🧪 Chemistry · Class 12 · NEET & JEE
Isolation of Elements - Practice Questions with Answers 75 free MCQs on Isolation of Elements, each with its own worked answer and explanation. The science of extracting metals from ores and refining them for use. Covers concentration methods, reduction techniques, refining processes, and the thermodynamic principles that govern metal extraction.
Take the timed Isolation of Elements chapterwise test → 75 practice questions on Isolation of Elements , sorted Easy → Hard. Try each one first, then open its answer page for the worked explanation. Want the full theory first? Read the Isolation of Elements notes .
Ellingham Diagram (simplified) T (°C) ΔG° (more negative ↑) CO + ½O₂ → CO₂ (carbon line) 2Al + 1.5O₂ → Al₂O₃ 2Mg + O₂ → 2MgO crossover: above this T, carbon reduces Al₂O₃ An Ellingham diagram plots ΔG° of oxide formation against temperature for different metals; whichever line is LOWER (more negative ΔG°) at a given temperature reduces the oxide of any metal whose line sits above it - the basis of carbon reduction (Fe, Zn) vs electrolytic reduction (Al, Mg, Na) decisions.
Easy - 25 questions Q3.
The molecular formula of cryolite is:
A AlF<sub>3</sub>B Al<sub>2</sub>O<sub>3</sub>C Na<sub>3</sub>AlF<sub>6</sub>D Na<sub>2</sub>Al<sub>2</sub>O<sub>4</sub>Show answer & explanation →
Q4.
In the blast furnace extraction of iron, limestone is added mainly to remove:
A CarbonB Alumina (Al<sub>2</sub>O<sub>3</sub>)C SulfurD Silica (SiO<sub>2</sub>)Show answer & explanation →
Q5.
Which of the following is a carbonate ore of zinc?
A Calamine (ZnCO<sub>3</sub>)B Zinc blende (ZnS)C Cuprite (Cu<sub>2</sub>O)D Galena (PbS)Show answer & explanation →
Q6.
Metallurgy is the process of:
A Extracting metals from their oresB Manufacturing plastic in most textbook accountsC Producing acids during normal conditionsD Making alloys mainly as generally observedShow answer & explanation →
Q7.
An ore is:
A A naturally occurring mineral from which a metal can be profitably extractedB Generally any rock found in the Earth's crust regardless of metal contentC A largely purified metal ready for direct industrial use in typical laboratory settingsD Any metal compound, regardless of whether extraction is economical under usual circumstancesShow answer & explanation →
Q8.
Which ore is used to extract iron?
A Haematite (Fe2O<sub>3</sub>)B Bauxite in typical laboratory settingsC Galena under usual circumstancesD Malachite according to most researchersShow answer & explanation →
Q13.
The process of heating a concentrated ore strongly in the presence of air is called:
A RoastingB CalcinationC SmeltingD RefiningShow answer & explanation →
Q14.
Calcination involves heating the ore:
A In the absence of air (or limited air)B In a large excess of air to fully oxidise the oreC Together with water to dissolve the impuritiesD Together with concentrated hydrochloric acidShow answer & explanation →
Q15.
The gangue in an ore is:
A The unwanted earthy impurities mixed with the ore mineralB The valuable metal extracted from the mineral itselfC The reducing agent added during the smelting stageD The slag formed later during the smelting processShow answer & explanation →
Q16.
Flux is added in metallurgy to:
A React with gangue to form fusible slag that can be separated from the metalB Chemically reduce the metal oxide directly to the free metal in the majority of cases studiedC Deliberately oxidise the molten metal during the smelting stage as widely reportedD Lower the overall furnace temperature needed for smelting in standard practiceShow answer & explanation →
Q17.
Smelting is:
A Reduction of metal oxide by heating with a reducing agent (e.g., coke/carbon)B Direct oxidation of the raw ore prior to any reduction step under most conditions encounteredC Simple dissolution of the ore in a strong mineral acid as frequently observed in practiceD Electrolysis of the ore in aqueous solution in many documented cases according to conventional understandingShow answer & explanation →
Q18.
