Q.How are metals found in nature?

Showing the 12 most recent of 13 on this concept.

1. 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 + gangue → slag) which is removed during metal extraction. So the impurity present in the ore itself is called gangue.

   ✓Final answer

   (c) Gangue

2. CBSE 2023Set ANNUAL1 markMCQ
   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 concentrated NaOH, which dissolves Al2O3 as sodium aluminate, leaving impurities like Fe2O3 behind. This is a concentration step, occurring before reduction and refining.

   ✓Final answer

   (b) concentration.

3. CBSE 2023Set ANNUAL1 markMCQ
   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

   (Zone refining is used for very-high-purity semiconductors like Si/Ge, Van Arkel process for Ti/Zr via iodides, froth flotation is an ore-concentration technique, not a refining method.)

   ✓Final answer

   (b) Mond's process.

4. CBSE 2023Set ANNUAL1 mark
   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.

   Pyrometallurgy is generally used for metals of moderate to high reactivity (e.g. Fe, Zn, Cu, Sn), as opposed to hydrometallurgy (aqueous leaching, e.g. Al, Au) or electrometallurgy (for highly reactive metals, e.g. Na, Mg, Al via electrolysis).

   ✓Final answer

   Pyrometallurgy is metal extraction by heating the ore/oxide to a high temperature with a reducing agent (e.g. carbon or CO) to obtain the free metal.

5. CBSE 2023Set ANNUAL1 mark
   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 cell to lower the melting point of the electrolyte and increase its electrical conductivity.

   ✓Final answer

   $Na_3AlF_6$

6. 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)

   Molten slag (calcium silicate) is less dense than molten iron, so it floats on top of the liquid metal inside the furnace and can be tapped off separately, removing the unwanted impurities.

   ✓Final answer

   (e) CaSiO3.

7. 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.

   Composition: $Al_2O_3.2H_2O$ (aluminium oxide with water of hydration), commonly contaminated with impurities such as $Fe_2O_3$ (giving the ore its red/brown colour), $TiO_2$, and $SiO_2$, which are removed by the Bayer process (digestion with hot NaOH solution, in which amphoteric $Al_2O_3$ dissolves as sodium aluminate while the impurities remain undissolved) before the purified alumina is electrolysed.

   ✓Final answer

   Bauxite — $Al_2O_3.2H_2O$ (hydrated aluminium oxide, with $Fe_2O_3$/$SiO_2$ as common impurities).

8. 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 process), and copper is refined electrolytically using impure copper as anode and pure copper as cathode in $CuSO_4$ solution.

   ✓Final answer

   Extraction/purification of a metal by electrolysis of its fused compound or salt solution.

9. CBSE 2019Set ANNUAL1 mark
   Q.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 ($SiO_2$), is added to the Bessemer converter. It reacts with $FeO$ to form fusible iron(II) silicate slag, which separates from the molten copper:

   $FeO + SiO_2 \rightarrow FeSiO_3\ (\text{slag})$

   ✓Final answer

   Silica ($SiO_2$), an acidic flux — it combines with basic $FeO$ to form fusible $FeSiO_3$ slag.

10. CBSE 2019Set ANNUAL1 markMCQ
    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, which is recycled: $ZrI_4 \xrightarrow{1800K} Zr + 2I_2$. Iodine is chosen because it forms a sufficiently volatile yet thermally decomposable halide with these metals, unlike the lighter halogens.

    ✓Final answer

    (d) iodine

11. 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)

    These impurities must be removed (e.g. via Bayer's process, which selectively dissolves Al₂O₃ in hot NaOH leaving Fe₂O₃ and other impurities as insoluble 'red mud') before the pure alumina can be electrolysed (Hall–Héroult process) to extract aluminium metal. CuO and ZnO are not characteristic bauxite impurities.

    ✓Final answer

    (c) Fe2O3

12. CBSE 2017Set ANNUAL1 markMCQ
    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 role here is to convert the infusible earthy impurity into a fusible slag, it is acting as a flux (the slag itself is the product, calcium silicate).

    ✓Final answer

    (a) flux — limestone converts silica impurity into fusible slag ($CaSiO_3$).