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

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