CBSE Class 12 Chemistry General Principles and Processes of Isolation of Elements Worksheet Set A

Question. Which one is malachite from the following?
(a) CuCO₃.Cu(OH)₂
(b) CuFeS₂
(c) Cu(OH)₂
(d) Fe₃O₄ 
Answer. A

Question. Identify the incorrect statement.
(a) The scientific and technological process used for isolation of the metal from its ore is known as metallurgy.
(b) Minerals are naturally occurring chemical substances in the earth’s crust.
(c) Ores are minerals that may contain a metal.
(d) Gangue is an ore contaminated with undesired materials. 
Answer. D

Question. “Metals are usually not found as nitrates in their ores.” Out of the following two (I and II) reasons which is/are true for the above observation?
I. Metal nitrates are highly unstable.
II. Metal nitrates are highly soluble in water.
(a) I is false but II is true.
(b) I is true but II is false.
(c) I and II are true.
(d) I and II are false 
Answer. A

Question. Which one of the following is a mineral of iron?
(a) Malachite
(b) Cassiterite
(c) Pyrolusite
(d) Magnetite 
Answer. D

Question. Cassiterite is an ore of
(a) Sb
(b) Ni
(c) Mn
(d) Sn
Answer. D

Question. Sulphide ores of metals are usually concentrated by froth floatation process. Which one of the following sulphide ores offer an exception and is concentrated by chemical leaching?
(a) Galena
(b) Copper pyrite
(c) Sphalerite
(d) Argentite
Answer. D

Question. Roasting of sulphides gives the gas X as a byproduct.This is a colourless gas with choking smell of burnt sulphur and causes great damage to respiratory organs as a result of acid rain. Its aqueous solution is acidic, acts as a reducing agent and its acid has never been isolated. The gas X is
(a) CO₂
(b) SO₃
(c) H₂S
(d) SO₂ 
Answer. D

Question. Considering Ellingham diagram, which of the following metals can be used to reduce alumina?
(a) Fe
(b) Zn
(c) Mg
(d) Cu 
Answer. C

Question. In the extraction of copper from its sulphide ore, the metal is finally obtained by the reduction of cuprous oxide with
(a) carbon monoxide
(b) copper (I) sulphide
(c) sulphur dioxide
(d) iron (II) sulphide.
Answer. B

Question. The metal oxide which cannot be reduced to metal by carbon is
(a) Al₂O₃
(b) PbO
(c) ZnO
(d) Fe₂O₃
Answer. A

Question. Which of the following elements is present as the impurity to the maximum extent in the pig iron?
(a) Manganese
(b) Carbon
(c) Silicon
(d) Phosphorus
Answer. B

Question. The following reactions take place in the blast furnace in the preparation of impure iron. Identify the reaction pertaining to the formation of the slag.
(a) Fe₂O_3(s) + 3CO_(g) → 2Fe_(l) + 3CO_2(g)
(b) CaCO_3(s) → CaO_(s) + CO_2(g)
(c) CaO_(s) + SiO_2(s) → CaSiO_3(s)
(d) 2C_(s) + O_2(g) → 2CO_(g)
Answer. C

Question. Which of the following statements, about the advantage of roasting of sulphide ore before reduction is not true?
(a) The DGf° of the sulphide is greater than those for CS₂ and H₂S.
(b) The DGf° is negative for roasting of sulphide ore to oxide.
(c) Roasting of the sulphide to the oxide is thermodynamically feasible.
(d) Carbon and hydrogen are suitable reducing agents for metal sulphides. 
Answer. D

Question. Nitriding is the process of surface hardening of steel by treating it in an atmosphere of
(a) NH₃
(b) O₃
(c) N₂
(d) H₂S 
Answer. A

Question. Aluminium is extracted from alumina (Al₂O₃) by electrolysis of a molten mixture of
(a) Al₂O₃ + HF + NaAlF₄
(b) Al₂O₃ + CaF₂ + NaAlF₄
(c) Al₂O₃ + Na₃AlF₆ + CaF₂
(d) Al₂O₃ + KF + Na₃AlF₆
Answer. C

Question. Purification of aluminium, by electrolytic refining, is known as
(a) Hoope’s process
(b) Baeyer’s process
(c) Hall’s process
(d) Serpeck’s process.
Answer. A

Question. Calcium is obtained by
(a) reduction of calcium chloride with carbon
(b) electrolysis of molten anhydrous calcium chloride
(c) roasting of limestone
(d) electrolysis of solution of calcium chloride in H₂O. 
Answer. B

Question. Extraction of gold and silver involves leaching with CN– ion. Silver is later recovered by
(a) distillation
(b) zone refining
(c) displacement with Zn
(d) liquation. 
Answer. C

