Thermodynamic and Electrochemical Principles of Metallurgy MCQ Quiz in தமிழ் - Objective Question with Answer for Thermodynamic and Electrochemical Principles of Metallurgy - இலவச PDF ஐப் பதிவிறக்கவும்

CONCEPT:

Reactions and Products in the Extraction of Manganese Compounds

• Metal halides (such as MnCl₂) react with aqueous sodium hydroxide (NaOH) to form metal hydroxides and sodium salts.
• Heating metal hydroxides with sulfuric acid and an oxidizing agent like lead dioxide (PbO₂) can convert them into colored manganese oxo species.
• Filtrates containing NaCl can react with concentrated sulfuric acid to produce chlorine gas, which gives a blue color with KI-starch paper.

EXPLANATION:

• Metal halide (MnCl₂) reacts with aqueous NaOH:
  • MnCl₂ + 2 NaOH → Mn(OH)₂ (P) + 2 NaCl (Q)
  • Here, Mn(OH)₂ is a white precipitate (P) and NaCl is the filtrate (Q).
• Heating Mn(OH)₂ with H₂SO₄ and excess PbO₂:
  • 2 Mn(OH)₂ + 5 PbO₂ + 4 H₂SO₄ → 2 MnO₄^- (X) + 5 PbSO₄ + 6 H₂O
  • MnO₄^-, permanganate ion (X), is a colored species (purple).
• Filtrate (NaCl) reacting with conc. H₂SO₄:
  • 2 NaCl + H₂SO₄ → Na₂SO₄ + 2 HCl
  • 4 HCl + MnO₂ → MnO(OH)₂ + Cl₂ (Y) + 2 H₂O
  • Cl₂ (Y) gives a blue color with KI-starch paper.

Therefore, the correct answers are MnO₄^- and Cl₂ respectively.

CONCEPT:

Processes Involved in the Extraction of Metals

• Roasting: This is a process in metallurgy where an ore is heated in the presence of excess air or oxygen. This process is typically used for sulfide ores. Roasting converts the metal sulfide to the metal oxide and sulfur dioxide gas is released.
• Calcination: This process involves heating the ore in the absence of air. Calcination is used to remove volatile substances, moisture, and to decompose carbonates to oxides.
• Smelting: This process involves heating an ore in the presence of a reducing agent, such as carbon, and flux, like silica, to extract the metal.
• Cyanidation: A method used for the purification of ores where the ore is treated with a cyanide solution to form a soluble complex that can be reduced to extract the pure metal.

EXPLANATION:

• Statement 1: Roasting of Malachite produces Cuprite:

  Malachite is Cu(OH)₂·CuCO₃. Upon roasting, it decomposes to form copper oxide (CuO), not cuprite (Cu₂O).

  • Cu(OH)₂·CuCO₃ → 2CuO + H₂O + CO₂

  Therefore, this statement is incorrect.

• Statement 2: Calcination of Calamine produces Zincite:

  Calamine is zinc carbonate (ZnCO₃). Calcination of zinc carbonate decomposes it to zinc oxide (ZnO) and carbon dioxide.

  • ZnCO₃ → Δ → ZnO + CO₂

  Since zincite is ZnO, this statement is correct.

• Statement 3: Copper pyrites is heated with silica in a reverberatory furnace to remove iron:

  Copper pyrites (CuFeS₂) is heated in the presence of silica (SiO₂) to remove iron as slag.

  • CuFeS₂ + O₂ → Cu₂S + FeS + SO₂
  • FeS + O₂ → FeO + SO₂
  • FeO + SiO₂ → FeSiO₃ (slag)

  Therefore, this statement is correct.

• Statement 4: Impure silver is treated with aqueous KCN in the presence of oxygen followed by reduction with zinc metal:

  Impure silver is dissolved in KCN in the presence of oxygen to form a soluble complex [Ag(CN)₂]^-.

  • 4 Ag + 8 CN^- + 2 H₂O + O₂ → 4 [Ag(CN)₂]^- + 4 OH^-

  The complex is then reduced by zinc to give pure silver and a zinc cyanide complex:

  • 2 [Ag(CN)₂]^- + Zn → [Zn(CN)₄]^2- + 2 Ag

  Therefore, this statement is correct.

