Important MCQs on General Principles & Processes of Isolation of Elements

Ans. (D) Iron Pyrites

Explanation: Iron pyrite has the chemical formula FeS₂. It is cheaper to extract iron from other ores such as magnetite and hematite rather than exothermic iron pyrite since it creates a safety issue in mines. Pyrites can change into sulfurous minerals since they are often unstable.

Ans. (C) Argentite

Explanation: The only silver ore of the above options having the chemical formula Ag₂S is argentite, also known as a silver glance. Silver may be easily extracted from silver glance by smelting or chemical leaching.

Ans. (B) When the impurities can be distinguished from the ore by the naked eye

Explanation: When concentration is carried out by hand picking, it is crucial that impurities can be easily distinguished from ore particles. If these impurities are visible to the human eye, the ore is said to be pure. It is claimed that the ore is suitable for concentration by hand picking.

Ans. (C) Below the magnetic roller

Explanation: Over a conveyor belt that rotates around two rollers, one of which has an electromagnet, the powdered ore is dumped. When the ore particles travel across the belt, the magnetic roller draws the magnetic particles. Two piles therefore independently develop. Non-magnetic particles are collected away from the magnetic roller, while magnetic particles are gathered beneath it.

Ans. (C) Draws in the air causing frothing

Explanation: The froth flotation method produces foaming by vigorously stirring the collectors and froth stabilizers as well as the suspension of powdered ore in water.

Ans. (B) Hydrometallurgy

Explanation: In the field of extractive metallurgy, a method for removing metals from their ores is known as hydrometallurgy. Aqueous solutions are used in the hydrometallurgy process to extract metals from ores, concentrates, and recycled or residual materials.

Ans. (C) To remove volatile impurities in the form of their oxides

Explanation: Oxides that are volatile contaminants are removed from oxide ores by roasting. By reduction, it is simpler to get metals from their oxides than from carbonates or sulfides. As a result, before the ore can be reduced, it must first be converted to metal oxide.

Ans. Fe

Explanation: In fact, the correct reducing agent must be used to remove metal from its ore. Iron is a rather active metal, therefore carbon reduction rather than electrolysis can be used to decrease its oxides. Reactive metals like aluminium are recovered using electrolysis, whereas less reactive metals like iron are recovered using carbon reduction.

Ans. (C) Electrometallurgy

Explanation: With the use of electrometallurgy or electrolysis, sodium, a highly electropositive metal, is easily extracted from sodium chloride. Pyrometallurgy and hydrometallurgy are used to extract metals like copper, iron, and silver.

Ans. (D) Hall-Heroult process

Explanation: By using an electrochemical reaction, the Hall-Heroult method converts bauxite to almost pure aluminium. The bauxite is dissolved in sodium, fluorine, and aluminium electrolyte that is molten and maintained at a high temperature. In this procedure, oxygen gas is created at the anode while aluminium is deposited at the cathode.

Ans. (D) Greater solubility of the impurity in the molten state than in the solid.

Explanation: This approach is predicated on the idea that impurities are more soluble in the metal's melt than in its solid state. A rod made of impure metal has a circular mobile heater mounted to one end of it. The heater is moved forward while the molten zone follows. The pure metal separates from the melt as the heater advances, while the impurities are carried into the nearby molten zone.

Ans. (A) Flux

Explanation: A material known as flux can either be an acidic oxide (SiO₂) or a basic oxide (CaO, MgO). Slag is created when it mixes with certain impurities (gangue particles). This is simple to remove.

Ans. (B) their surface is not easily wetted by water.

Explanation: The difference in wettability between the ore and the gangue particles is the basis for the operation of the foam flotation process. Hydrophilic refers to particles that are easily wetted by water, whereas hydrophobic refers to particles that are not. In aqueous media, hydrophobic particles generally create a separate phase. 

In the froth flotation method, pine oil, a foaming agent, and sodium ethyl xanthate, a collecting agent, are both introduced to the water together with the powdered ore. The froth is stabilized by the addition of cresol and aniline. The mixture is stirred vigorously with air, causing the sulfide ore particles to adhere to the oil and rise to the surface as froth. However, water wets the gangue particles, which then sink to the tank bottom. So, using this procedure, the ores are purified.

Ans. (C) in presence of cryolite which forms a melt with a lower melting point.

Explanation: Pure aluminium is separated from its mixture using the Hall-Heroult technique. In this procedure, the melting point of the mixture is lowered while improving electrical conductivity by mixing pure aluminium (Al₂O₃) with calcium fluoride (CaF₂) or sodium aluminium hexafluoride (Na₃AlF₆). In the Hall-Heroult procedure, a steel tank with a graphite and carbon rod liner is employed.

Ans. (D) Both (a) and (b).

Explanation: Silver sulfide and sodium cyanide can react with each other again. Sodium sulfide is converted to sodium sulfate when air is passed across it. This stops the backward reaction.