Please refer to General Principles and Processes of Isolation of Elements Class 12 Chemistry Important Questions with answers below. These solved questions for Chapter 6 General Principles and Processes of Isolation of Elements in NCERT Book for Class 12 Chemistry have been prepared based on the latest syllabus and examination guidelines issued by CBSE, NCERT, and KVS. Students should learn these solved problems properly as these will help them to get better marks in your class tests and examinations. You will also be able to understand how to write answers properly. Revise these questions and answers regularly. We have provided Notes for Class 12 Chemistry for all chapters in your textbooks.

Important Questions Class 12 Chemistry Chapter 6 General Principles and Processes of Isolation of Elements

All General Principles and Processes of Isolation of Elements Class 12 Chemistry Important Questions provided below have been prepared by expert teachers of Standard 12 Chemistry. Please learn them and let us know if you have any questions.

Very Short Answer Questions :

Question. What is meant by the term ‘pyrometallurgy’?
Answer : The process of extraction of metal from its ore by heating the ore with a suitable reducing agent is known as pyrometallurgy.

Question. What are the collectors used in froth floatation process? Name a substance that can be used as such.
Answer : Collectors enhance non-wettability of the mineral particles. Pine oil can be used as collectors.

Question. What is the role of dilute NaCN in the extraction of gold? 
Answer : NaCN is used for leaching of gold ore in the presence of air to form soluble gold complex from which metal is displaced by adding more reactive metal.
4Au_(s) + 8CN^–_(aq) + 2H₂O_(l) + O_2(g) → 4[Au(CN)₂]^–_(aq) + 4OH^–_(aq)

Question. Describe the role of the following :
SiO₂ in the extraction of copper from copper matte
Answer : During the metallurgy of copper from copper pyrites, CuFeS₂, its roasting gives FeO besides Cu₂O and SO₂.

Question. Describe the principle controlling the following process :
Froth floatation method of concentration of a sulphide ore. 
Answer : The principle behind this method is that the sulphide ore is preferentially wetted by oils while gangue is preferentially wetted by water.
Then on agitation froth is formed that carries mineral particles and can be skimmed off.

Question. Describe the underlying principle of froth floatation process of concentration of ores.
Answer : The principle behind this method is that the sulphide ore is preferentially wetted by oils while gangue is preferentially wetted by water.
Then on agitation froth is formed that carries mineral particles and can be skimmed off

Question. Answer the following :
Differentiate between roasting and calcination.
Answer :

Question. Which form of the iron is the purest form of commercial iron? 
Answer : Wrought iron is the purest form of commercial iron.

Question. What is the composition of ‘copper matte’?
Answer : Cu₂S and FeS.

Question. What is the principle behind the zone refining of metals?
Answer : Zone refining is based on the principle that the impurities are more soluble in the melt than in the solid state of the metal.

Question. Why is electrolytic reduction preferred over chemical reduction for the isolation of certain metals?
Answer : Electropositive metals which cannot be reduced by chemical reduction are easily reduced electrolytically.

Question. Describe the underlying principle of recovery of silver from the solution obtained by leaching silver ore with a solution of NaCN.
Answer : During leaching Ag is oxidised to Ag⁺ which then combines with CN^– ions (from NaCN) to form soluble complex [Ag(CN)₂]^–. Silver is then recovered from this complex by displacement method using more electropositive zinc metal.
2[Ag(CN)₂]^–_(aq) + Zn_(s) → 2Ag_(s) + [Zn(CN)₄]^2–_(aq)

Question. Write the role of the following :
Iodine in the refining of zirconium.
Answer : In this method, crude metal is heated in an evacuated vessel with iodine. The metal iodide formed is decomposed on a tungsten filament at high temperature (1800 K) to get pure metal.
     Zr + 2I₂ → ZrI₄ → Zr + 2I²
    Impure                   Pure

Question. Name the method used for removing gangue from sulphide ores. 
Answer : Froth floatation method.

Question. Describe the following :
The role of carbon monoxide in the refining of crude nickel.
Answer : Titanium is refined by van Arkel method and nickel is refined by Mond’s process.

Question. What is meant by the term ‘chromatography’?
Answer : The term chromatography was derived from the Greek word “chroma”, meaning colour and “graphy”, for writing. It was used for the first time to separate the colour pigments of plants. Chromatography is a technique for analysing or separating mixtures of gases, liquids or dissolved substances.

Question. What is the role of CO₂ in the extractive metallurgy of aluminium from its ore?
Answer : The aluminate in solution is neutralised by passing CO₂ gas and hydrated Al₂O₃ is precipitated.
2Na[Al(OH)₄]_(aq) + CO_2(g) → Al₂O₃.xH₂O_(s) + 2NaHCO_3(aq).