Therefore, the correct statements are 2, 3, and 4.

CONCEPT:

Catalysts and Processes

• A catalyst is a substance that increases the rate of a chemical reaction without undergoing permanent chemical change itself.
• Different industrial processes use specific catalysts to achieve desired reactions efficiently.

EXPLANATION:

• Evaluate each pair of process and catalyst:
  • Pair 1: Photography - AgBr
    • Silver bromide (AgBr) is used in the photographic film, making this pair correct.
  • Pair 2: Polythene preparation - TiCl₄, Al(CH₃)₃
    • Titanium tetrachloride (TiCl₄) and trimethylaluminum (Al(CH₃)₃) are used in Ziegler-Natta catalysts for the preparation of polythene, making this pair correct.
  • Pair 3: Haber process - Iron
    • Iron is used as a catalyst in the Haber process for the synthesis of ammonia, making this pair correct.
  • Pair 4: Wacker process - PtCl₂
    • The Wacker process uses palladium chloride (PdCl₂) as the catalyst, not platinum chloride (PtCl₂), making this pair incorrect.

Therefore, the most appropriate answer is  Wacker process – PtCl₂.

The Correct answer is ​Bayer process.

Key Points

• The Bayer process is the principal method for refining bauxite to produce alumina (aluminum oxide), which is then used in the electrolytic refining process (Hall-Héroult process) to produce aluminum metal.
• The Bayer process involves dissolving bauxite in sodium hydroxide, which separates alumina from impurities.

Additional Information

• Blast furnace is primarily used for smelting iron from its ores, not for refining aluminum.
• Electrolytic refining is commonly used for purifying metals like copper, not for the initial refinement of aluminum. However, in the context of aluminum, the Hall-Héroult process follows the Bayer process and involves electrolytic reduction .
• Bessemer process is an obsolete method for converting crude iron into steel by blowing air through it to remove impurities. It is not related to aluminum production

Correct answer: 1)

Concept:

• Flux, in metallurgy, is any substance introduced in the smelting of ores to promote fluidity and remove objectionable impurities in the form of slag.
• Limestone is commonly used for this purpose in smelting iron ores. Other materials used as fluxes are silica, dolomite, lime, borax, and fluorite.

Explanation:

• The flux that is added to remove Iron oxides from its mixture with copper oxide needs to be acidic in nature because acidic reactants will react with the basic reactant.
• Iron oxides are basic because metal oxides are always basic in nature.
• The only acid flux given in the options is Silica which is an acidic flux.
• Ferrous oxide combines with silica and forms ferrous silicate.
• By this reaction, most of the iron is removed as slag.

Conclusion:

Thus, the flux that is added to form the slag is SiO2, which is an acidic flux.

Concept:

• One of the purification techniques of the ore is the calcination process.
• During this process, the small unnecessary molecules from the mineral are removed.
• For this purpose, the mineral is heated in a controlled way to a high temperature.

Explanation:

• In the absence of air, a mineral-like carbonate, and hydroxide are heated. 
• Then the carbonate ore loses carbon dioxide gas and forms the respective oxide ore.
• The hydroxide ores when heated in the absence of air (calcination) they convert into the respective oxides.

The given chemical reactions 

MgCO3 → MgO + CO2

• It is an example of calcination.
• This reaction represents the heating of carbonate ore in the absence of oxygen and is converted into its respective oxide ore.
• During this process, carbon dioxide molecule is lost.
• This is the correct choice.

Additional Information FeO + SiO2 → FeSiO3

• Involves the formation of slag FeSiO₃
• This reaction does not involve the removal of small molecules from the mineral. Therefore it is not the calcination process.
• The second chemical equation is Fe2O3 + 3C → 2Fe + 3CO an example of smelting.
• The oxide ore is heated with coke and then the metal is reduced.
• This process is known as smelting.