Question. Identify the correct statement from the following :
(a) Wrought iron is impure iron with 4% carbon.
(b) Blister copper has blistered appearance due to evolution of CO₂.
(c) Vapour phase refining is carried out for Nickel by van Arkel method.
(d) Pig iron can be moulded into a variety of shapes.
Answer. D

Question. Match items of Column I with the items of Column II and assign the correct code :
       Column I                     Column II
(A) Cyanide process         (i) Ultrapure Ge
(B) Froth floatation          (ii) Dressing of ZnS
process
(C) Electrolytic               (iii) Extraction of Al
reduction
(D) Zone refining           (iv) Extraction of Au
(v) Purification of Ni
Code :
       A   B   C   D
(a) (i) (ii) (iii) (iv)
(b) (iii) (iv) (v) (i)
(c) (iv) (ii) (iii) (i)
(d) (ii) (iii) (i) (v) 
Answer. C

Question. Which of the following pairs of metals is purified by van Arkel method?
(a) Ga and In
(b) Zr and Ti
(c) Ag and Au
(d) Ni and Fe
Answer. B

Question. The method of zone refining of metals is based on the principle of
(a) greater mobility of the pure metal than that of the impurity
(b) higher melting point of the impurity than that of the pure metal
(c) greater noble character of the solid metal than that of the impurity
(d) greater solubility of the impurity in the molten state than in the solid.
Answer. D

 Very Short Answer

Question. What is gangue? 
Answer. An ore is usually a contaminated with the earthly or undesired materials is called gangue.

Question. Define metallurgy? 
Answer. The entire scientific and technological process used for isolation of the metal from its ore is called metallurgy.

Question. Define blister copper? 
Answer. The solidified copper obtained has blistered appearance due to the evolution of SO2, it is called blister copper.

Question. What is concentration? 
Answer. Removal of the unwanted materials from the ore is called concentration.

Question. What are the different types of the concentration of ores? 
Answer. Hydraulic washing, magnetic separation and forth floatation method are the different types of the concentration of ores.

Short Answer

Question. What are the major steps of extraction and isolation of metals? 
Answer. The major steps for extraction and isolation of metals from ores are:
1. Concentration of the ore.
2. Isolation of the metal from its concentrated ore.
3. Purification of the metal.

Question. Distinguish between minerals and ores? 
Answer. 1. Minerals are natural occurring chemical substances obtained from earth crust by mining whereas ores are those minerals from which the metals can be extracted profitably and conveniently.
2. All minerals are not ores whereas all ores are minerals.

Question. What is the principle of forth floatation method? 
Answer. Froth floatation process is based on the principle that the metallic sulphide particles of ore are preferentially wetted by oil and the gangue particles by water. Collectors attach themselves by polar groups to grains of minerals which then become water repellent and thus, pass on into the froth.

Question. What do you understand by Hall-Heroult process? 
Answer. The Hall–Heroult process is the major industrial process for smelting aluminium. It involves dissolving aluminium oxide i.e., alumina, obtained it most often from bauxite, aluminium's chief ore, through the Bayer process in molten cryolite, and electrolysing the molten salt bath, typically in a purpose-built cell.

Question. What do you mean by the magnetic separation? 
Answer. Magnetic separation is the process of separating components of mixtures by using magnets to attract magnetic materials. The process that is used for magnetic separation detaches non-magnetic material with those who are magnetic. The main purpose of magnetic separation is to recover or remove particles with sizes ranging from several tens of millimetres down to a fraction of micrometre, with a wide spectrum of magnetic susceptibilities, from ferromagnetic to diamagnetic

Long Answer

Question. Explain Ellingham diagram? 
Answer. An Ellingham diagram is a graph showing the temperature dependence of the stability of compounds. This analysis is usually used to evaluate the ease of reduction of metal oxides and sulphides. These diagrams were first constructed by Harold Ellingham in 1944. A line is drawn from the origin of the graph (T = 0, ΔG = 0) through the point on the Ellingham line of interest, at the required temperature. The equilibrium partial pressure is read off at the point where the drawn line crosses the monographic scale.
1. Ellingham diagram normally consists of plots of Δf GƟ vs T for the formation of the oxides of common metals and reducing the agents i.e., for the reaction.
2. Each plot is a straight line and slopes upwards except when some change in phase (s→ 1 or 1 →g) takes place. The temperature at which such change occurs. It is indicated by an increase in the slope on positive side.
3. When temperature is raised a point is reached in the curve where it crosses Δr GƟ = 0 lines, this temperature Δr GƟ for the formation of oxide is negative so the oxide is stable. Free energy of the formation of the oxide is positive. The oxide will decompose on its own.
4. Ellingham diagrams are constructed for the sulphides and the halides also.

