Electroplating (WJEC GCSE Chemistry)

What is electroplating?

• Electroplating is a process where the surface of one metal is coated with a layer of a different metal
• The anode is made from the pure metal you want to coat your object with
• The cathode is the object to be electroplated
• The electrolyte is an aqueous solution of a soluble salt of the pure metal at the anode
  
  

Electroplating a strip of iron with tin

A piece of iron being electroplated with tin. The electrolyte is tin(II) chloride, a water-soluble salt of tin

• At the anode: Tin atoms lose electrons (is oxidised) to form tin ions in solution
• At the cathode: Tin ions gain electrons (is reduced) to form tin atoms which deposit on the strip of iron metal, coating it with a layer of tin

What is electroplating used for?

• Electroplating is done to make metals more resistant to corrosion or damage
  • E.g. chromium and nickel plating
• It is also done to improve the appearance of metals,
  • E.g. coating cutlery and jewellery with silver 

Higher Tier

How is copper purified? 

• The electrolysis of aqueous CuSO₄ using graphite rods produces oxygen and copper
• By changing the electrodes from graphite to pure and impure copper, the products can be changed at each electrode
• Electrolysis can be used to purify metals by separating them from their impurities
• In the set-up, the impure metal is always the anode, in this case the impure copper
• The cathode is a thin sheet of pure copper
• The electrolyte used is an aqueous solution of a soluble salt of the pure metal at the anode, e.g. CuSO₄
• Copper atoms at the anode lose electrons and go into solution as ions:

Cu ⟶ Cu²⁺  +  2e

• The anode thus becomes thinner due to loss of atoms and the impurities fall to the bottom of the cell as sludge
• The copper(II) ions are attracted to the cathode where they gain electrons and form now purified copper atoms
• The cathode gradually becomes thicker

Cu²⁺  +  2e^- ⟶ Cu

• The anode sludge is a highly valuable material and is further refined as it often contains small quantities of precious metals like silver which are found as impurities in the unrefined copper

Purification of copper 

The cathode increases in mass and the anode decreases in mass