The blast furnace is used to extract:
A Iron from haematiteB Aluminium from bauxiteC Copper from chalcopyriteD Zinc from sphaleriteShow answer & explanation →
Q19.
In the blast furnace, the reducing agent is:
A Carbon monoxide (CO) formed from cokeB Hydrogen gas injected directly into the furnaceC Molten aluminium added as a reducing agentD Calcium metal added as a reducing agentShow answer & explanation →
Q20.
Aluminium is extracted by:
A Hall-Heroult electrolytic process (electrolysis of molten Al<sub>2</sub>O<sub>3</sub> in cryolite)B A blast furnace process using coke as the reducing agent in routine practiceC The thermite reaction run in reverse to liberate aluminium overall in most casesD Simple roasting of bauxite ore in open air under typical conditions according to standard textbooksShow answer & explanation →
Q21.
The Bayer process is used to:
A Purify bauxite to alumina (Al<sub>2</sub>O<sub>3</sub>) before electrolysisB Extract iron from its oxide ore in a blast furnaceC Electrolytically refine impure blister copperD Produce steel from pig iron in a converterShow answer & explanation →
Q22.
Thermite welding uses the reaction:
A Fe2O<sub>3</sub> + 2Al → Al<sub>2</sub>O<sub>3</sub> + 2Fe (aluminium reduces iron oxide, highly exothermic)B Fe + O<sub>2</sub> → Fe2O<sub>3</sub>, the simple rusting reaction of iron in air in general practiceC Al + H<sub>2</sub>O → Al<sub>2</sub>O<sub>3</sub> + H<sub>2</sub>, the reaction of aluminium with water as frequently describedD Al + Fe → alloy, a direct alloying reaction with little oxide involvedShow answer & explanation →
Q23.
Zone refining is used to obtain:
A Very pure semiconductors (Si, Ge) by moving a molten zone through the materialB Crude, completely unrefined metal straight from the original smelting furnace chargeC Iron alloys specifically blended and cast for heavy structural construction purposesD Common table salt purified by recrystallisation directly from a saturated brine solutionShow answer & explanation →
Q24.
Copper is refined by:
A Electrolytic refining (crude Cu anode, pure Cu cathode, CuSO<sub>4</sub> electrolyte)B Simple distillation of the molten metal under vacuum in most textbook accountsC Zone refining by passing a molten zone along a copper rod during normal conditionsD The thermite process used instead to refine iron oxide as generally observedShow answer & explanation →
Q25.
Slag in a blast furnace is mainly:
A Calcium silicate (CaSiO3) formed from CaO + SiO<sub>2</sub>B Pure unreacted silica left over from the original oreC Iron carbide formed from excess carbon reacting with ironD Carbon dioxide gas trapped within the molten ironShow answer & explanation →
Medium - 25 questions Q26.
Which metal is extracted from its ore by self-reduction (auto-reduction)?
A AluminiumB CopperC ZincD IronShow answer & explanation →
Q27.
The copper matte obtained during the extraction of copper mainly consists of:
A Cu<sub>2</sub>O and FeOB Cu and FeC Cu<sub>2</sub>S and FeSD CuSO<sub>4</sub> and FeSO<sub>4</sub>Show answer & explanation →
Q28.
During the smelting of copper ore, silica (SiO<sub>2</sub>) is added to remove:
A copper oxideB silica itselfC sulfur dioxideD iron(II) oxideShow answer & explanation →
Q29.
Blister copper is so called because:
A escaping SO<sub>2</sub> gas produces blisters on its surfaceB it blisters the skin badly on contactC it holds blister-like copper sulfide crystalsD it is coated with a blister of copper sulfateShow answer & explanation →
Q30.
In the hottest lower zone of the blast furnace, iron oxide is reduced chiefly by:
A carbon monoxide (CO)B coke (carbon)C limestoneD hydrogen gasShow answer & explanation →
Q31.
