General Principles and Processes of Isolation of Elements Quiz - ICSE Class 12 Chemistry
Free practice quiz: General Principles and Processes of Isolation of Elements (ICSE Class 12 Chemistry). 50 multiple-choice questions with answers and explanations. Play online, no sign-up needed.
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Which of the following methods is most suitable for the extraction of highly electropositive metals like sodium from their molten chlorides?
- Electrolytic reduction
- Smelting with carbon
- Froth floatation
- Leaching with cyanide
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Answer: A. Electrolytic reduction
Highly electropositive metals like sodium have very negative standard electrode potentials. Their oxides or chlorides are very stable. Electrolytic reduction of their molten salts is the most effective method for their extraction because it uses electrical energy to overcome the large negative free energy change associated with their reduction. Smelting with carbon is not suitable as carbon is less electropositive than sodium and cannot reduce sodium chloride. Froth floatation and leaching are concentration techniques, not reduction methods.
The refining of nickel is commonly done by the Mond process. This process is based on the property of nickel to form a volatile compound with carbon monoxide at moderate temperatures. What is the chemical formula of this compound?
- Ni(CO)₄
- Ni₂C
- Ni(CO)₅
- NiC₂O₄
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Answer: A. Ni(CO)₄
The Mond process is used for the purification of nickel. In this process, impure nickel is heated in a stream of carbon monoxide at about 330-350 K. Nickel reacts with carbon monoxide to form nickel tetracarbonyl, Ni(CO)₄, which is a volatile liquid. Impurities like iron and copper do not react with carbon monoxide under these conditions. The volatile Ni(CO)₄ is then decomposed at about 450-470 K to deposit pure nickel as a fine powder (Ni(CO)₄ → Ni + 4CO).
Which of the following methods is suitable for the extraction of tin from stannic oxide (SnO₂)?
- Electrolytic reduction of molten SnO₂
- Reduction of SnO₂ with hydrogen
- Reduction of SnO₂ with carbon
- Reduction of SnO₂ with aluminium
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Answer: C. Reduction of SnO₂ with carbon
Tin is extracted from its principal ore, cassiterite (SnO₂), by reduction with carbon in a reverberatory furnace or a blast furnace. The reaction is: SnO₂(s) + 2C(s) → Sn(l) + 2CO(g). While hydrogen can also reduce tin oxide, carbon is more economical for large-scale industrial production. Electrolytic reduction of molten SnO₂ is not the primary method. Aluminium is a stronger reducing agent but is more expensive than carbon.
Which of the following is NOT a reducing agent used in the extraction of metals?
- Carbon monoxide
- Carbon
- Aluminium
- Oxygen
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Answer: D. Oxygen
Reducing agents are substances that donate electrons or cause reduction in other substances. Carbon monoxide, carbon, and aluminium are all commonly used as reducing agents in the extraction of metals. Oxygen, on the other hand, is an oxidizing agent; it causes oxidation by accepting electrons or by oxidizing other substances.
The term 'smelting' is best described as:
- The process of heating an ore in the absence of air
- The process of heating an ore with a flux and a reducing agent
- The process of dissolving a metal from its ore
- The process of purifying a metal by electrolysis
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Answer: B. The process of heating an ore with a flux and a reducing agent
Smelting is a pyrometallurgical process that involves heating an ore, typically in a furnace, with a flux and a reducing agent to a high temperature, causing chemical reduction and phase change to extract the desired metal in a molten state. This process is used to separate the metal from its ore and impurities.