General Principles and Processes of Isolation of Elements Important Questions

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Very Short Answer Questions (1 Mark Questions)

Ques. Write a non-exothermic reaction taking place in the blast furnace during the extraction of iron.

Ans. The non-exothermic reaction that takes place in the blast furnace during the extraction of iron is CaCO₃ → CaO + CO₂

Ques. Name the method of refining of metals such as germanium.

Ans. Zone refining is the method used for the refining of metals.

Ques. Name the impurities present in bauxite ore.

Ans. The impurities present in bauxite ore are SiO₂, Fe₂O₃, and TiO₂.

Ques. What are collectors in the froth flotation process? Give one example.

Ans. Collectors enhance the non-wettability of ore particles. One such example is pine oil.

Ques. What is the composition of copper matte?

Ans. Copper matte is composed of Cu₂S and FeS.

Ques. Which form of copper is called blister copper?

Ans. The solidified copper obtained has a blistered appearance due to the evolution of sulfur dioxide so it is called blister copper.

Ques. What are the constituents of German silver?

Ans. The constituents of German silver are Cu (25 - 30%), Zn (25 - 30%), and Ni (40-50%).

Ques. Name the method of refining which is based on the principle of adsorption.

Ans. Chromatography is a method that is based on the principle of adsorption.

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Short Answer Questions (2 Marks Questions)

Ques. Name the process for the benefaction/concentration of (i) an ore having lighter impurities (ii) sulfide ore.

Ans. (i) The process of concentration of an ore having lighter impurities is termed gravity separation.

(ii) The process of concentration of sulfide ore is termed froth floatation.

Ques. How is copper extracted from a low-grade ore of it? 

Ans. Copper is extracted by hydrometallurgy from low-grade ores. Then, it is leached out using acid or bacteria. The solution containing copper ions (Cu²⁺) is treated with scrap iron or H₂ as

Cu₂ + H₂(g) → Cu (s) + 2H (aq)

In this way, copper is obtained.

Ques. Although aluminum is above hydrogen in the electrochemical series, it is stable in air and water. Why?

Ans. Aluminum is above hydrogen in the electrochemical series yet it is stable in air and water due to the formation of inert oxide Al₂O₂.

Ques. Give the names and formulae of three ores that are concentrated by the froth floatation process.

Ans. The names and the formula of ores concentrated by froth floatation method are as follows

(i) Galena: PbS 

(ii) Zinc blende: ZnS 

(iii) Cinnabar: HgS

Read More: Extraction of Zinc

Ques. What is pyrometallurgy? 

Ans. Pyrometallurgy is the process of reduction of a metal oxide by heating with coke or another reducing agent like aluminum, magnesium, etc. 

Ques. Among Fe, Cu, Al, and Pb, which metal (s) cannot be obtained by smelting? 

Ans. In the given metals, Aluminum can not be obtained by smelting. 

Ques. Explains the principles behind the electrolytic refining method for metals. Write the two main requirements of the Mond process and Van Arkel method for the refining of a metal.

Ans. Mond process is used to refine nickel, while the Van Arkel method is used to refine titanium. For instance, the refining of nickel is done with vapor phase refining, the method is known as the Mond process. This method is based on the principle that some metals are converted into their volatile compounds, and impurities are not affected in compound formation.

Ques. How is copper extracted from low-grade copper ores?

Ans. Copper is extracted from low-grade copper ore using the hydrometallurgy method. For this purpose, the ore is leached out using bacteria. The solution that contains Cu²⁺ is treated with scrap iron and H₂.

Cu²⁺ (aq) + H₂ (g) → Cu (s) + 2H+ (aq)

Ques. Name the elements present in anode mud during the refining of copper. Why does it contain such elements?

Ans. The elements present in anode mud during the refining of copper are Au and Ag. These elements are not oxidized at the anode and are less electropositive than copper.

Ques. Name the process for the benefaction/concentration of (i) an ore having lighter impurities (ii) sulfide ore.

Ans. (i)The process of concentration of an ore having lighter impurities is termed gravity separation.

(ii) The process of concentration of sulfide ore is termed froth floatation.

Read More: General Principles & Processes Of Isolation Of Elements MCQs

General Principles and Processes of Isolation of Elements

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Long Answer Questions (3 Marks Questions)

Ques. What should be the considerations during the extraction of metals by the electrochemical method?

Ans. The following considerations are to be made during the extraction of metals by the electrochemical method:

• Reactivity of the metal produced.
• Electrodes to be made of suitable material.
• Addition of flux for making molten mass conducting.

.Ques. Define (i) Roasting (ii) Calcination (Comptt. Delhi 2014)

Ans. (i) Roasting: The process of heating the concentrated sulfide ore strongly in the presence of air is known as roasting.