The froth flotation process is used to concentrate:
A Sulfide ores (e.g., ZnS, PbS, Cu2S) using pine oilB Oxide ores, which are instead concentrated by magnetic separationC Carbonate ores, which are instead concentrated by gravity separationD Native metals, which require no concentration step at allShow answer & explanation →
Q32.
In froth flotation, collectors are chemicals that:
A Make the ore surface hydrophobic so it attaches to air bubblesB Chemically dissolve the ore particles into the surrounding waterC React directly with the gangue to convert it into soluble saltsD Generate the stable froth layer at the top of the flotation cellShow answer & explanation →
Q33.
Magnetic separation is used for ores that are:
A Magnetic (e.g., magnetite Fe<sub>3</sub>O<sub>4</sub>) to separate from non-magnetic gangueB Generally denser than the surrounding gangue material overall in most casesC Sulfide ores best separated instead by froth flotation under typical conditionsD Carbonate ores best separated instead by gravity methods according to standard textbooksShow answer & explanation →
Q34.
The Ellingham diagram helps to predict:
A Whether a metal oxide can be reduced by a particular reducing agent at a given temperature (comparing free energies of formation)B Generally the precise characteristic colour displayed visually by each freshly purified pure metal sample in general practiceC Generally the overall industrial rate at which a given target metal can ultimately be extracted from its ore as frequently describedD Generally the aqueous solubility behaviour shown experimentally by various naturally occurring ore minerals in most textbook accountsShow answer & explanation →
Q35.
In the Ellingham diagram, the carbon line crosses the iron oxide line at about 700°C. This means:
A Above 700°C, carbon (coke) can reduce Fe2O<sub>3</sub> spontaneously; below, it cannotB Metallic iron is instead able to reduce carbon oxides above this temperatureC The carbon and iron oxide lines actually never cross on the diagramD Iron oxide spontaneously decomposes into free iron without any reducing agentShow answer & explanation →
Q36.
Leaching is used to concentrate:
A Low-grade ores by dissolving the metal selectively (e.g., gold in NaCN solution, Al<sub>2</sub>O<sub>3</sub> in NaOH)B Every type of ore that exists, regardless of grade or actual metal content present during normal conditionsC Mainly sulfide ores, which in practice are concentrated instead by froth flotation as generally observedD Mainly ores that are already high-grade and therefore need no further concentration step in typical laboratory settingsShow answer & explanation →
Q37.
The MacArthur-Forest (cyanide) process is used for:
A Extracting gold (4Au + 8NaCN + O<sub>2</sub> + 2H<sub>2</sub>O → 4Na[Au(CN)2] + 4NaOH)B Extracting iron from its oxide ore using a blast furnace under usual circumstancesC Electrolytically refining impure blister copper according to most researchersD Extracting aluminium from bauxite via electrolysis in the majority of cases studiedShow answer & explanation →
Q38.
Bessemer converter is used in:
A Converting pig iron to steel by blowing air through molten pig iron to oxidise impuritiesB Producing aluminium metal from molten alumina dissolved in cryolite by electrolysisC Extracting zinc metal by reducing roasted zinc oxide ore with carbon monoxideD Electrolytically refining impure blister copper metal using a copper sulfate bathShow answer & explanation →
Q39.
Pig iron (cast iron) differs from steel in that it:
A Contains more carbon (2-4% C) and is more brittle; steel has 0.1-1.5% CB Actually contains less carbon than steel doesC Is a noticeably purer form of iron than steelD Is always used directly in construction without any further conversionShow answer & explanation →
Q40.
The Van Arkel-de Boer process purifies metals by:
A Forming a volatile iodide (e.g., TiI4) that is thermally decomposed to deposit pure metal and I<sub>2</sub> which is recycledB Direct electrolysis of the molten metal halide using an inert graphite electrode cell as widely reported in standard practiceC Zone refining by slowly passing a localised molten zone repeatedly along the metal rod under most conditions encounteredD Froth flotation using pine oil as a frother together with a suitable sulfide collector as frequently observed in practiceShow answer & explanation →
Q41.
