(i) Why is blast furnace used in case of extraction of iron but not in case of extraction of zinc? (ii) What a

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Q. (i) Why is blast furnace used in case of extraction of iron but not in case of extraction of zinc?

(ii) What are the functions of sodium cyanide in case of extraction of silver from silver ore and cryolite in case of extraction of aluminium from alumina? [1+2] OR

(i) Write balanced chemical equations for the reactions involved in the extraction of copper from copper matte.

(ii) What is thermit mixture? [2+1]

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Zinc's low boiling point rules out blast-furnace extraction; NaCN and cryolite each serve as solvents/complexing agents that make their respective extractions feasible.

Blast furnace for iron but not zinc: Iron has a high melting point, so it can be reduced from its oxide by CO/coke at the high temperatures reached in a blast furnace and tapped off as molten metal. Zinc, however, has a comparatively low boiling point (~907°C) — at blast-furnace temperatures, zinc metal formed by reduction would immediately vaporise and be lost (or reoxidise) in the furnace gases before it could be collected as liquid metal. So zinc oxide is instead reduced with carbon in a retort/furnace designed for the vapour to be collected and condensed (distilled) separately.
Function of NaCN and cryolite:

NaCN in silver extraction: forms a soluble complex ion with silver via the cyanide (McArthur–Forrest) process — $4NaCN + Ag_2S \rightarrow 2Na[Ag(CN)_2] + Na_2S$ — leaching silver out of the ore into solution, from which it is later displaced by zinc.
Cryolite (Na $_3$ AlF $_6$ ) in aluminium extraction (Hall–Héroult process): acts as a flux/solvent that lowers the melting point of alumina (from ~2050°C to about 950°C) and increases the electrical conductivity of the molten mixture, making electrolysis economically feasible.

OR:

(i) Extraction of copper from copper matte:

$2Cu_2S + 3O_2 \rightarrow 2Cu_2O + 2SO_2$ …

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Same / Similar Concept — real previous-year questions on the same or a closely similar concept, not this exact question.

Showing the 12 most recent of 13 on this concept.

CBSE 2023Set ANNUAL1 markMCQ
$Q. The impurities present in the ore is called -$
(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 + …

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$Q. Leaching is a process for$
(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 …

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$Q. Which of the following processes is used for purification of nickel?$
(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 …

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$Q. What is pyrometallurgy ?$
›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: $Fe_2O_3 + 3CO \rightarrow 2Fe + 3CO_2$

Reduction of $ZnO$ by carbon: $ZnO + C \rightarrow Zn + CO$

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. …
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$Q. Write the chemical composition of cryolite.$
›Reveal solutionSolution

Cryolite, used as a flux in the electrolytic extraction of aluminium, is $Na_3AlF_6$ .

Cryolite has the chemical composition $Na_3AlF_6$ (sodium hexafluoroaluminate, also written $3NaF\cdot AlF_3$ ). It is mixed with alumina in the Hall–Héroult electrolytic ce …

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CBSE 2022Set HE2181 mark
$Q. Match the pairs correctly. Column A item:$
(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) …

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CBSE 2022Set ANNUAL1 mark
$Q. Name the ore from which aluminium is extracted. Write its composition.$
›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.

…

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CBSE 2020Set ANNUAL1 mark
$Q. What is electrometallurgy?$
›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 $Al_2O_3$ dissolved in cryolite (Hall–Héroult …

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CBSE 2019Set ANNUAL1 mark
$FeO$
›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 ( $SiO_2$ ), is added to the Bessemer converter. It reacts with $FeO$ to form fusible iron(II) silicate slag, which s …

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$Q. In Van Arkel method for refining zirconium or titanium, the halogen used is ______.$
(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, $Zr + 2I_2 \xrightarrow{\Delta} ZrI_4$ (similarly $TiI_4$ ). The volatile iodide is then decomposed on a white-hot tungsten filament (~1800 K), depositing highly pure metal and releasing iodine, whic …

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CBSE 2017Set ANNUAL1 markMCQ
$Q. Common impurities present in Bauxite ore:$
(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, $\text{Al}_2\text{O}_3\cdot x\text{H}_2\text{O}$ . 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) …
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$Q. In the metallurgy of iron from haematite, limestone is added to act as$
(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 ( $CaCO_3$ ) is added along with coke and ore. On heating, it decomposes to lime and $CO_2$ : $CaCO_3 \rightarrow CaO + CO_2$ . The lime formed then combines with the silica (sand, $SiO_2$ ) impurity present in the ore to form calcium silicate ( $CaSiO_3$ ), which is the slag — a fusible, low-melting compound that separates from the molten iron. Since limestone's ro …

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Q.(i) Why is blast furnace used in case of extraction of iron but not in case of extraction of zinc?

Concept understanding — Extraction of Metals - Metallurgy

Q.(i) Why is blast furnace used in case of extraction of iron but not in case of extraction of zinc?

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