Q: Which one is malachite from the following?

Malachite : CuCO3.Cu(OH)2 (Green colour)

Q: In the extraction of copper from its sulphide ore, the metal is finally obtained by the reduction of cuprous oxide with:

Self reductionCu2S+2Cu2O→6Cu+SO2↑

Q: Why is the extraction of copper from pyrites more difficult than that from its oxide ore through reduction?

In the Ellinggam diagram (graph of ΔrGo vs T) for the formation of oxides, copper-copper oxide line is almost at the top. Hence, oxide ores of copper can be easily reduced to copper by heating with coke. The ΔGo vs T lines for CO show negative slope at high temperature. Hence, it can easily reduce copper oxide to copper. However, ΔGf for sulphide ores are higher than that for CS2 (which is an endothermic compound). Hence, the extraction of copper from pyrite ore is difficult.

Q: Out of C and CO, which is a better reducing agent at 673K?

At 673 K, the ΔGo vs T line for CO, CO2 is lower than that of C, CO line. Hence, CO can be used as better reducing agent than C at 673 K.

Question 1

Identify the correct statement from the following :

Accepted Answer

The iron obtained from blast furnace contains about 4% carbon and many impurities like S, P, Si, Mn in smaller amount. This is known as pig iron and cast into variety of shapes.

Question 2

Which one is malachite from the following?

Accepted Answer

Malachite : CuCO3​.Cu(OH)2​ (Green colour)

Question 3

Considering Ellingham diagram, which of the following metals can be used to reduce alumina?

Accepted Answer

The metal which is more reactive than 'AI' can reduce alumina i.e. 'Mg' should be the correct option.

Question 4

Match items of column I with the items of column II and assign the correct code:

Accepted Answer

a] Cyanide process is used to extract and Au in hydrometallurgy.b] Froth foundation process is used for dressing of sulfide ores.c] Electrolytic reduction is used to extract Al.d] Zone refinining process is used for obtaining ultrapure Ge.

Question 5

Roasting of sulphides gives the gas X as a byproduct. This is a colorless 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:

Accepted Answer

Roasting process carried out in reverberatory furnace. It is used for sulphide ore's to convert in metal oxide.MS+O2​⟶Δ​MO+SO2​(Colourless gas)

Question 6

In the extraction of copper from its sulphide ore, the metal is finally obtained by the reduction of cuprous oxide with:

Accepted Answer

Self reductionCu2​S+2Cu2​O→6Cu+SO2​↑

Question 7

Copper can be extracted by hydrometallurgy but not zinc. Explain.

Accepted Answer

More electropositive zinc (Eo=−0.76 V) is highly reactive and can not be easily displaced from zinc sulphate solution. Less electropositive copper (Eo=+0.34 V) is less reactive and can be displaced from copper sulfate solution by using more active metal such as zinc. Zn(s)+Cu2+(aq)→Zn2+(aq)+Cu(s)

Question 8

Why is the extraction of copper from pyrites more difficult than that from its oxide ore through reduction?

Accepted Answer

In the Ellinggam diagram (graph of Δr​Go vs T) for the formation of oxides, copper-copper oxide line is almost at the top. Hence, oxide ores of copper can be easily reduced to copper by heating with coke. The ΔGo vs T lines for CO show negative slope at high temperature. Hence, it can easily reduce copper oxide to copper. However, ΔGf​ for sulphide ores are higher than that for CS2​ (which is an endothermic compound). Hence, the extraction of copper from pyrite ore is difficult.

Question 9

Explain: (i) Zone refining (ii) Column chromatography.

Accepted Answer

(i) Zone refining It is used for refining Si,B,Ga,In etc. Impurities are more soluble in the molten state of metal than in solid state. There is a circular mobile heater at one end of a rod of impure metal. Heater and the molten zone moves from one end to another end. Pure metal crystallizes out of the melt and the impurities pass onto the adjacent molten zone. Repetition of this process several times segregates impurities at one end of a rod. The end with impurities can then be cut off.(ii) Column chromatography.It is used for the separation and purification. It is based on the difference in the tendency for adsorption of a metal and its impurities on a suitable adsorbent. Different components of a mixture are differently adsorbed on an adsorbent.

