MP Board · Class 10 · Science · Metals and Non-metalsExplain the process of extraction of metals of medium reactivity from their carbonate and sulphide ores with balanced chemical equations. Also, describe the process of refining impure copper by the electrolytic method with a neat diagrammatic description.

Extraction of Metals of Medium Reactivity

\nMetals in the middle of the activity series (such as Zinc, Iron, Lead, Copper) are usually present as sulphides or carbonates in nature. It is easier to obtain a metal from its oxide than from its sulphides or carbonates. Therefore, prior to reduction, the metal sulphides and carbonates must be converted into metal oxides.

1. Roasting

• Definition: The sulphide ores are converted into oxides by heating strongly in the presence of excess air.
• Chemical Reaction: $$2\text{ZnS (s)} + 3\text{O}_2\text{ (g)} \xrightarrow{\Delta} 2\text{ZnO (s)} + 2\text{SO}_2\text{ (g)}$$

2. Calcination

• Definition: The carbonate ores are changed into oxides by heating strongly in limited air (or absence of air).
• Chemical Reaction: $$\text{ZnCO}_3\text{ (s)} \xrightarrow{\Delta} \text{ZnO (s)} + \text{CO}_2\text{ (g)}$$

3. Reduction of Metal Oxide to Metal

• The obtained metal oxides are then reduced to the corresponding metals by using suitable reducing agents such as carbon (coke).
• Chemical Reaction: $$\text{ZnO (s)} + \text{C (s)} \rightarrow \text{Zn (s)} + \text{CO (g)}$$

Electrolytic Refining of Copper

\nMany metals produced by various reduction processes contain impurities. They are purified using electrolytic refining.

• Experimental Setup:

  • Anode: A thick block of impure copper metal.
  • Cathode: A thin strip of pure copper metal.
  • Electrolyte: An acidified solution of copper sulphate ($\text{CuSO}_4$).

• Working Mechanism:

  • On passing electric current through the electrolyte, pure copper from the anode dissolves into the electrolyte.
  • An equivalent amount of pure copper from the electrolyte gets deposited on the cathode.

• Chemical Reactions at Electrodes:

  • At Anode (Oxidation): $$\text{Cu (impure)} \rightarrow \text{Cu}^{2+} + 2e^-$$
  • At Cathode (Reduction): $$\text{Cu}^{2+} + 2e^- \rightarrow \text{Cu (pure)}$$

• Anode Mud: The soluble impurities go into the solution, whereas the insoluble impurities settle down at the bottom of the anode and are known as anode mud.