This set of Chemistry Multiple Choice Questions & Answers (MCQs) focuses on “Refining”.
1. Refining is not an important process in metallurgy.
Explanation: The metals obtained by the metallurgical processes are impure and contain several unwanted impurities such as other metals, non-metals, unreacted compounds and so on. Hence, refining is an important process to ensure the purity of the metal.
2. Which of the following is not an impurity generally present in crude metals?
a) Other metals
c) Unreacted oxides
d) Pine oil
Explanation: The impurities generally present in crude metals consist of other metals, formed by reduction of their respective oxides present in the ore, non-metals such as silicon and phosphorus, unreacted oxides and sulphides of the metals and substances taken up in the furnace such as slag.
3. Which of the following metals cannot be refined by distillation?
Explanation: Distillation process is used for refining metals that are usually volatile in nature. Zinc, cadmium and mercury are refined vial distillation where the pure metal distils over, leaving behind the non-volatile impurities.
4. Zone refining is also called fractional crystallization.
Explanation: Zone refining is a method of purification or refining of crude metals which is extremely useful for producing metals of very high quality. It is also known as fractional crystallization as the pure metal crystallizes out in the process.
5. Which of the following processes is used to purify lead?
c) Electrolytic refining
d) Zone refining
Explanation: Liquation is used for purification of metals that contain impurities which are less fusible than the metals themselves, that is, the melting points of the metals are lower than that of the impurities. Lead is refined by liquation process.
6. What is the anode made up of in electrolytic refining?
a) Impure metal
b) The metal ore
c) Pure metal
d) Double salt of metal
Explanation: In electrolytic refining, the impure metal is converted to a block which forms the anode while the cathode is made up of a pure strip of the same metal. The electrolyte used is generally a solution of a soluble salt of the metal, usually, a double salt of the metal.
7. What is the purity range for copper obtained from electrolytic refining?
Explanation: The result of electrolytic refining is the transfer of pure metal from the anode to the cathode. The impurities of more basic metals remain in the electrolytic solution as ions and that of less basic metals settle down as anode mud. Copper refined through electrolysis is 99.95-99.99% pure.
8. Which of the following is an electrolyte used during the electrolytic refining of copper?
a) Copper sulphate solution
b) Copper sulphate solution acidified with sulphuric acid
c) Sulphuric acid
d) Copper chloride
Explanation: In the electrolytic refining of copper, crude copper or blister copper is made the anode, a thin sheet of pure copper is made the cathode and a solution of copper sulphate acidified by sulphuric acid is used as the electrolyte.
9. Which of the following is not refined by zone refining method?
Explanation: Zone refining is based on the principle that the impurities are more soluble in the molten state than in the solid state of the metal. Semiconductors such as germanium, silicon and gallium are refined by zone refining. Gold is generally refined via electrolysis.
10. Why is zone refining carried out in an inert atmosphere?
a) To prevent reduction of metal
b) To prevent oxidation of metal
c) To reduce the external pressure
d) To reduce the external temperature
Explanation: In zone refining, when the melt of an impure metal is allowed to cool, the pure metal crystallizes out while the impurities remain in the melt. This process is usually carried out in an inert atmosphere to prevent the oxidation of the metal.
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