Isolation of Metals: JEE Advanced PYQ, 2007–2026

Q1 · Chemistry · Isolation of Metals

Tin, which melts at about 505 K, is refined by heating its impure form on a sloping hearth so that the molten tin flows away from infusible impurities. Which property of tin makes this separation possible?

• ATin has a lower melting point than the infusible impurities mixed with it.
• BTin is more reactive than its impurities, so the impurities are oxidised off.
• CTin has a higher boiling point than the impurities, so tin is distilled off as vapour.
• DTin has a lower density than the impurities, so the impurities sink to the bottom of the hearth.

Q2 · Chemistry · Isolation of Metals

97 g of pure ZnS (Zn = 65, S = 32, O = 16) is roasted in air at a moderate temperature. Incomplete control of conditions results in half of the zinc (by moles) ending up as ZnO (with loss of sulphur as SO2) and the other half as ZnSO4. What is the mass of the solid residue?

• A81 g
• B161 g
• C129 g
• D121 g

Q3 · Chemistry · Isolation of Metals

A finely powdered ore contains galena (PbS) and zinc blende (ZnS) together with siliceous gangue. It is concentrated by froth flotation using pine oil, and a small quantity of NaCN is added to the pulp. Which statement correctly describes the role of NaCN and the outcome?

• ANaCN acts as a collector for ZnS, so ZnS is carried into the froth along with PbS and the two sulphides are later separated from each other by gravity.
• BNaCN acts as a depressant: it forms a water-soluble zinc cyanide complex, Na2[Zn(CN)4], on the surface of ZnS, so ZnS is wetted by water and stays in the pulp, while PbS is carried up in the froth.
• CNaCN dissolves PbS as Na2[Pb(CN)4], so ZnS floats in the froth and the lead is recovered later from the solution.
• DNaCN is a froth stabiliser, like cresol or aniline, so it makes the froth more persistent and both sulphides rise together, separating them from the gangue only.

Q4 · Chemistry · Isolation of Metals

A 50 g sample of pure calcium carbonate, CaCO3 (Ca = 40, C = 12, O = 16), is heated strongly until decomposition is complete. What mass of CO2 gas is evolved?

• A22 g
• B44 g
• C28 g
• D50 g

Q5 · Chemistry · Isolation of Metals

Powdered bauxite (Al₂O₃·xH₂O containing Fe₂O₃, TiO₂ and SiO₂ as impurities) is digested with concentrated NaOH solution at 473–523 K and 35–36 bar. The solution is separated from the residue and CO₂ is passed through it. Which statement correctly describes the outcome?

• AFe₂O₃ dissolves as sodium ferrate and is carried into the filtrate, while Al₂O₃ is left behind in the residue, so CO₂ then precipitates iron(III) hydroxide.
• BAl₂O₃ dissolves as sodium aluminate, while SiO₂ stays undissolved in the residue along with Fe₂O₃ and TiO₂, so the filtrate contains only aluminate.
• CFe₂O₃ and TiO₂ remain in the residue, Al₂O₃ passes into solution as Na[Al(OH)₄], and CO₂ precipitates hydrated Al₂O₃ while sodium silicate stays in solution.
• DThe filtrate is treated with excess NaOH to precipitate Al(OH)₃, and CO₂ is used only to remove the dissolved silica.

Q6 · Chemistry · Isolation of Metals

Native gold (19.7 g, Au = 197) is leached from crushed ore using dilute aqueous NaCN with air bubbled through the mixture. All the gold dissolves as [Au(CN)2]⁻, and dissolved O2 is the only oxidant. The gold is then recovered completely from the solution by adding zinc dust, which is oxidised to [Zn(CN)4]²⁻. Taking Zn = 65, which option gives the amount of O2 consumed in the leaching step and the mass of Zn consumed in the precipitation step?

• A0.025 mol O2 and 3.25 g Zn
• B0.050 mol O2 and 3.25 g Zn
• C0.025 mol O2 and 6.5 g Zn
• D0.100 mol O2 and 6.5 g Zn

Q7 · Chemistry · Isolation of Metals

Which statement correctly distinguishes calcination from roasting in metallurgy?

• ACalcination is heating the ore in a limited supply of air, or in its absence, to decompose it; roasting is heating the ore in excess air, usually to oxidise sulphide ores.
• BCalcination is heating the ore in excess air to oxidise sulphides; roasting is heating in limited air to remove moisture.
• CBoth processes require the ore to be melted completely so that impurities separate as slag.
• DBoth processes are done only in the absence of air, because oxygen reduces the metal back to its element.

Q8 · Chemistry · Isolation of Metals

In the extraction of many metals, a sulphide ore is roasted to the oxide before being reduced with carbon, rather than reduced directly. Which statement gives the correct thermodynamic reason?

• AMost metal sulphides are more stable than CS2 and H2S (more negative ΔfG° per mole of sulphur), so C or H2 cannot reduce them directly. Roasting converts them to oxides, which carbon can reduce, and SO2 is evolved.
• BSulphides are less stable than CO2, so carbon would burn in the oxygen released before it could reduce the metal.
• CSulphides have much higher melting points than oxides, so they cannot be reduced in a furnace.
• DRoasting increases the oxidation state of the metal, and a metal in a higher oxidation state is always reduced more easily by carbon.

Q9 · Chemistry · Isolation of Metals

An ore concentrate is an equimolar mixture of calamine, ZnCO3, and zinc blende, ZnS. A 222 g sample is heated strongly in an excess of air until its mass is constant. The carbonate is calcined to ZnO and CO2, and the sulphide is roasted completely to ZnO and SO2. No ZnSO4 forms. (Zn = 65, S = 32, C = 12, O = 16) What percentage of the original mass is lost?

• A48.6%
• B27.0%
• C19.8%
• D7.2%

Q10 · Chemistry · Isolation of Metals

Which of the following is the role of a collector such as sodium ethyl xanthate in froth flotation?

• AIt adsorbs on the ore particles and makes their surface hydrophobic
• BIt makes the gangue surface hydrophobic so that it floats
• CIt dissolves the metal sulphide in water
• DIt generates the air bubbles used in the process