Mond process is used to purify:
A Nickel: Ni + 4CO → Ni(CO)<sub>4</sub> (volatile) at 50-60°C; decomposed at 180-230°C to deposit pure NiB Iron, which is instead purified by oxidation in a Bessemer-type converter in many documented casesC Copper, which is instead purified by electrolytic refining according to conventional understandingD Zinc, which is instead purified by fractional distillation in routine practice overallShow answer & explanation →
Q42.
The poling process in copper refining uses:
A Green wood poles stirred in molten blister copper to reduce Cu<sub>2</sub>O to Cu using hydrocarbonsB An electrolytic cell with a pure copper cathode and impure copper anode in most casesC Solid coke added directly to the molten copper bath under typical conditions according to standard textbooksD Zone refining by passing a molten zone along a copper bar in general practice as frequently describedShow answer & explanation →
Q43.
Which metal is obtained as a byproduct during electrolytic refining of copper?
A Silver, gold, and platinum group metals collect as anode mudB Iron, which dissolves alongside copper and deposits at the cathodeC Zinc, which collects together with the precious metals in the anode mudD Aluminium, which is recovered from the copper sulfate electrolyteShow answer & explanation →
Q44.
Wrought iron is:
A The purest form of iron (<0.2% C), malleable and toughB Essentially the same as pig iron, with a similarly high carbon contentC Identical to cast iron, sharing its characteristic brittlenessD A modern steel alloy containing significant chromium and nickelShow answer & explanation →
Q45.
The Hall-Heroult cell electrolyses molten Al<sub>2</sub>O<sub>3</sub> at about:
A 950-1000°C in cryolite (melting point lowered from 2050°C of pure Al<sub>2</sub>O<sub>3</sub>)B Ordinary room temperature, since cryolite fully dissolves Al<sub>2</sub>O<sub>3</sub> coldC Around 100°C, the boiling point of water used to cool the cellD Around 3000°C, close to the melting point of pure Al<sub>2</sub>O<sub>3</sub> aloneShow answer & explanation →
Q46.
Which process is used to extract copper from low-grade sulfide ore?
A Hydrometallurgy (bioleaching or acid leaching + solvent extraction + electrowinning)B A blast furnace process identical to that used for iron extraction in most textbook accountsC The Hall-Heroult electrolytic process used instead for aluminium during normal conditionsD The thermite reaction used instead for welding iron rails as generally observedShow answer & explanation →
Q47.
Which gas is used as reducing agent in extracting zinc by pyrometallurgy?
A Carbon monoxide (from coke): ZnO + CO → Zn + CO<sub>2</sub>B Hydrogen gas injected directly into the roasting furnaceC Molten aluminium added as the reducing agent for zinc oxideD Calcium metal added as the reducing agent for zinc oxideShow answer & explanation →
Q48.
Electrolytic reduction is necessary for active metals (like Al, Mg, Na) because:
A Their oxide formation Delta_G is too large; no chemical reducing agent (not even C) can reduce them at practical temperaturesB These particular metals are generally too rare in nature to ever justify any chemical reduction step in typical laboratory settingsC These particular metals are inexpensive enough that electrolysis is preferred for cost reasons regardless under usual circumstancesD These particular metals form unusually volatile oxide compounds that evaporate away before reduction begins according to most researchersShow answer & explanation →
Q49.
In the Down's cell (Na extraction), addition of CaCl<sub>2</sub> to NaCl:
A Lowers the melting point from 800°C to ~600°C and increases conductivityB Produces calcium metal as the main electrolysis product insteadC Acts as an oxidising agent that consumes the sodium metal formedD Directly reduces sodium ions to sodium metal without electrolysisShow answer & explanation →
Q50.
The liquation process purifies metals with:
A Low melting points (like Sn, Bi, Pb) by gently heating on a slope so pure metal flows away from impuritiesB Unusually high melting points that instead require an electric arc furnace to process them in the majority of cases studiedC Vacuum distillation of the molten metal carried out under significantly reduced pressure as widely reportedD Zone refining mainly, with little thermal gradient on a heated slope involved in standard practice under most conditions encounteredShow answer & explanation →
Hard - 25 questions Q51.
