Q.What is the function of limestone in the extraction of iron? Give equation to explain its action.
🔒You're viewing a preview — the full solution, concept, methods & PYQ mapping are locked.
🔒 Start your 14-day free trial to unlock the full solution →Concept understanding — Extraction of Metals - Metallurgy
Metallurgy is the commercial extraction of a metal from its ore, chosen from three broad methods depending on the metal and ore involved: pyrometallurgy (reducing the ore to metal at high temperature using carbon, hydrogen or aluminium), hydrometallurgy (reducing the metal from an aqueous solution of its salt using a suitable reducing agent), and electrometallurgy (extracting the metal by electrolytic reduction of its molten compound). Whichever reduction method is eventually used, the general process runs through four broad stages: concentration (removing gangue -- unwanted sand, mud and other impurities -- from the mined ore, via washing, hydraulic classification, magnetic separation or froth flotation, depending on the ore's nature); roasting/calcination (heating the concentrated ore, typically converting it toward its oxide form and driving off volatile impurities); reduction/smelting (reducing the oxide to the free metal, often with an added flux to combine with any remaini …
Iron ore's acidic silica impurity does not melt at furnace temperature on its own, so limestone is added specifically to convert it into a removable slag through two linked reactions. …
Limestone (CaCO3) added to the blast furnace acts as a flux: it decomposes to CaO, which reacts with the silica (SiO2) gangue to form molten slag (CaSiO3) that separates from the liquid iron.
Iron ore usually contains silica (SiO2) as an acidic impurity that would not melt at the furnace temperature on its own. Limestone is added along with the ore and coke for exactly this reason:
Step 1 - Decomposition of limestone (in the hotter, lower part of the furnace):
CaCO3 -> CaO + CO2
Step 2 - The basic CaO formed reacts with the acidic SiO2 impurity to form calcium silicate (slag):
CaO + SiO2 -> CaSiO3 (slag)
…
Showing the 12 most recent of 13 on this concept.
- CBSE 2023Set ANNUAL1 markMCQQ.The impurities present in the ore is called -(a) Slag(b) Flux(c) Gangue(d) None of these
›Reveal solutionSolution
The earthy/rocky impurities present in an ore are called gangue.
Gangue refers to the unwanted silicious/earthy impurities (like sand, clay) associated with the ore in nature. Flux is a substance added deliberately during smelting to combine with the gangue and form a fusible slag; slag is the fusible product so formed (flux + …
- CBSE 2023Set ANNUAL1 markMCQQ.Leaching is a process for(a) reduction(b) concentration(c) refining(d) oxidation
›Reveal solutionSolution
Leaching selectively dissolves the wanted mineral from the gangue using a suitable reagent, which is a step of ore concentration, not reduction/refining/oxidation.
In leaching, the ore is treated with a suitable chemical reagent that dissolves the desired metal compound while leaving impurities (gangue) undissolved (or vice versa); the metal compound is then recovered from the solution. Classic example: bauxite (impure Al2O3) is concentrated by leaching with hot …
- CBSE 2023Set ANNUAL1 markMCQQ.Which of the following processes is used for purification of nickel?(a) Zone refining(b) Mond's process(c) Van Arkel process(d) Froth floatation process
›Reveal solutionSolution
Mond's process purifies nickel via a volatile carbonyl intermediate that is later thermally decomposed.
In Mond's process, impure nickel is heated in a stream of carbon monoxide to form volatile nickel tetracarbonyl, Ni(CO)4:
Ni + 4CO -> Ni(CO)4
This volatile compound is then decomposed at a higher temperature to deposit pure nickel:
Ni(CO)4 -> Ni + 4CO …
- CBSE 2023Set ANNUAL1 markQ.What is pyrometallurgy ?
›Reveal solutionSolution
Pyrometallurgy is high-temperature extraction of a metal, usually by reducing its oxide with heat and a reducing agent such as carbon.
Pyrometallurgy is the branch of metallurgy in which the concentrated ore (often first converted to its oxide by roasting/calcination) is heated to a high temperature, generally in the presence of a suitable reducing agent (such as carbon, carbon monoxide, or a more reactive metal), to reduce it to the free metal.
Examples:
- Reduction of iron oxide by coke (carbon) in a blast furnace: Fe2O3+3CO→2Fe+3CO2
- Reduction of ZnO by carbon: ZnO+C→Zn+CO
- Self-reduction (auto-reduction) of some sulphide ores, e.g. in copper extraction, where the ore itself supplies both oxidised and reduced sulphur/copper species that react together on heating. …
- CBSE 2023Set ANNUAL1 markQ.Write the chemical composition of cryolite.
›Reveal solutionSolution
Cryolite, used as a flux in the electrolytic extraction of aluminium, is Na3AlF6.
