(a) Differentiate between roasting and calcination with balanced chemical equations using zinc ores as examples. (b) Exp

Question

(a) Differentiate between roasting and calcination with balanced chemical equations using zinc ores as examples.

(b) Explain the process of electrolytic refining of copper with a clear description of the setup, electrodes used, and the chemical reactions involved at both electrodes.

Accepted Answer

Part (a): Difference Between Roasting and Calcination Roasting: Definition: Roasting is the process in which a sulphide ore is strongly heated in the presence of excess air to convert it into a metal oxide. Example (Zinc Sulphide / Zinc Blende): $$2ZnS(s) + 3O2(g) \xrightarrow{\Delta} 2ZnO(s) + 2SO2(g)$$ Gaseous By-product: Sulfur dioxide ($SO2$) gas is released. Calcination: Definition: Calcination is the process in which a carbonate ore is strongly heated in the absence or limited supply of air to convert it into a metal oxide. Example (Zinc Carbonate / Calamine): $$ZnCO3(s) \xrightarrow{\Delta} ZnO(s) + CO2(g)$$ Gaseous By-product: Carbon dioxide ($CO2$) gas is released. Reduction of Oxide to Metal: The obtained zinc oxide ($ZnO$) is subsequently reduced to metallic zinc using a reducing agent such as carbon (coke): $$ZnO(s) + C(s) \xrightarrow{\Delta} Zn(s) + CO(g)$$ --- Part (b): Electrolytic Refining of Copper 
Electrolytic refining is the process used for purifying crude metals obtained after extraction. Experimental Setup: Anode (Positive Electrode): A thick block of crude or impure copper metal. Cathode (Negative Electrode): A thin strip of pure copper metal. Electrolyte: An aqueous solution of acidified copper sulphate ($CuSO4$). Working Mechanism: When an electric current is passed through the electrolyte, pure copper metal from the impure anode dissolves into the electrolyte solution. Simultaneously, an equivalent amount of pure copper ions from the electrolyte gets deposited on the cathode. Chemical Reactions at Electrodes: At Anode (Oxidation): Impure copper loses electrons and dissolves into the solution as copper ions. $$Cu(s) 	ext{ (impure)} ightarrow Cu^{2+}(aq) + 2e^-$$ At Cathode (Reduction): Copper ions from the electrolyte solution gain electrons and get deposited as pure copper metal. $$Cu^{2+}(aq) + 2e^- ightarrow Cu(s) 	ext{ (pure)}$$ Anode Mud: Soluble impurities present in the crude copper dissolve into the electrolyte solution. Insoluble impurities (such as precious metals like gold and silver) settle down at the bottom of the anode tank, which is known as anode mud.

Metals and Non-metals

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