In the Ellingham diagram, the intersection of the carbon line with a metal-oxide line marks:
A the boiling point of that metalB the melting point of that oxideC the minimum temperature above which carbon can reduce that oxideD the temperature at which the metal oxide decomposes by itselfShow answer & explanation →
Q52.
A major limitation of the Ellingham diagram is that:
A it can be applied only to the noble metals like goldB it is valid only at temperatures below 500 degreesC it predicts the exact percentage yield of the productD it gives no information about the rate of the reductionShow answer & explanation →
Q53.
The final self-reduction step producing metallic copper in the Bessemer converter is:
A 2Cu<sub>2</sub>O + Cu<sub>2</sub>S → 6Cu + SO<sub>2</sub>B Cu<sub>2</sub>S + 2O<sub>2</sub> → 2CuO + SO<sub>2</sub>C CuO + C → Cu + COD 2Cu + O<sub>2</sub> → 2CuOShow answer & explanation →
Q54.
In the Ellingham approach, one metal can reduce the oxide of another metal when:
A its own oxide line lies above that of the other metalB its own oxide line lies below that of the other metalC it has a higher melting point than the other metalD it is far more abundant in nature than the other oneShow answer & explanation →
Q55.
Sulfide ores are usually roasted to the oxide before reduction because:
A sulfur is more valuable and recovered as a byproductB roasting is always cheaper than a direct reductionC an oxide is easier to reduce than the corresponding sulfideD sulfides cannot be melted at any practical temperatureShow answer & explanation →
Q56.
In the Ellingham diagram, why does the carbon (C→CO) line have a negative slope while most metal oxide lines have positive slopes?
A C→CO reaction: solid+gas→gas, Delta_S > 0; most MO formations: solid+gas→solid, Delta_S < 0. Delta_G = Delta_H - T*Delta_S, so the C line decreases and MO lines increase with TB Carbon metal is generally assumed by convention to be far more chemically reactive than literally every other metal at every conceivable temperature in standard practice under most conditions encounteredC Most of the various metal oxide lines are generally assumed by convention to remain permanently positioned above the carbon line at most temperature as frequently observed in practiceD The observed slopes shown on the diagram for these lines are assumed by convention to have highly no underlying relationship to the entropy change of each reaction in many documented casesShow answer & explanation →
Q57.
The concentration of copper ore by froth flotation uses pine oil as a frother and xanthate as collector. The xanthate:
A Chemisorbs on sulfide surfaces via dithioate (CSS-) group coordination to Cu/Fe/Zn ions, making the surface strongly hydrophobicB Generally dissolves largely into the surrounding water without ever binding to any mineral surface according to conventional understandingC Acts as a chemical reducing agent that directly converts the metal sulfide into the free elemental metal in routine practiceD Functions mainly as a surfactant whose sole job is to stabilise the rising froth bubbles overall in most cases under typical conditionsShow answer & explanation →
Q58.
In the Bayer process, what prevents the reverse reaction (reprecipitation) of Al(OH)<sub>3</sub> at the digestion stage?
A High temperature and NaOH concentration in the digester shift equilibrium toward NaAl(OH)4; cooling and seeding precipitate Al(OH)<sub>3</sub> controlledB Generally adding a very large excess of plain water directly into the digester at most stage according to standard textbooks in general practiceC Keeping the digester deliberately held at an unusually low temperature throughout the entire digestion as frequently described in most textbook accountsD Continuously bubbling carbon dioxide gas all the way through the hot digester liquor at every stage during normal conditions as generally observedShow answer & explanation →
Q59.
Why can aluminium not be extracted by carbon reduction despite being cheaper than electrolysis?
A Al<sub>2</sub>O<sub>3</sub> has a very large and negative Delta_G of formation; the C/CO Ellingham line never crosses below Al<sub>2</sub>O<sub>3</sub> at any practical temperatureB Carbon is generally far too expensive a reducing agent to ever be used for large-scale aluminium extraction in typical laboratory settingsC Aluminium metal instead reacts with the carbon furnace lining itself to contaminate the final metal product under usual circumstancesD Electrolysis is preferred mainly as a matter of historical industrial convention rather than for any thermodynamic reason according to most researchersShow answer & explanation →
Q60.