Cryolite has the chemical composition Na3AlF6 (sodium hexafluoroaluminate, also written 3NaF⋅AlF3). It is mixed with alumina in the Hall–Héroult electrolytic ce …
- CBSE 2022Set HE2181 markQ.Match the pairs correctly. Column A item:(ii) Slag. Column B options:(a) XeF4(b) C6H12O6(c) RNH2(d) CO(e) CaSiO3(f) H2SO4(g) Amorphous solid(h) C2H5OH. Find the correct match for 'Slag' from column B.
›Reveal solutionSolution
Slag is calcium silicate, CaSiO3, formed when the basic flux (CaO, from limestone) reacts with the acidic impurity SiO2 (gangue) in the blast furnace.
During the extraction of iron in the blast furnace, limestone (CaCO3) is added as a flux. It decomposes on heating: CaCO3 -> CaO + CO2. The resulting basic oxide CaO then combines with the acidic gangue (mainly silica, SiO2) present in the ore:
CaO + SiO2 -> CaSiO3 (slag) …
- CBSE 2022Set ANNUAL1 markQ.Name the ore from which aluminium is extracted. Write its composition.
›Reveal solutionSolution
The principal ore of aluminium is bauxite, a hydrated form of aluminium oxide.
Aluminium occurs in nature chiefly as its hydrated oxide. The ore used industrially (in the Bayer/Hall–Héroult process) for extracting aluminium is bauxite.
…
- CBSE 2020Set ANNUAL1 markQ.What is electrometallurgy?
›Reveal solutionSolution
Electrometallurgy is metal extraction/purification by passing electricity through a molten or dissolved metal compound.
Electrometallurgy is the method of extraction (or purification) of a metal by electrolysis of its fused salt or oxide, or of a solution of its salt. It is used for highly electropositive metals whose ions are very difficult to reduce chemically — for example, sodium is obtained by electrolysis of fused NaCl (Down's process), aluminium by electrolysis of fused Al2O3 dissolved in cryolite (Hall–Héroult …
- CBSE 2019Set ANNUAL1 markQ.When copper is extracted from pyrite ore, the molten copper metal in the Bassemer converter is contaminated with basic FeO impurity. Suggest a flux that can be used to remove the impurity as slag.
›Reveal solutionSolution
Since the impurity (FeO) is basic, an acidic flux (silica) is needed to convert it into a removable slag.
Fluxes are chosen to be chemically opposite to the impurity they must remove, so that they combine to form a low-melting, easily-separable slag. Since the impurity here, FeO, is a basic oxide, an acidic flux, silica (SiO2), is added to the Bessemer converter. It reacts with FeO to form fusible iron(II) silicate slag, which s …
- CBSE 2019Set ANNUAL1 markMCQQ.In Van Arkel method for refining zirconium or titanium, the halogen used is ______.(a) fluorine(b) chlorine(c) bromine(d) iodine
›Reveal solutionSolution
The Van Arkel (iodide) method refines Ti/Zr by forming the volatile metal tetraiodide and decomposing it on a hot filament, depositing pure metal.
In the Van Arkel–de Boer process, impure zirconium or titanium metal is heated with iodine vapour in an evacuated vessel to form the volatile tetraiodide, Zr+2I2ΔZrI4 (similarly TiI4). The volatile iodide is then decomposed on a white-hot tungsten filament (~1800 K), depositing highly pure metal and releasing iodine, whic …
- CBSE 2017Set ANNUAL1 markMCQQ.Common impurities present in Bauxite ore:(a) CuO(b) ZnO(c) Fe2O3(d) None of these
›Reveal solutionSolution
The chief ore of aluminium, bauxite, is typically contaminated with iron oxide (Fe₂O₃) along with silica and titanium oxide.
Bauxite is essentially hydrated aluminium oxide, Al2O3⋅xH2O. Naturally occurring bauxite deposits are impure and commonly contain:
- Fe₂O₃ (iron(III) oxide) — the most characteristic impurity, giving bauxite its reddish-brown colour
- SiO₂ (silica)
- TiO₂ (titanium dioxide) …
- CBSE 2017Set ANNUAL1 markMCQQ.In the metallurgy of iron from haematite, limestone is added to act as(a) flux(b) slag(c) a reducing agent(d) an oxidising agent.
›Reveal solutionSolution
Limestone decomposes to lime, which combines with silica impurity to form a fusible slag — limestone's role is that of a flux.
In the blast furnace extraction of iron from haematite, limestone (CaCO3) is added along with coke and ore. On heating, it decomposes to lime and CO2: CaCO3→CaO+CO2. The lime formed then combines with the silica (sand, SiO2) impurity present in the ore to form calcium silicate (CaSiO3), which is the slag — a fusible, low-melting compound that separates from the molten iron. Since limestone's ro …
🎓Unlock everything free for 14 days
- ✓Full step-by-step solutions
- ✓Concept-first explanations
- ✓Methods, shortcuts & mistakes
- ✓PYQ mapping + timed mock tests
Full access for 14 days. No credit card required.