Every Book Back multiple-choice question from Metallurgy (12th Standard Chemistry, Samacheer Kalvi) — each with the correct option highlighted and a clear, worked explanation. Free to read in English and Tamil.
Q1
Bauxite has the composition
- A. \(Al_{2}O_{3}\)
- B. \(Al_{2}O_{3}.nH_{2}O\)Correct
- C. \(Fe_{2}O_{3}.2H_{2}O\)
- D. None of these
Explanation. Bauxite is the primary ore used for extracting aluminium. Chemically, it consists of hydrated aluminium oxide, which is represented by the formula \(Al_{2}O_{3}.nH_{2}O\).
Q2
Roasting of sulphide ore gives the gas (A). (A) is a colourless gas. Aqueous solution of (A) is acidic. The gas (A) is
- A. \(CO_{2}\)
- B. \(SO_{3}\)
- C. \(SO_{2}\)Correct
- D. \(H_{2}S\)
Explanation. When sulphide ores are roasted in the presence of oxygen, they release sulphur dioxide gas. This gas is colourless and forms an acidic solution when dissolved in water.
Q3
Which one of the following reaction represents calcinations?
- A. \(2Zn + O_{2} \rightarrow 2ZnO\)
- B. \(2ZnS + 3O_{2} \rightarrow 2ZnO + 2SO_{2}\)
- C. \(MgCO_{3} \rightarrow MgO + CO_{2}\)Correct
- D. Both (a) and (c)
Explanation. Calcination is the process of heating an ore in the absence or limited supply of air. It typically involves the thermal decomposition of carbonates into their respective metal oxides.
Q4
The metal oxide which cannot be reduced to metal by carbon is
- A. PbO
- B. \(Al_{2}O_{3}\)Correct
- C. ZnO
- D. FeO
Explanation. Aluminium is a highly reactive metal with a very strong affinity for oxygen. Carbon reduction is not thermodynamically feasible for aluminium oxide, requiring electrolytic methods instead.
Q5
Which of the metal is extracted by Hall-Heroult process?
- A. AlCorrect
- B. Ni
- C. Cu
- D. Zn
Explanation. The Hall-Heroult process is the standard industrial method for extracting aluminium. It involves the electrolysis of alumina dissolved in a molten mixture of cryolite.
Q6
Which of the following statements, about the advantage of roasting of sulphide ore before reduction is not true?
- A. \(\Delta G_{f}^{0}\) of sulphide is greater than those for \(CS_{2}\) and \(H_{2}S\).
- B. \(\Delta G_{r}^{0}\) is negative for roasting of sulphide ore to oxide
- C. Roasting of the sulphide to its oxide is thermodynamically feasible.
- D. Carbon and hydrogen are suitable reducing agents for metal sulphides.Correct
Explanation. Carbon and hydrogen are not effective reducing agents for metal sulphides because metal sulphides are generally more stable than the sulphides of carbon or hydrogen.
Q7
Match items in column - I with the items of column – II and assign the correct code.
Column-I:
A) Cyanide process
B) Froth floatation process
C) Electrolytic reduction
D) Zone refining
Column-II:
(i) Ultrapure Ge
(ii) Dressing of ZnS
(iii) Extraction of Al
(iv) Extraction of Au
- A. A-(i), B-(ii), C-(iii), D-(iv)
- B. A-(iii), B-(iv), C-(v), D-(i)
- C. A-(iv), B-(ii), C-(iii), D-(i)Correct
- D. A-(ii), B-(iii), C-(i), D-(v)
Explanation. Cyanide leaching is used for gold extraction. Froth flotation is a concentration method for sulphide ores like ZnS. Electrolytic reduction extracts Al, and zone refining purifies germanium.
Q8
Wolframite ore is separated from tinstone by the process of
- A. Smelting
- B. Calcination
- C. Roasting
- D. Electromagnetic separationCorrect
Explanation. Tinstone is non-magnetic, whereas wolframite impurities possess magnetic properties. Therefore, electromagnetic separation is used to effectively remove wolframite from the tin ore.
Q9
Which one of the following is not feasible
- A. \(Zn(s) + Cu^{2+}(aq) \rightarrow Cu(s) + Zn^{2+}(aq)\)
- B. \(Cu(s) + Zn^{2+}(aq) \rightarrow Zn(s) + Cu^{2+}(aq)\)Correct
- C. \(Cu(s) + 2Ag^{+}(aq) \rightarrow 2Ag(s) + Cu^{2+}(aq)\)
- D. \(Fe(s) + Cu^{2+}(aq) \rightarrow Cu(s) + Fe^{2+}(aq)\)
Explanation. According to the reactivity series, copper is less reactive than zinc. Consequently, metallic copper cannot spontaneously displace zinc ions from an aqueous solution.
Q10
Electrochemical process is used to extract
- A. Iron
- B. Lead
- C. SodiumCorrect
- D. silver
Explanation. Active metals such as sodium are extremely reactive and cannot be reduced by conventional chemical reducing agents. They are extracted through the electrolysis of their fused salts.
Q11
Flux is a substance which is used to convert
- A. Mineral into silicate
- B. Infusible impurities to soluble impuritiesCorrect
- C. Soluble impurities to infusible impurities
- D. All of these
Explanation. A flux is a chemical substance added during smelting to react with infusible gangue present in the ore, converting it into a fusible material known as slag.
Q12
Which one of the following ores is best concentrated by froth – floatation method?
- A. Magnetite
- B. Haematite
- C. GalenaCorrect
- D. Cassiterite
Explanation. Froth flotation is a concentration technique specifically used for sulphide ores. Galena is lead sulphide (\(PbS\)), which makes it ideal for this concentration process.