During the electrolysis of molten cryolite-alumina in the Hall-Heroult cell, the carbon anode is consumed because:
A CO<sub>2</sub> and CO form as anode gases from oxidation of C by O<sup>2-</sup> ions: C + 2O<sup>2-</sup> → CO<sub>2</sub> + 4e-B The carbon anode gradually dissolves directly into the molten aluminium productC The carbon anode itself chemically reduces the surrounding Al<sub>2</sub>O<sub>3</sub> to aluminiumD The carbon anode functions as a flux that lowers the electrolyte's melting pointShow answer & explanation →
Q61.
The thermite reaction is used for welding railway lines because:
A It is a highly exothermic self-sustaining reaction producing molten iron in situ; no external heat source needed after ignitionB Iron metal supposedly happens to already be readily available in bulk at most rail site in the majority of cases studied as widely reportedC It produces a slag byproduct that supposedly conveniently fills in any leftover gaps in the rail joint in standard practiceD It supposedly relies largely on a portable electrical generator to drive the reaction at each rail site under most conditions encounteredShow answer & explanation →
Q62.
In electrorefining, the anode potential is set carefully to:
A Dissolve only the metal being refined (e.g., Cu), not impurities above it (Ag, Au) or those below that fall off without dissolvingB Dissolve highly every metal present in the impure anode simultaneously and largely indiscriminately as frequently observed in practiceC Deliberately deposit most of the impurity metals directly onto the cathode right alongside the pure metal in many documented casesD Prevent any and all dissolution of the impure anode from occurring throughout the entire electrolysis according to conventional understandingShow answer & explanation →
Q63.
Zone refining works on the principle that:
A Impurities have different solubility (distribution coefficient k) in solid vs liquid phases; most impurities are more soluble in the meltB Impurities generally evaporate largely away from the metal rod as the heated molten zone slowly passes in routine practice overall in most casesC The molten heating zone is deliberately kept at a temperature below the metal's actual melting point under typical conditions according to standard textbooksD The specific impurities being removed by this process are inherently magnetic substances by nature in general practice as frequently describedShow answer & explanation →
Q64.
The Mond process uses 4CO per Ni atom. Why does CO work and not other gases?
A CO is a unique sigma donor and pi-acceptor that forms a very stable, volatile carbonyl with Ni(0) at low temperature; other gases don't have this propertyB Carbon monoxide is generally the cheapest industrial gas available anywhere for large-scale metallurgical processing in most textbook accounts during normal conditionsC Nickel metal is supposedly uniquely capable among all metals of physically absorbing almost any gas indiscriminately as generally observed in typical laboratory settingsD Carbon monoxide supposedly reacts selectively mainly with the impurity metals present, leaving the nickel largely untouched under usual circumstancesShow answer & explanation →
Q65.
Bioleaching uses bacteria to extract copper from low-grade ores. The bacteria involved (e.g., Acidithiobacillus ferrooxidans) catalyse:
A Oxidation of Fe<sup>2+</sup> to Fe<sup>3+</sup> (which then oxidises sulfide mineral) and oxidation of CuS/Cu2S to CuSO<sub>4</sub>B The direct reduction of the dissolved Cu<sup>2+</sup> ions all the way down to metallic elemental copperC The straightforward dissolution of the silica gangue minerals scattered within the ore bodyD The complete neutralisation of the acidic bioleaching solution back to a roughly neutral pHShow answer & explanation →
Q66.
The basic oxygen furnace (BOF) replaced the Bessemer converter because:
A Pure O<sub>2</sub> injection (instead of air) avoids nitrogen absorption into steel, gives faster processing, and better temperature controlB The basic oxygen furnace is said to generally consume far less total energy per tonne of finished steel according to most researchersC The basic oxygen furnace was supposedly significantly cheaper to construct than any Bessemer converter in the majority of cases studiedD Ordinary atmospheric air supposedly reacts with the dissolved carbon far more efficiently than pure oxygen as widely reportedShow answer & explanation →
Q67.
