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Saturday, June 11, 2011

Chemistry Form 4: Chapter 6 - Electrolysis of Lead (II) Bromide

  • Electrolysis is a chemical process where a substance in its molten state or in an aqueous solution decomposed by electric current.
  • This involves conversion of energy from electrical energy to chemical energy.
  • Electrodes are the strips of metals inserted into electrolyte for conduction of electricity. he metal electrode connected to the positive terminal of the battery is called the anode (+). The metal electrode connected to the negative terminal of the battery is called the cathode (-).
  • Electrolytic cell is the complete set-up for electrolysis. This consists of the vessel containing the electrolyte, anode, cathode, battery and  wires. 




At the CathodeAt the Anode
Observation
  • When electricity is flowing, a silvery deposit of lead metal forms on the cathode. In fact, as it is molten, it is more likely to drip off in a molten blob.
Observation
  • When electricity is flowing, brown fumes of bromine gas are seen at the anode.
Half equation
Pb2+ + 2e ---> Pb
Half equation
2Br- ---> Br2 + e
Explanation
  • The lead(II) ions, as they are positive, move to the negative cathode, where each ion gains two electrons to form a lead atom.
  • Any reaction at a cathode involved  a gain in electrons. This is called reduction or more exactly, cathodic reduction .
Explanation
  • The bromide ions, as they are negative, move to the positive anode, where each loses an electron to form a bromine atom.
  • Then two of these newly formed atoms combine to form bromine gas.
  • Any reaction at an anode involves a loss of electrons.

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