Question. Describe the principle controlling the following process :
Preparation of cast iron from pig iron.
Answer : Pig iron is melted with scrap iron and coke using hot air blast. Due to this, impurities such as C, S and P present in the pig iron are removed as CO₂, SO₂ and P₂O₅ and carbon content is reduced to about 3%.

Question. What is the role of cryolite in the extraction of aluminium?
Answer : Purified alumina (Al₂O₃) is mixed with cryolite (Na₃AlF₆) which lowers the melting temperature of electrolyte and also increase its conductivity.

Question. Differentiate between a mineral and an ore.
Answer : The naturally occurring chemical substances present in the earth’s crust which can be obtained by mining are called minerals. Those minerals from which metals can be extracted economically are called ores.

Question. Copper matte is charged into a silica lined converter in extraction of copper. What is the role of silica lining here? 
Answer : The copper matte containing Cu₂S and FeS is put in silica lined converter. Some silica is also added and hot air blast is blown to convert remaining FeS to FeO, which is removed as slag with silica.

Question. Describe the underlying principle of the following process :
Vapour phase refining of metals.
Answer : Vapour phase refining : In this method, the metal is converted into its volatile compound and collected elsewhere. It is then decomposed to give pure metal. So, the two requirements are :
(a) The metal should form a volatile compound with an available reagent.
(b) The volatile compound should be easily decomposable, so that the recovery is easy.

Question. Which of the following ores can be concentrated by froth floatation method and why?
Fe₂O₃, ZnS, Al₂O₃
Answer : ZnS (Froth floatation method is used to remove gangue from sulphide ores).

Question. Describe the role of the following :
Silica in the extraction of copper from copper pyrites ore. 
Answer : During the metallurgy of copper from copper pyrites, CuFeS₂, its roasting gives FeO besides Cu₂O and SO₂.

Question. Which method is employed for extracting copper from low grade ores and scraps?
Answer : Copper is extracted by hydrometallurgy from low grade ores. It is leached out using acid or bacteria. The solution containing Cu²⁺ is treated with scrap iron or H₂.
          Cu²⁺_(aq) + H_2(g) → Cu_(s) + 2H⁺_(aq)

Question. What is the role of silica in the extraction of copper? 
Answer : During the metallurgy of copper from copper pyrites, CuFeS₂, its roasting gives FeO besides Cu₂O and SO₂.

Question. The reaction Cr₂O₃ + 2Al → Al₂O₃ + 2Cr ; ΔG° = – 421 kJ is thermodynamically feasible as is apparant from the Gibbs energy value. Why does it not take place at room temperature?
Answer : In solid state chance of contact between reactants is negligible.
Some thermodynamically feasible reactions also require some activation energy for initiation.
Hence, the reaction does not take place at room temperature.

Question. Write the reactions involved in the following process :
Leaching of bauxite ore to prepare pure alumina.
Answer : (i) Leaching of bauxite ore to prepare pure alumina : 

Short Answer Questions :

Question. How is chemical reduction different from electrolytic reduction? Name a metal each which is obtained by
(i) electrolytic reduction,
(ii) chemical reduction.
Answer : In chemical reduction, metal is obtained by reduction of its ore by a suitable reducing agent, whereas in electrolytic reduction, reduction is carried out by passing electric current through molten ore.
(i) Aluminium is obtained by electrolytic reduction.
(ii) Iron is obtained by chemical reduction.

Question. Outline the principles behind the refining of metals by the following methods :
(i) Zone refining method
(ii) Chromatographic method 
Answer : (i) Zinc is refined by electrolytic refining.
In this method, the impure metal is made to act as anode. A strip of the same metal in pure form is used as cathode. They are put in a suitable electrolytic bath containing soluble salt of the same metal. The more basic metal remains in the solution and the less basic ones go to the anode mud.
At anode : Zn → Zn²⁺ + 2e^–
At cathode : Zn²⁺ + 2e^– → Zn
(ii) Chromatographic method is based on the principle that different components of a mixture are differently adsorbed on an adsorbent. The adsorbed components are removed (eluted) by using suitable eluent. There are several chromatographic techniques such as paper chromatography, colum chromotagraphy, gas chromatography, etc.

Question. Define the following terms :
(i) Roasting
(ii) Calcination 
Answer : 

Question. How is wrought iron different from steel?
Answer : Wrought iron is the purest form of iron. Steel is an alloy of iron which contains requisite amount of C, Mn, Ni, Cr, etc.

