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Electrolysis molten substances

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  • 1. Electrolysis
  • 2. Electrolysis of Molten substances
  • 3. Ionic compound Positive ion Negative ion Sodium Chloride NaCl Lead (ll) Oxide PbO Magnesium Chloride MgCl2 Zinc Bromide ZnBr2
  • 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. Which is electrolyte and non- electrolyte? • Sodium Chloride • Lead (ll) Oxide • Magnesium Chloride • Zinc Bromide These ionic compounds are electrolytes
  • 6. The term electrolysis was introduced by Michael Faraday. • ‘Lysis’ means loosening in Greek. • Thus electrolysis means ‘loosening by electricity’.
  • 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. 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. 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. Electrolytic Cell The electrolytic cell is the set of apparatus needed to conduct electrolysis.
  • 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. Electrolytic Cell Battery Electrolyte Metal Plates (Electrodes) ammeter
  • 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. Anode (+) Cathode (-)
  • 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. • 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. • 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. 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. 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. Electrolysis of Molten Lead (ll) Bromide PbBr2
  • 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. • It can only can conduct electricity when dissolved in water or in molten state.
  • 23. Molten lead (ll) bromide Crucible Electrolysis of molten lead (ll) bromide
  • 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. •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. 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. • 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. Pb2+, Br- Br- Pb2+ release accept 1 2 bromine gas evolves silvery grey globule
  • 29. Half Equation Half equation is equation used to show the reaction occur at the anode or cathode.
  • 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. • lead (ll) ion, Pb2+ accept 2 electrons to form lead atom. Half equation: Pb2+ (l) + 2e- Pb (s) CATHODE
  • 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. Electrolysis of Molten Lead (ll) Oxide PbO
  • 34. Pb2+, O2- O2- Pb2+ release accept 2 2 oxygen gas evolves silvery grey globule
  • 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. 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. 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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