Electrolysis molten substances

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Electrolysis molten substances

  1. 1. Electrolysis
  2. 2. Electrolysis of Molten substances
  3. 3. Ionic compound Positive ion Negative ion Sodium Chloride NaCl Lead (ll) Oxide PbO Magnesium Chloride MgCl2 Zinc Bromide ZnBr2
  4. 4. Ionic compound Positive ion Negative ion Sodium Chloride NaCl Na+ Cl- Lead (ll) Oxide PbO2 Pb2+ O2- Magnesium Chloride MgCl2 Mg2+ Cl- Zinc Bromide ZnBr2 Zn2+ Br-
  5. 5. Which is electrolyte and non- electrolyte? • Sodium Chloride • Lead (ll) Oxide • Magnesium Chloride • Zinc Bromide These ionic compounds are electrolytes
  6. 6. The term electrolysis was introduced by Michael Faraday. • ‘Lysis’ means loosening in Greek. • Thus electrolysis means ‘loosening by electricity’.
  7. 7. Electrolysis Electrolysis is a process occurs when electricity is pass through a solution (electrolyte) and cause it to decompose into its constituent elements.
  8. 8. Electrolytes are substances able to conduct electricity in [ ] state or [ ] state and undergo [ ] change. Electrolysis is a process where the [ ] are broken down into its [ ] elements by passing [ ] through it. electrolytes molten chemical liquid electricity constituent
  9. 9. Electrolytes are substances able to conduct electricity in [molten] state or [liquid] state and undergo [chemical] change. Electrolysis is a process where the [electrolytes] are broken down into its [constituent] elements by passing [electricity] through it.
  10. 10. Electrolytic Cell The electrolytic cell is the set of apparatus needed to conduct electrolysis.
  11. 11. Electrolytic cell consists of •a battery connected to a switch in series with •2 metal plates called electrodes. Electrodes will carry electricity to the electrolyte.
  12. 12. Electrolytic Cell Battery Electrolyte Metal Plates (Electrodes) ammeter
  13. 13. a)Electrode connected to the positive terminal of an electric source is called anode. b)Electrode connected to the negative terminal of an electric source is called cathode.
  14. 14. Anode (+) Cathode (-)
  15. 15. • When electric current is allowed to pass through, the electrolytes which are ionic compound will split up into positive (+) and negative (-)ions. • Example: NaCl Na+ + Cl- Ionic compound +ve ion -ve ion
  16. 16. • Ions will migrate to the oppositely charged electrodes. • Negatively charged (-) ions will move to the positively charged anode (+). Therefore called anions. • Positively charged (+) ions will move to the negatively charged cathode (-) and are called cations.
  17. 17. • At the anode, the negative ions will lose their electrons to the anode. • Anode will readily accepts electrons because it is positively charged. ANODE
  18. 18. CATHODE • At the cathode, the positively charged cations will accept electrons from the cathode. • This discharging of ions at the electrode results in chemical decomposition of the electrolyte. • The movement of ions allows electricity to be conducted.
  19. 19. When describing electrolysis, state: • The ions present in the electrolyte • The movement of ions to the anode and cathode • Half equation at the anode and cathode
  20. 20. Electrolysis of Molten Lead (ll) Bromide PbBr2
  21. 21. • Lead (ll) bromide is an ionic compound electrolyte. • PbBr2 consist of lead (ll) cations, Pb2+ and bromide anions, Br-. • In solid lead (ll) bromide, these ions do not move freely but are held in fixed positions in lattice.
  22. 22. • It can only can conduct electricity when dissolved in water or in molten state.
  23. 23. Molten lead (ll) bromide Crucible Electrolysis of molten lead (ll) bromide
  24. 24. • A bulb is connected to the circuit to show when the electricity is flowing. • Carbon electrodes are used because it will not react with the products formed. • When a current is passed through the molten lead bromide, lead (ll) cations, Pb2+ and bromide anions, Br- are formed.
  25. 25. •Bromide anions which are negatively charged are attracted to the positive anode. •Lead (ll) cations which are positively charged are attracted to the negative cathode.
  26. 26. ANODE •Bromide ions will move towards anode. •At anode, each bromide ion will release an electron to form a neutral bromine atom. •Two bromine atoms combine to form bromine gas. •Thus, bromine gas evolves at the anode.
  27. 27. • Lead (ll) cations attracted to cathode. • At the cathode, each lead (ll) ion accept 2 electrons to form lead atom. • Hence, silvery lead globule deposited. CATHODE
  28. 28. Pb2+, Br- Br- Pb2+ release accept 1 2 bromine gas evolves silvery grey globule
  29. 29. Half Equation Half equation is equation used to show the reaction occur at the anode or cathode.
  30. 30. • Bromide ion, Br- releases an electron to form a bromine atom, Br. Br- Br + e- • Two bromine atoms combine to form a bromine gas, Br2 molecule. Br + Br Br2 Half equation: 2 Br- (l) Br2 (g) + 2e- ANODE
  31. 31. • lead (ll) ion, Pb2+ accept 2 electrons to form lead atom. Half equation: Pb2+ (l) + 2e- Pb (s) CATHODE
  32. 32. Combining the two half equations, we get the overall equation that represent the electrolysis of molten lead (ll) bromide Anode: 2 Br-(l) Br2 (g) + 2e- Cathode: Pb2+ (l) + 2e- Pb (s) Pb2+ (l) + 2 Br- (l) Pb (s) + Br2 (g)
  33. 33. Electrolysis of Molten Lead (ll) Oxide PbO
  34. 34. Pb2+, O2- O2- Pb2+ release accept 2 2 oxygen gas evolves silvery grey globule
  35. 35. • The Pb2+ ions move towards the cathode • The O2- ions move towards the anode • At cathode,  a lead (ll) ion accepts two electrons to form a lead atom. • At anode,  an oxide ion releases two electrons to form an oxygen atom.  Two oxygen atoms combine to form one molecule of oxygen gas.
  36. 36. Half Equation ANODE Anode: 2 O-(l) O2 (g) + 2e- CATHODE Cathode: Pb2+ (l) + 2e- Pb (s) Pb2+ (l) + 2 O- (l) Pb (s) + O2 (g) Overall Equation
  37. 37. Web Link • You can find out more about electrolysis of molten compound. TRY THESE: • http://www.mcwdn.org/chemist/pccha nge.html

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