Q13
In the extraction of aluminium from alumina by electrolysis, cryolite is added to
- A. Lower the melting point of aluminaCorrect
- B. Remove impurities from alumina
- C. Decrease the electrical conductivity
- D. Increase the rate of reduction
Explanation. Pure alumina has an extremely high melting point. Adding cryolite serves to significantly lower the melting temperature of the mixture and also improves its electrical conductivity.
Q14
Zinc is obtained from ZnO by
- A. Carbon reductionCorrect
- B. Reduction using silver
- C. Electrochemical process
- D. Acid leaching
Explanation. Zinc oxide is industrially reduced to metallic zinc by heating it with carbon (coke) in a reverberatory furnace through the process of smelting.
Q15
Extraction of gold and silver involves leaching with cyanide ion. silver is later recovered by
- A. Distillation
- B. Zone refining
- C. Displacement with zincCorrect
- D. liquation
Explanation. In the metallurgy of silver, the metal is first converted into a soluble cyanide complex. Silver is then recovered by adding zinc, which displaces the silver from the complex.
Q16
Considering Ellingham diagram, which of the following metals can be used to reduce alumina? (NEET-2018)
- A. Fe
- B. Cu
- C. MgCorrect
- D. Zn
Explanation. The feasibility of reduction is determined by comparing the relative positions of metal-metal oxide lines in the Ellingham diagram. A metal whose line is lower can reduce the oxide of a metal whose line is higher.
Q17
The following set of reactions are used in refining Zirconium
Zr (impure) + 2I\(_2\) \(\xrightarrow{523 K}\) ZrI\(_4\)
ZrI\(_4\) \(\xrightarrow{1800 K}\) Zr (pure) + 2I\(_2\)
This method is known as
- A. Liquation
- B. Van Arkel processCorrect
- C. Zone refining
- D. Mond’s process
Explanation. This chemical vapor transport method utilizes iodine to form a volatile zirconium tetraiodide which then decomposes on a hot tungsten filament. This specific refining technique is known as the Van Arkel process.
Q18
Which of the following is used for concentrating ore in metallurgy?
- A. Leaching
- B. Roasting
- C. Froth floatation
- D. Both (a) and (c)Correct
Explanation. Ore concentration involves removing impurities like gangue. Both chemical leaching and physical froth flotation are common methods used to increase the metal content percentage in an ore before further extraction steps.
Q19
The incorrect statement among the following is
- A. Nickel is refined by Mond’s process
- B. Titanium is refined by Van Arkel’s process
- C. Zinc blende is concentrated by froth floatation
- D. In the metallurgy of gold, the metal is leached with dilute sodium chloride solutionCorrect
Explanation. Gold extraction utilizes cyanide leaching, where gold forms a soluble complex with sodium cyanide in the presence of air. The statement incorrectly identifies sodium chloride as the leaching agent used in this metallurgical process.
Q20
In the electrolytic refining of copper, which one of the following is used as anode?
- A. Pure copper
- B. Impure copperCorrect
- C. Carbon rod
- D. Platinum electrode
Explanation. In an electrolytic cell for refining, the anode is made of the impure metal to be purified. As current flows, metal atoms oxidize and enter the electrolyte, effectively dissolving the anode into the solution.
Q21
Which of the following plot gives Ellingham diagram
- A. \(\Delta\)S Vs T
- B. \(\Delta\)G Vs TCorrect
- C. \(\Delta\)G Vs 1/T
- D. \(\Delta\)G Vs T\(^2\)
Explanation. Ellingham diagrams are constructed by plotting the standard Gibbs free energy of formation for oxides against the absolute temperature to evaluate the thermodynamic feasibility of reduction processes.
Q22
In the Ellingham diagram, for the formation of carbon monoxide
- A. \(\frac{\Delta S^0}{\Delta T}\) is negative
- B. \(\frac{\Delta G^0}{\Delta T}\) is positive
- C. \(\frac{\Delta G^0}{\Delta T}\) is negativeCorrect
- D. initially \(\frac{\Delta G^0}{\Delta T}\) is positive, after 700 \(^0\)C, \(\frac{\Delta G^0}{\Delta T}\) is negative
Explanation. The slope of a line in the Ellingham diagram is determined by the entropy change of the reaction. For carbon monoxide formation, an increase in gas moles results in a negative slope.
Q23
Which of the following reduction is not thermodynamically feasible?
- A. Cr\(_2\)O\(_3\) + 2Al \(\rightarrow\) Al\(_2\)O\(_3\) + 2Cr
- B. Al\(_2\)O\(_3\) + 2Cr \(\rightarrow\) Cr\(_2\)O\(_3\) + 2AlCorrect
- C. 3TiO\(_2\) + 4Al \(\rightarrow\) 2Al\(_2\)O\(_3\) + 3Ti
- D. none of these
Explanation. Aluminium has a higher affinity for oxygen compared to chromium, as evidenced by its more negative free energy of oxide formation. Therefore, chromium cannot spontaneously reduce alumina to aluminium metal.
Q24
Which of the following is not true with respect to Ellingham diagram?
- A. Free energy changes follow a straight line. Deviation occurs when there is a phase change.
- B. The graph for the formation of CO\(_2\) is a straight line almost parallel to free energy axis.Correct
- C. Negative slope of CO shows that it becomes more stable with increase in temperature.
- D. Positive slope of metal oxides shows that their stabilities decrease with increase in temperature.
Explanation. The orientation of a line in the Ellingham diagram is dictated by the entropy change. A nearly horizontal line signifies a reaction with zero entropy change, being parallel to the temperature axis.