2ZnS + 3O₂ → 2ZnO + 2SO₂ ↑

(ii) Calcination: The process of heating the concentrated ore strongly in the absence of air is known as calcination.

ZnCO₃ ⟶Δ ZnO + CO₂ ↑

Ques. Name the methods employed for purifying the following metals along with the principle behind each one of them:

(i) Nickel 

(ii) Germanium (All India 2012)

Ans. (i) Nickel: The method employed to purify nickel is the Mond process. In this, the metal is converted into its volatile compound and collected at a different place. It is then decomposed in order to give pure metal.

(ii) Germanium: The method employed to purify germanium is Zone refining. Zone refining is based on the principle that the impurities are more soluble in the molten than in the solid state of the metal.

Ques. Write two basic requirements for refining of metal by Mond process and by Van Arkel Method.

Ans. The two basic requirements for refining metal by Mond process and Van Arkel Method are

(i) Metal should form a volatile compound with the available reagent.

(ii) The volatile compound should be easily decomposable in order to be recovered quickly.

Ques. (i) Why is the reduction of a metal oxide easier if the metal formed is in a liquid state at the temperature of reduction?

(ii) Although carbon and hydrogen are better-reducing agents, why are they not used to reduce metallic oxides at high temperatures? 

Ans. In the liquid state of the metal, the entropy is more positive as compared to the solid state so that the Gibbs free energy becomes more negative and the reduction process occurs readily.

Carbon and hydrogen are not used because carbon and hydrogen react with metals at high temperatures to form carbides and hydrides, respectively.

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Very Long Answer Questions (5 Marks Questions)

Ques. Write the role of

(i) NaCN in the extraction of gold from its ore.

(ii) Cryolite in the extraction of aluminum from pure alumina.

(iii) CO in the purification of Nickel. 

Ans. (i) Gold is leached out in the form of a complex with dil. solution of NaCN in the presence of air. Here NaCN acts as a leaching agent.

(ii) It lowers the melting point of alumina and thus makes it a good conductor of electricity.

(iii) CO forms a volatile complex with nickel which is further decomposed to give pure Ni metal. 

Ques. Explain the principle involved in each of the following processes of metallurgy:

(i) Froth floatation method

(ii) Electrolytic refining of metals

(iii) Zone refining of metals (All India 2010)

Ans. (i) Froth Floatation Method: The method of froth floatation is used for removing gangue from sulfide ores. In this process, powdered ore is mixed with collectors such as pine oils, fatty acids, etc., and froth stabilizers like cresols, and aniline which enhance the non-wettability of the mineral particles and froth stabilization respectively. The ore comes with froth and gangue remains in the solution at last.

(ii) Electrolytic Refining of Metals: In this, the impure metal is made to act as an anode and a strip of the same metal in pure form is used as a cathode. Both of them are put in suitable electrolytes containing soluble salt of the same metal. The more basic metal remains in the solution and the less basic ones go to the anode mud.

(iii) Zone Refining of Metals: This process is based on the principle that impurities are more soluble in the molten state of the metal in comparison to the solid state. A circular mobile heater is fixed at one end of a rod of impure metal. When the heater moves, the molten zone of the mod also moves along with it. As an outcome, the pure metal crystallizes out of the melt and the impurities pass to the adjacent molten zone. The process is repeated multiple times which leads to the segregation of impurities at one end of the rod. The end that has impurities is then cut off.

Ques. How are metals used as semiconductors refined? What is the principle of the method used?

Ans. Metals of high grade like germanium, silicon, etc, are used as semiconductors and are refined by the zone refining method.

Principle: This method is based upon the principle that impurities are more soluble in the molten state of metal than in the solid state

Ques. Name the principal ore of aluminum. Elaborate on the significance of leaching in the extraction of aluminum. 

Ans. The principal ore of aluminium is bauxite, Al₂O₃.2H₂O. The leaching process is used to concentrate the ore of aluminum, and bauxite, which is contaminated with impurities of silica (SiO₂), iron oxide (Fe₂O₃), titanium oxide (TiO₂), etc. Leaching is done by treating the powdered ore with a hot cone. (45%) solution of NaOH at about 473-523 K and 35-36 bar pressure.

Al₂O₃.2H₂O(s) + 2NaOH (aq) + H₂O(l) → 2Na [Al(OH)₄](aq)

The impurities of ferric oxide and silica are insoluble and are removed by filtration.

The solution containing sodium aluminate is neutralized by passing CO₂ gas and hydrated alumina is precipitated.

2Na [Al(OH)₄] (aq) + CO₂ (g) → Al₂O₃. x H₂O (s) + 2NaHCO₃(s)

Hydrated alumina is then heated to 1473 K in order to get pure alumina.

Al₂O₃ . x H₂O (On 1473k) → Al₂O₃ (s) + x H₂O(g)

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