2ZnS + 3O2 → 2ZnO + 2SO2

• It is an example of roasting.
• Heating the sulphide ore in presence of oxygen and converting it into its respective oxide ore is called roasting.
• Therefore it is not a correct answer.

The correct answer is Option - 2.
Concept -

• Slag formed in the extraction of metals is lighter and has a lower melting point than metal so it generally appears in the upper layer of solutions as metal is heavier than slag.
• Slag is a glassy by-product obtained from the extraction of metal from its ore.
• It is a mixture of unwanted oxide and silicon dioxide CaSiO₃, FeSiO₃.
• It has a lower melting point and is not miscible with the molten metal.

• The extraction of metals is often done using various methods, depending on the reactivity and nature of the metal: - 
• Mining: This is the exploration of natural resources where the metal is extracted directly from its mineral ores in the earth's crust.

1. Smelting: Following the mining process, the ore is cleaned, reduced, and melted to separate the metal.
2. Roasting or Calcination: In the case of ores like sulfides or carbonates, they are often initially roasted or calcined (heated in the absence of air) to decompose the ores into other compounds and release the metal.
3. Electrolysis: This is used for metals highly reactive than carbon like potassium, calcium, sodium etc and metals like copper and gold. In this process, an electric current is passed through an ionic compound in a liquid state or in solution, causing it to break up into its constituent elements.
4. Reduction using Carbon: For metals like iron, nickel, zinc, and tin that are less reactive than carbon, can be extracted by carbon reduction - a form of displacement reaction where carbon is used to displace the metal from the metal oxide.
5. Leaching: For metals like aluminium and copper can also be extracted from their ores using a leaching process, which involves using a chemical reaction or bacterial action to separate a metal from its ore.
6. Hydrometallurgy: This is a method where aqueous chemistry is used for the recovery of metals from ores, concentrates, and recycled or residual materials.
7. Bioleaching: This is another method that involves the use of bacteria to extract metals from their ores.

• After obtaining the crude metal, it is then refined by different methods like electrolysis, distillation, zone refining, etc to get the pure metal.

The correct answer is Option -2 FeSiO_{3 .}
Explanation - 

• The slag obtained during the extraction of copper pyrites, also known as chalcopyrite, is mainly composed of iron silicate (fayalite, Fe2SiO4), as well as other materials such as calcium silicates and leftover materials that weren't part of the original copper pyrites ore.
• These leftover materials will vary depending on the makeup of the original ore and the extraction process.
• During the roasting and smelting processes, impurities and unwanted elements end up forming the slag.
• The primary purpose of these steps is to remove sulfur, iron, and other impurities from the ore, leaving behind copper matte, which is then further refined to create pure copper.

Note -

• The exact composition of the slag can differ depending on the specific ore being used and the extraction processes involved.
• The slag will contain any materials that are non-copper and non-sulfur, plus the reagents added during the smelting process.

Additional information-

• Metallurgy is a process of extracting metal through various processes from their respective ores that directly or indirectly influence the physical and chemical activities involved in the production of metals.

Concept:

Electrolytic Refining

• Electrolytic refining is a process used to purify metals, where an electric current is passed through an electrolyte solution containing the metal ions.
• In this process, the impure metal is used as the anode, and pure metal is deposited at the cathode, effectively separating the impurities from the metal.

Explanation:

• Anode: This is correct. In electrolytic refining, the impure metal is made the anode. At the anode, the impure metal dissolves into the electrolyte as metal ions, and impurities (such as slag and other non-metallic substances) either remain at the anode or settle out of the solution.
• Cathode: This is incorrect. The cathode is where pure metal is deposited during electrolytic refining. The cathode is made of a material like pure metal, where the metal ions from the anode are reduced to solid metal.
• Electrolyte: This is incorrect. The electrolyte is a solution containing metal salts or metal ions and is used to facilitate the transfer of metal ions between the anode and cathode.
• Catalyst: This is incorrect. A catalyst is a substance that speeds up a chemical reaction without being consumed in the process. It is not used in electrolytic refining.

Since the impure metal is made the anode in electrolytic refining, the correct answer is: Anode.