Question. Explain electrochemical principles of metallurgy? 
Answer. The principles of metallurgy are effective in the reduction of metal ions to their respective metals in their solution or molten states. The reduction is carried out through electrolysis or using reducing elements. Such methods are based on the electrochemical principles.
Mn+ + A → M + An+
Metal ion reducing Element Metal Reduced ion
These electrochemical principles are explained in
ΔG° = -nE°F
n = Number of Electrons Gained
E° = Electrode Potential of Redox Couple
The value of E⁰ for a metal depends on its reactivity. Thus, it differs from metal to metal.
More reactive metals have high E⁰, whereas less reactive metals have low E0. It is difficult to reduce metals that have high E⁰.
If the difference between the E⁰ values of two metals is positive, then the value of
ΔG⁰ will be negative.
Hence, the less reactive metal will come out of the solution and the more reactive metal will go into the solution.
Aⁿ⁺ + B → A + Bⁿ⁺

Question. Define refining and what are the techniques through which refining is done explain?
Answer. Refining is the process of reducing the impurities in a substance. A metal extracted by any method is usually contaminated with some impurity. The techniques used for refining impurities are:
1. Distillation: distillation is a very useful for low boiling metals. The impure metal is evaporated to obtain the pure metal as distillate.
2. Liquation: Liquation is a method with a low melting metal. In this method it is separated from higher melting impurities.
3. Electrolytic refining: In this method the impure metal is made to act as a node.A strip of the same metal in pure form is used as cathode. They are put in the suitable electrolytic bath containing soluble slat of the same metal. Copper is refined by using an electrolytic method.
4. Zone refining: in this method it is based on the principle that the impurities are more soluble in the melt than in the solid state of the metal. A mobile heater surrounding the rod of impure metal is fixed at its one end.
5. Vapour phase refining: it is the method the metal s converted into its volatile compound which is collected and decomposed to give pure metal. The two requirements are:
1. The metal should form a volatile compound with an available reagent.
2. The volatile compound should be easily decomposable so that the recovery id easy.
6. Chromatographic methods: It is based on the principle of separation or purification by chromatography which is based on differential adsorption on an adsorbent. In column chromatography, Al₂O₃ is used as adsorbent. The mixture to be separated is taken in suitable solvent and applied on the column.

Question. Explain thermodynamic principles of metallurgy? 
Answer. The extraction of metals from the lithosphere is what we call metallurgy and chemists take help of thermodynamic principles to help with this process. Thermodynamic considerations are very important in deciding the temperature and suitable reducing agent for the reduction of particular metal oxide to metallic state during extraction of metals. The Gibbs energy equation that relates to the enthalpy and entropy of the system at a certain temperature ΔG = ΔH - TΔS, where ΔG = Gibbs Free Energy Change, ΔH = Change in Enthalpy, T = Temperature, ΔS = Change in Entropy, Spontaneous Process → ΔG = negative, Non-Spontaneous Process → ΔG = positive. According to Gibbs energy free energy can be utilized to do useful work. The term ΔH represents the enthalpy change and ΔS is the change in entropy at temperature T. Relation between free energy change and equilibrium constant, ΔG = -RTlnK. The equilibrium constant K is obtained by taking the ratio of equilibrium concentrations of reactants and products. When a reaction proceeds from reactants to products, products are present in excess and equilibrium constant is positive. Alternatively, the equilibrium constant is negative for a reverse reaction. For ΔG to be negative, the change in entropy should be positive and on increasing the temperature, the value TΔS should exceed the enthalpy change for the reaction. Ellingham diagrams are used as a tool in extraction of a metal in metallurgy to find the appropriate conditions for reduction of ores of important metals. In the reaction between metal oxide and carbon, carbon is the reducing agent, itself undergoes oxidation to reduce the element.

Question. Explain the significance of the leaching in the extraction of aluminium?
Answer. Leaching is a process of extracting a substance from a solid material that is dissolved in a liquid. This process is commonly referred to as extraction, particularly in the chemical industry. Three basic steps are involved in the leaching process: contact, separation, and extraction. Leaching occurs when the air spaces in soil become filled with water and gravity begins to move water downward. The percolating water carries any soluble salts that are present in the soil and is not specific for nitrate. The significance of leaching is to concentrate pure alumina (Al₂O₃) from bauxite ore. Bauxite usually contains silica, iron oxide, and titanium oxide as impurities. In this process, hydrated Al₂O₃ gets precipitated and sodium silicate remains in the solution.

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