Question. State the principle involved in refining of metals by each of the following methods :
(i) Zone refining
(ii) Vapour phase refining
(iii) Electrolytic refining
Answer : (i) Zinc is refined by electrolytic refining.
In this method, the impure metal is made to act as anode. A strip of the same metal in pure form is used as cathode. They are put in a suitable electrolytic bath containing soluble salt of the same metal. The more basic metal remains in the solution and the less basic ones go to the anode mud.
At anode : Zn → Zn²⁺ + 2e^–
At cathode : Zn²⁺ + 2e^– → Zn
(ii) Vapour phase refining : In this method, the metal is converted into its volatile compound and collected elsewhere. It is then decomposed to give pure metal. So, the two requirements are :
(a) The metal should form a volatile compound with an available reagent.
(b) The volatile compound should be easily decomposable, so that the recovery is easy.
(iii) Zone refining is based on the principle that the impurities are more soluble in the melt than in the solid state of the metal.

Question. Giving examples differentiate between calcination and roasting. 
Answer : 

Question. (i) What is the role of silica in the extraction of copper?
(ii) How is ‘cast iron’ different from ‘pig iron’?
Answer : (i) During the metallurgy of copper from copper pyrites, CuFeS₂, its roasting gives FeO besides Cu₂O and SO₂.

(ii) Impure iron obtained from blast furnace is known as pig iron and cast into pigs (blocks). It contains 4-5 percent of carbon along with some phosphorus, silicon, manganese and sulphur.
Cast iron contains a less percentage of carbon (1.8 to 3 percent) made by melting pig iron with scrap iron and coke using hot air blast.

Question. Describe the principle involved in each of the following processes.
(i) Mond process for refining of nickel.
(ii) Column chromatography for purification of rare elements. 
Answer : (i) Mond’s process : Impure nickel is treated with carbon monoxide at 60-80°C to form volatile nickel carbonyl which decomposes to give pure nickel at 180°C.
      Ni + 4CO → Ni(CO)₄ → Ni + 4CO
     Impure                         Pure
(ii) Chromatographic method is based on the principle that different components of a mixture are differently adsorbed on an adsorbent. The adsorbed components are removed (eluted) by using suitable eluent. There are several chromatographic techniques such as paper chromatography, colum chromotagraphy, gas chromatography, etc.

Question. Describe the principle involved in each of the following processes.
(i) Zone refining of a metal
(ii) Vapour phase refining of metals.
Answer : (i) Zone refining is based on the principle that the impurities are more soluble in the melt than in the solid state of the metal.
(ii) Vapour phase refining : In this method, the metal is converted into its volatile compound and collected elsewhere. It is then decomposed to give pure metal. So, the two requirements are :
(a) The metal should form a volatile compound with an available reagent.
(b) The volatile compound should be easily decomposable, so that the recovery is easy.

Question. Which methods are usually employed for purifying the following metals?
(i) Nickel (ii) Germanium
Mention the principle behind each one of them.
Answer : (i) Mond’s process : Impure nickel is treated with carbon monoxide at 60-80°C to form volatile nickel carbonyl which decomposes to give pure nickel at 180°C.
      Ni + 4CO → Ni(CO)₄ → Ni + 4CO
     Impure                         Pure
(ii) Zinc is refined by electrolytic refining.
In this method, the impure metal is made to act as anode. A strip of the same metal in pure form is used as cathode. They are put in a suitable electrolytic bath containing soluble salt of the same metal. The more basic metal remains in the solution and the less basic ones go to the anode mud.
At anode : Zn → Zn²⁺ + 2e^–
At cathode : Zn²⁺ + 2e^– → Zn

Question. Write the chemical reactions involved in the extraction of silver from silver ore.
Answer :

Question. Write down the reactions taking place in different zones in the blast furnace during the extraction of iron. How is pig iron different from cast iron?
Answer : Reduction of iron oxide in blast furnace :
(i) Lower zone of the blast furnace :
          C + O₂ → CO₂ + heat
          C + CO₂ → 2CO
Coke is burnt to give temperature up to 2200 K at lower part of the blast furnace.
(ii) Middle zone of the blast furnace : CO and heat move up in the furnace. The temperature range in the middle zone of the blast furnace is 900-1500 K.
         FeO + CO → Fe + CO₂
Lime stone is also decomposed to CaO which removes silicate impurity of the ore as slag.
         CaCO₃ →¹¹⁰⁰ K CaO + CO₂
         C + CO₂ → 2CO
         CaO + SiO₂ → CaSiO₃
                               Slag
(iii) Upper zone of the blast furnace : Temperature range in this zone is 500-800 K.
          3Fe₂O₃ + CO → 2Fe₃O₄ + CO₂
          Fe₃O₄ + 4CO → 3Fe + 4CO₂
          Fe₂O₃ + CO → 2FeO + CO₂
Impure iron obtained from blast furnace is known as pig iron and cast into pigs (blocks). It contains 4-5 percent of carbon along with some phosphorus, silicon, manganese and sulphur.
Cast iron contains a less percentage of carbon (1.8 to 3 percent) made by melting pig iron with scrap iron and coke using hot air blast.