Copper sulfate and electroplating
Electrolysing copper(II) sulfate
- With inert carbon electrodes: copper forms at the cathode, oxygen at the anode; the blue colour slowly fades as copper is removed.
- With copper electrodes: copper forms at the cathode while the anode dissolves; the blue colour stays the same. This is used to purify copper.
Practice
Electrolysing copper(II) sulfate with carbon electrodes causes the blue colour to:
With inert carbon electrodes, copper is deposited and oxygen forms at the anode, so the blue fades.
Practice
To purify copper, the impure copper is used as the:
The impure copper anode dissolves and pure copper deposits on the cathode.
Electroplating
- Electroplating coats a metal object with a thin layer of another metal (better looks + resists corrosion).
- To electroplate:
- the object to be coated → the cathode,
- the plating metal → the anode,
- the electrolyte → a solution of the plating-metal ions.
Practice
When electroplating an object, the object is made the:
The object to be coated is the cathode; the plating metal is the anode.
You've got it
Key idea
- copper sulfate with carbon electrodes: blue fades (copper out at cathode, oxygen at anode)
- copper sulfate with copper electrodes: blue stays (anode dissolves) — used to purify copper
- electroplating: object = cathode, plating metal = anode, electrolyte = plating-metal ions