Daily Olympiad: Science - Metallurgy [20260702]

Solution

Correct: C

Froth flotation is a selective method primarily used for concentrating sulphide ores. In this process, the finely powdered ore is mixed with water and a frothing agent (like pine oil) and a collecting agent. Air is blown through the mixture, creating a froth that selectively carries the sulphide ore particles to the surface, while the gangue settles down. Gravity separation is for heavy oxide ores, magnetic separation for magnetic ores, and leaching for certain specific ores like bauxite or silver/gold ores.

Solution

Correct: B

Roasting is the process of heating a sulphide ore strongly in the presence of excess air below its melting point. This converts the sulphide ore into its corresponding metal oxide and releases sulphur dioxide gas. Calcination, on the other hand, involves heating a carbonate or hydrate ore strongly in the absence or limited supply of air to convert it into its oxide.

Solution

Correct: B

In the blast furnace, coke (carbon) reacts with oxygen to form carbon monoxide (CO), which is the primary reducing agent. Carbon monoxide then reduces iron oxides (Fe2O3) to metallic iron. Coke itself can also directly reduce iron oxide at higher temperatures. Limestone (CaCO3) acts as a flux to remove acidic impurities like silica, forming slag.

Solution

Correct: C

Highly reactive metals such as sodium, potassium, calcium, magnesium, and aluminium have a strong affinity for oxygen and cannot be reduced by carbon or carbon monoxide. They are typically extracted by the electrolytic reduction of their molten chlorides (e.g., NaCl) or oxides (e.g., Al2O3).

Solution

Correct: D

In electrolytic refining of copper, the impure copper is made the anode, and a thin sheet of pure copper is made the cathode. The electrolyte used is an acidic solution of copper sulphate. During electrolysis, copper from the anode dissolves and deposits on the cathode as pure copper. More reactive impurities from the anode also dissolve in the electrolyte but do not deposit on the cathode, while less reactive impurities (like gold, silver, platinum) do not dissolve and fall to the bottom as anode sludge.

Solution

Correct: C

Rusting is the corrosion of iron, specifically the formation of hydrated iron(III) oxide (Fe2O3.nH2O). This process requires the simultaneous presence of both oxygen (from the air) and water (moisture). The presence of salts or acids can accelerate the rusting process, but they are not fundamental requirements.

Solution

Correct: C

Galvanization is the process of applying a protective zinc coating to iron or steel to prevent rusting. Zinc acts as a sacrificial metal because it is more reactive than iron. Even if the zinc coating is scratched, the zinc will corrode preferentially to iron, thus protecting the underlying iron.

Solution

Correct: C

Alloys are homogenous mixtures of two or more metals, or a metal and a non-metal. They are made to enhance the desirable properties of metals. For instance, alloys can be harder, stronger, more resistant to corrosion, or have specific magnetic or electrical properties compared to their pure metallic components. While melting points can vary, the primary reason for alloying is property enhancement.

Solution

Correct: B

Bronze is an alloy primarily composed of copper, usually with tin as the main additive. Other modern additives include zinc, manganese, and aluminium. Brass is an alloy of copper and zinc. Solder is an alloy of lead and tin. Duralumin is an alloy of aluminium, copper, manganese, and magnesium.

Solution

Correct: C

Flux is a chemical substance added during smelting to remove non-metallic impurities (gangue) present in the ore. The flux reacts with the gangue to form a fusible product called slag, which is lighter than the molten metal and can be easily separated. For example, limestone (CaCO3) acts as a basic flux to remove acidic impurities like silica (SiO2) in the blast furnace.

Solution

Correct: C

Leaching is a chemical concentration method where the powdered ore is treated with a suitable chemical reagent that selectively dissolves the desired metal compound, leaving the impurities behind. This method is used for ores like bauxite (aluminium ore) where it's treated with concentrated NaOH solution, or for gold and silver ores using cyanide solutions. It relies on the chemical reactivity of the ore with a specific solvent.

Solution

Correct: B

The Thermite process utilizes aluminium powder as a reducing agent for the oxides of certain metals, particularly those metals which are less reactive than aluminium but cannot be easily reduced by carbon (e.g., chromium, manganese, iron). The reaction is highly exothermic, producing a molten metal and aluminium oxide. Aluminium, being more reactive than these metals, reduces their oxides. Sodium is extracted electrolytically, copper by its own oxide reduction, and zinc by carbon reduction.

Solution

Correct: B

Aluminium is a highly reactive metal, but it exhibits excellent corrosion resistance due to the formation of a very thin, dense, and tenacious layer of aluminium oxide (Al2O3) on its surface when exposed to air. This passive oxide layer prevents further oxidation of the underlying metal, effectively protecting it from corrosion. This process is often enhanced artificially through anodizing.

Solution

Correct: C

Amphoteric oxides are metal oxides that exhibit both acidic and basic properties, meaning they react with both acids and bases to form salts and water. Aluminium oxide (Al2O3) is a classic example of an amphoteric oxide. Copper oxide (CuO) and Magnesium oxide (MgO) are basic oxides, while Iron(III) oxide (Fe2O3) is generally considered basic.

Solution

Correct: C

In the electrolytic refining of copper, the impure copper forms the anode. As copper dissolves from the anode, more reactive metals also dissolve into the electrolyte. However, less reactive metals, such as gold, silver, and platinum, do not dissolve in the electrolyte and fall off the anode to collect at the bottom as 'anode sludge' (also called anode mud). This sludge is a valuable source of these precious metals.

Solution

Correct: D

Copper is widely used for making electrical wires due to its excellent electrical conductivity, ductility, and resistance to corrosion. While aluminium also has good conductivity and is lighter, copper generally offers better conductivity per unit volume and strength for most wiring applications.

Solution

Correct: C

Less reactive metals like mercury (from Cinnabar, HgS) and copper (from Copper glance, Cu2S) can be extracted by heating their sulphide ores in air. A part of the sulphide ore gets oxidized to its oxide, and then this oxide reacts with the remaining sulphide ore to produce the metal and sulphur dioxide. This process, where the ore reduces itself without an external reducing agent, is known as auto-reduction or self-reduction.

Solution

Correct: C

Magnetic separation is used when either the ore itself or the gangue associated with it is magnetic. For example, iron ores like haematite (Fe2O3) or magnetite (Fe3O4) can be separated from non-magnetic gangue, or a magnetic impurity like wolframite can be separated from non-magnetic tin stone (SnO2). The finely crushed ore passes over a magnetic roller, separating magnetic particles from non-magnetic ones.

Solution

Correct: C

Copper pyrites (CuFeS2) contain iron as an impurity. During smelting in a reverberatory furnace, the ore is roasted, converting some iron sulphide to iron oxide (FeO). Silica (SiO2) is then added as a flux, which reacts with the iron oxide to form fusible ferrous silicate (FeSiO3) slag. This slag, being lighter, floats on the molten copper matte and is easily skimmed off, thus removing the iron impurity.

Solution

Correct: C

Stainless steel is a family of iron-based alloys known for their excellent corrosion resistance. This property is primarily due to the addition of chromium (typically at least 10.5% by mass), which forms a passive, self-healing oxide layer on the surface. Nickel is also a common alloying element, especially in austenitic stainless steels, further enhancing corrosion resistance and mechanical properties.