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General Principles and processes of isolation of elements deals with the processes in extraction and isolation of metals from their sources. The compound of a metal found in nature is called a mineral which is abundant in the earth’s crust. The minerals which are naturally occurring, homogeneous inorganic solid substances having a definite chemical composition and characteristic crystalline structure, color, and hardness from which metals can be economically and conveniently extracted are called ores. Metals are extracted from their respective ores. An ore is usually contaminated with earthy or undesired materials which is commercially worthless material surrounding a wanted mineral in an ore deposit known as gangue.
Multiple Choice Questions
Ques 1. The metal M in the equation is,
4M + 8CN– + H2O + O2 → 4[M(CN)2]– + 4OH–
- Copper
- Iron
- Gold
- Zinc
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Answer: (c) Gold
Explanation: The complete reaction is:
4Au + 8CN– + H2O + O2 → 4[Au(CN)2]– + 4OH–
Ques 2. In the following reactions, Zinc in the extraction of gold acts as:
4M + 8CN– + H2O + O2 → 4[M(CN)2]– + 4OH–
2[Au(CN)2]- + Zn → 2Au + [Zn(CN)4]2-
- Flux
- Oxidizing agent
- Reducing Agent
- Decomposing Agent
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Answer: (c) Reducing Agent
Explanation: In the above reactions, the Zinc has changed its state from 0 to +2 so in this process, zinc is getting oxidized and it is acting as a reducing agent.
Ques 3. The principle upon which the method of zone refining of metals is based is:
- Greater noble characteristics of solid metal than that of the impurity
- Greater mobility of pure metal than impurity
- Higher melting point for the impurity than that of pure metal.
- Greater solubility of the impurity in molten state than in solid
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Answer: (d) greater solubility of the impurity in molten state than in solid
Explanation: The principle on which the method of zone refining of metals is based is greater solubility of the impurity in the molten state than in the solid. Some elements that are used as semiconductors like Si, Ge, Ga etc. are refined by this method.
Ques 4. Cryolite is added to the charge in the electrolytic method of obtaining aluminum from purified bauxite, in order to:
- Lower the melting point of bauxite
- Dissolve bauxite providing it with a conduction of electricity
- Protect aluminum produced from oxygen
- Minimize the heat loss due to radiation
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Answer: (b) dissolve bauxite providing it with a conduction of electricity
Explanation: In the electrolytic method for obtaining aluminum from purified bauxite, cryolite is added to charge because it reduces the melting point of Bauxite (from 12000C to 8000C-9000C). It also increases electrical conductivity of the mixture.
Ques 5. What is the formula for copper pyrite:
- Cu2S
- CuFeS
- CuFeS2
- Cu2Fe2S2
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Answer: (c) CuFeS2
Explanation: Copper Pyrite has the chemical formula CuFeS2 and it forms crystals in the tetragonal system.
Ques 6. When we remove unwanted materials like sand, clays, etc. from the ore, it is known as ____, ____or ____
- Concentration, dressing, benefaction
- Separation, refining, gangue
- Magnetic separation, purification, gangue
- Washing, refining, amalgamation
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Answer: (a) Concentration, Dressing, Benefaction
Explanation: The removal of unwanted materials such as clay, sand etc. from the ore is known as concentration, benefaction or dressing.
Ques 7. In the froth floatation method, which of the following ores is used for concentration?
- Haematite
- Zinc blende
- Magnetite
- Camallite
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Answer: (b) Zinc blende
Explanation: The process used for the concentration of Zinc blende is the Froth Floatation Method because it is a sulfide ore . The resultant ore obtained from the process is concentrated and is then roasted in excess air at 1200K to obtain zinc oxide (ZnO).
Ques 8. The method of concentration in which the powdered ore is treated with a running stream of water and the heavy ore particles and lighter impurities are separated is known as
- Metallurgy
- Leaching
- Froth floatation process
- Gravity separation
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Answer: (c) Froth floatation method
Explanation: The method of concentration in which the powdered ore is treated with a running stream of water and the heavy ore particles and lighter impurities are separated is known as froth floatation method.
Ques 9. In froth floatation method, the oil which is used as a frothing agent is
- Coconut oil
- Castor oil
- Palmitic oil
- Pine oil
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Answer: (d) Pine oil
Explanation: In the froth floatation method, the oil which is used as a frothing agent is pine oil.
Ques 10. Why is the leaching in the extraction of aluminum important:
- It helps in the removal of the impurities like SiO2, Fe2O3 etc. from the bauxite ore
- It converts the ore into oxide
- It reduces melting point of the ore
- It eliminates water from bauxite
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Answer: (a) it helps in the removal of the impurities like SiO2, Fe2O3 etc. from the bauxite ore
Explanation: The Importance of leaching in the extraction of aluminum is to concentrate pure alumina (Al2O3) from bauxite ore. In the process of leaching, the hydrated Al2O3 gets precipitated and the sodium silicate still remains in the solution.
Ques 11.The method by which the ore is concentrated by using the difference in density between ore and impurities is called
- Levigation
- Leaching
- Magnetic separation
- Liquefaction
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Answer: (a) Levigation
Explanation:The method by which the ore is concentrated by using the difference in density between ore and impurities is called Levigation where a powdered ore is treated with a stream of running water and in the process the lighter gangue particles are washed away and heavier ore particles are left behind.
Ques 12. Which of the following makes up the inner lining of a blast furnace:
- Graphite bricks
- Silica bricks
- Fire clay bricks
- Basic bricks
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Answer: (c) Fire clay bricks
Explanation: The fire clay bricks make up the inner lining of the blast furnace and are highly refractory in nature which do not melt at even huge temperatures. The main components from which fire clay bricks are made up of are Silica and alumina.
Ques 13. The method which is generally used for the extraction of metal from oxide ore is
- Reduction by carbon
- Aluminum reduction
- Hydrogen reduction
- Electrolytic reduction
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Answer: (a) Reduction by Carbon
Explanation: The method which is generally used in the extraction of metals from oxide ore involves reduction with carbon.
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