Chome plated metal. Image credit MediaWiki

Chome plated metal. Image credit MediaWiki

ZIMSEC O Level Combined Science Notes: The electroplating process

  • Metals can be protected from corrosion by plating (covering) them with a less reactive metal
  • The metal which does not react with oxygen protects the more reactive metal underneath it
  • From oxidising with air
  • Copper, chrome and nickel are used to plate more reactive metals
  • This is because they are less susceptible to corrosion
  • Silver and Jewelry and ornaments
  • Metals are cleaned thoroughly before the process begins
  • They are placed in a bath of concentrated hydrochloric acid to remove the corroded metal
  • A current is then passed through a solution of metal ions
  • The object to be plated becomes the cathode/negative
  • The anode supplies the metal ions
  • Positive metal ions move to the cathode where they pick up electrons and become atoms which then coat the cathode

Copper plating

  • Copper cyanide or
  • copper sulphate is used as the electrolyte which is acidified using sulphuric acid
  • The copper cyanide solution is alkaline and gives a plate that adheres better
  • But the resulting coat has a dull finish
  • It is used to plate motor car parts that get very hot for example silencers
  • The acid electrolyte gives a bright finish and is used on decorative objects
  • both methods use copper anodes

Tin plating

  • Tin is not as inert (unreactive) as copper
  • It however is resistant to corrosion because it forms an oxide coat
  • It is used as a protective plating for mild steel for example in making “tin” cans used for food
  • The steel is coated either by being dipped in molten tine or using the electrolytic process
  • The tin-plated does not corrode until the tin coat is scratched

Nickel plating

  • An acidic solution of nickel sulphate is used
  • And nickel anodes
  • The temperature of the electrolytic bath must be around 70°C and have a pH of about 4

Chrome plating

  • Chrome is less reactive than iron
  • Chromium plated steel is first electroplated with nickel and then
  • Plated using chromium which gives a shiny finish
  • It is used to plate door handles, taps and car bumpers
  • Chromic acid is used as the electrolyte
  • A catalyst is added to increase the plating power of the electrolyte
  • The electrolyte is kept at a temperature of about 40°C

To access more topics go to the Combined Science Notes page.


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