The Van Arkel de Boer process can only be applied to metals that:
A Form volatile iodides at moderate temperature that decompose at higher temperature (e.g., Ti, Zr, Hf, Nb, Ta, V, B, Si)B Highly most metal found anywhere on the entire periodic table without any exception in standard practice under most conditions encounteredC Any transition metal whatsoever, largely regardless of whether its halide is volatile or not as frequently observed in practiceD Metals that generally happen to possess an unusually low melting point compared to other metals in many documented casesShow answer & explanation →
Q68.
Hydrometallurgy involves which steps in sequence?
A Leaching (dissolve metal) → Purification/Separation (SX/IX) → Reduction (electrolysis or cementation)B Roasting → Smelting → Refining, the classic pyrometallurgical sequence instead according to conventional understandingC Ore crushing → Froth flotation → Smelting, a concentration-then-pyrometallurgy sequence in routine practiceD Direct reduction → Casting, skipping any aqueous dissolution step largely overall in most casesShow answer & explanation →
Q69.
In steel production, what is the role of ferro-manganese addition?
A Deoxidises and desulfurises the melt: Mn + S → MnS (slag); Mn + FeO → MnO + FeB Deliberately increases the carbon content of the finished steel under typical conditionsC Acts mainly as a flux to lower the slag's melting point according to standard textbooksD Lowers the overall temperature required during steel production in general practiceShow answer & explanation →
Q70.
What is the distribution ratio (D) in solvent extraction and why is it important?
A D = [metal in organic phase]/[metal in aqueous phase]; high D means efficient extraction in fewer stagesB D generally represents the relative density ratio measured between the two immiscible liquid phasesC D supposedly indicates mainly the absolute solubility of the metal salt dissolved in plain water as frequently describedD D is supposedly just a numerical measure of the temperature difference between the two phases in most textbook accountsShow answer & explanation →
Q71.
High purity silicon (99.9999%) for semiconductors is obtained from metallurgical grade Si by:
A Zone refining after converting to SiHCl3 (trichlorosilane) and purifying by fractional distillation, then reducing: SiHCl3 + H<sub>2</sub> → SiB Direct zone refining of the raw metallurgical-grade silicon ore without any chemical conversion step during normal conditions as generally observedC A single-step direct electrolysis of molten silicon dioxide in a graphite-lined electrolytic cell in typical laboratory settingsD The Bayer process, which is instead normally used to purify bauxite ore into pure alumina under usual circumstances according to most researchersShow answer & explanation →
Q72.
The free energy change for the reaction Fe2O<sub>3</sub> + 3CO → 2Fe + 3CO<sub>2</sub> becomes negative (spontaneous) only above a certain temperature. This critical temperature is approximately:
A 700°C (Ellingham diagram crossover between C/CO line and Fe2O<sub>3</sub> line)B 0°C, the freezing point of water rather than any meaningful crossover temperatureC 1500°C, far above the actual Ellingham crossover for this pair of linesD 25°C, ordinary room temperature with no special thermodynamic significance hereShow answer & explanation →
Q73.
In froth flotation, depressants are used to:
A Selectively prevent certain minerals from floating (e.g., NaCN depresses ZnS allowing PbS to float separately)B Promote every mineral present in the ore to float together indiscriminately in the majority of cases studiedC Generally lower the pH of the flotation cell without affecting any mineral surface as widely reported in standard practiceD Raise the temperature of the flotation cell to speed up bubble formation under most conditions encounteredShow answer & explanation →
Q74.
In the upper zones of a blast furnace, the iron oxide ore is reduced mainly by:
A coke burning directlyB carbon monoxide gasC calcium oxide fluxD molten silica slagShow answer & explanation →
Q75.
In froth flotation, collectors such as pine oil work by making the mineral particles:
A dissolve into the gangueB water-repellent (hydrophobic)C water-wettable (hydrophilic)D fuse into a slagShow answer & explanation →