Metals and Non-metals · Lesson 11 of 13
Refining Of Metals
“Impure metal enters at the anode and cleaner metal quietly builds up at the cathode.”
• Explain why extracted metals need refining. • Describe electrolytic refining using copper as the model. • Identify the anode, cathode and electrolyte correctly. • Explain how pure metal transfers from anode to cathode. • Explain the fate of soluble and insoluble impurities, including anode mud.
Metals obtained after extraction still contain impurities. Refining removes those impurities. Electrolytic refining uses electric current to transfer the desired metal from an impure anode to a pure cathode.
Refining Of Metals
Copper, zinc, tin, nickel, silver and gold are examples of metals that can be refined electrolytically.
Electrolytic Refining
Electrolytic Refining is the purification of a metal by transferring it from an impure anode through an electrolyte onto a pure cathode.
Electrolytic Refining Of Copper
Impure copper is the anode, a thin strip of pure copper is the cathode, and acidified copper sulphate is the electrolyte.
At The Anode
Copper from the impure anode enters the electrolyte. The anode gradually becomes smaller as copper leaves it.
At The Cathode
An equivalent amount of pure copper is deposited from the electrolyte on the cathode. The cathode therefore gains mass.
Impurities
Soluble impurities enter the solution. Insoluble impurities settle below the anode.
Anode Mud is the insoluble impurity that settles below the anode during electrolytic refining.
| Part | Copper Example | Role |
|---|---|---|
| Anode | Impure copper | Supplies copper to electrolyte |
| Cathode | Pure copper strip | Receives deposited pure copper |
| Electrolyte | Acidified copper sulphate | Carries copper ions |
| Anode mud | Insoluble impurities | Settles below anode |
Extraction Versus Refining
Extraction obtains a metal from an ore or compound. Refining begins after extraction and purifies the metal already obtained.
Problem
What would you choose for electrolytic refining of an unknown metal M?
- 1.Use impure M as the anode.
- 2.Use a thin strip of pure M as the cathode.
- 3.Use a suitable solution containing a salt of M as the electrolyte.
- 4.Insoluble impurities collect below the anode.
Quiz
What is used as the anode?
What is used as the cathode?
Where is pure metal deposited?
What happens to insoluble impurities?
What is the electrolyte in copper refining?
Practice Problems
- Describe the complete setup for electrolytic refining of copper.
- Explain what happens to copper at the anode and cathode.
- Explain the different fates of soluble and insoluble impurities.
- Define anode mud and state where it is found.
- Distinguish extraction from refining.
- For a metal M, choose anode, cathode and electrolyte and explain each choice.
Key Takeaways
• Refining removes impurities from metal obtained after extraction. • In electrolytic refining the impure metal is the anode and a pure metal strip is the cathode. • A solution of a salt of the metal acts as the electrolyte. • Pure metal is deposited on the cathode while the impure anode is consumed. • Insoluble impurities settle below the anode as anode mud.