected and used as disinfectants </li></ul><ul><li>Hydrogen can be collected, and NaOH can also be recovered and used </li></ul>
  11. 11. Electrolysis of Molten Sodium Chloride <ul><li>Sodium is used in vapor lamps and as a coolant in some nuclear reactors </li></ul><ul><li>Chlorine is used as to produce pesticides, manufacture polyvinyl chloride and as a disinfectant </li></ul><ul><li>At Cathode (- electrode) </li></ul><ul><li>Reduction: 2Na + (l) + 2 e - ------2Na(l) </li></ul>notice
  12. 12. Electrolysis of Molten Sodium Chloride <ul><li>At Anode (+ electrode) </li></ul><ul><li>2Cl - (l) ------Cl 2(g) + 2e - </li></ul><ul><li>Overall reaction: </li></ul><ul><li>2NaCl (l) electrolysis 2Na (l) + Cl 2(g) </li></ul>
  13. 13. Electroplating <ul><li>This is the deposition of a thin, very thin ( 10 -5cm ) layer of metal on an object in an electrolytic cell </li></ul><ul><li>Gold, silver, copper, nickel and chromium are the most commonly used to plate on other objects </li></ul>
  14. 14. Electroplating <ul><li>Example: to plate silver on an object </li></ul><ul><li>Make Ag the anode and the object the cathode </li></ul><ul><li>At the anode the silver becomes oxidized ( Ag + ) and these ions migrate to the cathode where they become reduced on the object ( Ag + + e - -----Ag) </li></ul>
  15. 15. Electroplating <ul><li>Makes things resist corrosion, shiny, more appealing also can be used to make metal molds ( DVD’s or phonographs) </li></ul><ul><li>In electrowinning impure metals can be purified in electrolytic cells </li></ul><ul><li>Electropolishing is another process which removes a thin layer of metal to give a high polish </li></ul>

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