Applications of Electrolysis

electroplating

one metal is coated with another metal

the item which is to be plated acts as the...

cathode

the bar of the metal with which the item is being plated acts as the...

anode

In simple electroplating of objects in aqueous solutions of metal ions, it is...

- not possible to electroplate using metal ions which are weaker oxidising agents than H₂O (Mn²⁺ ions and upwards on the table)

- if attempted, water will be reduced in preference to the metal ions and hydrogen gas will be formed instead of the plated metal

Why does impure copper have to be electrorefined?

the impurities reduce the conductivity of the coppper and if it is to be used in electrical wires it must be refined (purified)

main impurities in impure copper

silver, platinum, zinc, iron, gold

the impure copper acts as the...

anode

a very thin sheet of pure copper acts as the...

cathode

The thin sheet of copper is then...

copper plated while the impure copper is used up

What happens to the impurities in impure (blister) copper? (metals above Cu on the SEP table)

- these metals are stronger reducing agents than Cu

- when these metals are in contact with the solution, they will be oxidised and form ions in the solution

- however, these impure metal ions are weaker oxidising agents than Cu²⁺ and hence will not be reduced at the cathode - hence maintaining the purity of the copper cathode

- these metals can then be extracted from the solution using other methods at the end of the process

What happens to the impurities in impure (blister) copper? (metals below Cu on the SEP table)

- these metals are weaker reducing agents than Cu

- when these metals are in contact with the solution, they will not be oxidised, they remain as unreacted metal

- to ensure this, the voltage supplied to the cell is kept very low (0,2 - 0,4V)

- as the anode is 'eroded', the remaining unreacted metal eventually falls off the anode and collects in a pile under the anode, but still in metal form - 'anode sludge'

- the metals in the 'anode sludge' are sold to other refiners to extract them as they are highly valuable