15 extra multiple-choice questions for Metallurgy (12th Standard Chemistry, Samacheer Kalvi), beyond the ones printed in the textbook — each with the correct option highlighted and a clear, worked explanation. Free to read in English and Tamil.
Q1
Which of the following minerals is considered an ore of aluminium because extraction is commercially profitable?
- A. China clay
- B. BauxiteCorrect
- C. Kaolinite
- D. Malachite
Explanation. Bauxite is an ore of aluminium because it contains a high percentage of the metal and allows for convenient, economical extraction compared to other minerals like china clay.
Q2
In the gravity separation process, the separation of the ore from the gangue is primarily based on the difference in their:
- A. Magnetic properties
- B. Chemical reactivity
- C. Specific gravitiesCorrect
- D. Solubility in acids
Explanation. Gravity separation uses the difference in specific gravities between the heavy ore particles and the lighter gangue particles, which are washed away by a stream of running water.
Q3
What is the function of collectors like pine oil or eucalyptus oil in the froth floatation method?
- A. To decrease the wetting of ore particles by waterCorrect
- B. To increase the solubility of gangue
- C. To act as a stabilizing agent for the foam
- D. To prevent the oxidation of sulphide ores
Explanation. Collectors enhance the non-wettability of the mineral particles by water, making them attach to air bubbles and rise to the surface as froth.
Q4
During the extraction of silver by leaching, which reagent is typically used to dissolve the metal from its ore?
- A. Sodium hydroxide
- B. Dilute sulphuric acid
- C. Sodium cyanideCorrect
- D. Concentrated nitric acid
Explanation. Sodium cyanide is used in cyanide leaching to form a soluble complex with silver, which can then be recovered through a displacement reaction with zinc.
Q5
The process of roasting is most commonly applied for the conversion of which type of ores into their oxides?
- A. Carbonate ores
- B. Sulphide oresCorrect
- C. Silicate ores
- D. Halide ores
Explanation. Roasting involves heating the concentrated ore with excess oxygen below its melting point, which is standard for converting sulphide minerals into metal oxides.
Q6
Calcination differs from roasting primarily because it involves heating the ore in:
- A. The presence of excess oxygen
- B. A vacuum
- C. The absence of air or limited supply of airCorrect
- D. The presence of a reducing agent
Explanation. Calcination is the thermal treatment of an ore in the absence of air or limited air supply, used to remove water, organic matter, or carbon dioxide.
Q7
In the smelting of iron, quick lime (CaO) acts as a basic flux to remove silica gangue. The resulting product is:
- A. Elemental silicon
- B. Calcium silicate (slag)Correct
- C. Iron silicate
- D. Calcium carbide
Explanation. The basic flux CaO reacts with the acidic silica gangue (SiO2) to form an easily fusible calcium silicate, which is known as slag.
Q8
In an Ellingham diagram, the y-axis represents which thermodynamic property for the formation of metal oxides?
- A. Standard enthalpy change (\(\Delta H^0\))
- B. Standard entropy change (\(\Delta S^0\))
- C. Standard Gibbs free energy change (\(\Delta G^0\))Correct
- D. Equilibrium constant (K)
Explanation. The Ellingham diagram plots the standard Gibbs free energy change for the formation of various oxides against temperature to show relative stability.
Q9
Which reaction in the Ellingham diagram is represented by a line with a significant negative slope, making the product more stable at higher temperatures?
- A. \(C + O_2 \rightarrow CO_2\)
- B. \(2C + O_2 \rightarrow 2CO\)Correct
- C. \(2Mg + O_2 \rightarrow 2MgO\)
- D. \(4Al + 3O_2 \rightarrow 2Al_2O_3\)
Explanation. The formation of carbon monoxide from carbon and oxygen results in an increase in gas volume, increasing entropy. This leads to a negative slope in the \(\Delta G^0\) vs T plot.
Q10
Electrochemical principles are preferred for the extraction of highly active metals like sodium because:
- A. They have low melting points
- B. Their oxides are easily reduced by carbon
- C. Reduction by carbon is thermodynamically not feasibleCorrect
- D. They are only found as native elements
Explanation. Active metals have very stable oxides. The standard Gibbs free energy change for their reduction by carbon is positive, making chemical reduction non-spontaneous and necessitating electrolysis.
Q11
Which refining method is suitable for low boiling volatile metals like zinc and mercury?
- A. Liquation
- B. Zone refining
- C. DistillationCorrect
- D. Electrolytic refining
Explanation. Distillation is used for volatile metals. The impure metal is evaporated and the pure metal vapours are then condensed separately.
Q12
Zone refining is based on which of the following principles?
- A. Differences in magnetic attraction
- B. Impurities are more soluble in the melt than in the solid state of the metalCorrect
- C. Metals form volatile compounds with specific reagents
- D. Differences in standard reduction potentials
Explanation. Zone refining utilizes fractional crystallization. Impurities prefer to remain in the molten zone, which is slowly moved along the metal rod, concentrating them at one end.
Q13
In the Mond process for refining nickel, the metal is converted into which volatile compound?
- A. Nickel chloride
- B. Nickel tetracarbonylCorrect
- C. Nickel tetraiodide
- D. Nickel oxide
Explanation. Impure nickel reacts with carbon monoxide at around 350 K to form highly volatile \([Ni(CO)_4]\), which is then decomposed at higher temperatures to yield pure nickel.
Q14
The Van Arkel process for refining titanium and zirconium uses which reagent to form a volatile intermediate?
- A. Chlorine gas
- B. Carbon monoxide
- C. IodineCorrect
- D. Ammonia
Explanation. In the Van Arkel process, the impure metal is heated with iodine to form a volatile metal tetraiodide, which is subsequently decomposed on a tungsten filament.
Q15
Which alloy of iron is known for its high resistance to corrosion and is used in manufacturing surgical instruments and cutlery?
- A. Nickel steel
- B. Chrome steel
- C. Stainless steelCorrect
- D. Wrought iron
Explanation. Stainless steel is an important alloy of iron that resists corrosion, making it ideal for hospital equipment, cutlery, and jewellery.