Question 10

Out of C and CO, which is a better reducing agent at 673K?

Accepted Answer

At 673 K, the ΔGo vs T line for CO, CO2​  is lower than that of C, CO line. Hence, CO can be used as better reducing agent than C at 673 K.

Question 11

Name the common elements present in the anode mud in electrolytic refining of copper. Why are they present?

Accepted Answer

In the electrolytic refining of copper, the anode mud contains antimony, selenium, tellurium, silver gold and platinum. These are impurities in blister copper. They are less reactive and unaffected by CuSO4​−H2​SO4​ solution and hence, settle down under anode as anode mud.

Question 12

Write down the reactions taking place in different zones in the blast furnace during the extraction of iron.

Accepted Answer

In blast furnace, iron oxides are reduced at different temperature ranges. In the lower part of the blast furnace, the temperature is as high as 2200 K. It is called combustion zone. At the top, the temperature is as low as 500−800 K. It is called reduction zone. In the lower temperature range, carbon is the reducing agent and in the higher temperature range, CO is the reducing agent. In the reduction zone (500−800 K), following reactions occur.3Fe2​O3​+CO→2Fe3​O4​+CO2​Fe3​O4​+4CO→3Fe+4CO2​Fe2​O3​+CO→2FeO+CO2​In the temperature range 900-1500 K, following reactions occur.C+CO2​→2COFeO+CO→Fe+CO2​Around 1270 K (middle portion), decomposition of limestone gives lime (CaO) and CO2​.  Lime is a flux and combines with silicate impurity to form slag of calcium silicate.CaCO3​→CaO+CO2​CaO+SiO2​→CaSIO3​

Question 13

Write chemical reactions taking place in the extraction of zinc from zinc blende.

Accepted Answer

During extraction of Zn from zinc blende (ZnS), following reactions occur:(i) ZnS is roasted in excess air at 1200 K to form ZnO.2ZnS+2O2​Δ​2ZnO+2SO2​(ii) ZnO is heated with crushed coke at 1673 K, where it is reduced to Zn.ZnO+C1676K​Zn+CO(iii) Electrorefining is carried out for refining of impure zinc. Anode is impure zinc and cathode is pure zinc. Electrolyte is a mixture of zinc sulphate and dilute sulphuric acid (small amount). When current is passed, zinc is deposited on cathode and is collected.At anode : Zn→Zn2+ +2e−At cathode: Zn2++2e−→Zn

Question 14

State the role of silica in the metallurgy of copper.

Accepted Answer

During roasting, copper pyrites give FeO and Cu2​O.2CuFeS2​+O2​Δ​Cu2​S+2FeS+SO2​2Cu2​S+3O2​Δ​2Cu2​O+2SO2​2FeS+3O2​→2FeO+2SO2​Roasted ore is then mixed with silica (acidic flux) and heated to remove FeO (basic) as a slag of iron silicate.FeO+SiO2​→FeSiO3​Lighter slag forms upper layer and is removed through slag hole.

Question 15

What is meant by the term chromatography?

Accepted Answer

Chromatography is the technique for separating the components, or solutes, of a mixture based on the relative amounts of each solute distributed between a moving fluid stream, called the mobile phase, and a contiguous stationary phase. The mobile phase may be either a liquid or a gas, while the stationary phase is either a solid or a liquid.

Question 16

What criterion is followed for the selection of the stationary phase in chromatography?

Accepted Answer

The stationary phase is an adsorbent and has following characteristics:(1) Its adsorption power should be high and selective.(2) To offer greater surface area for adsorption, it should be finely divided.(3) It should have high mechanical stability. This will prevent dust formation.(4) It should be chemically inert to sample and eluting solvents. (5) It should have high purity.

Question 17

Describe a method for refining nickel.

Accepted Answer

The method for refining nickel involves the following:Ni is heated with CO to form volatile nickel tetracarbonyl.Ni+4CO330−350K​Ni(CO)4​At high temperature, nickel tetracarbonyl decomposes to pure Ni.Ni(CO)4​450−470K​Ni+4COThis is Mond's process for refining Ni.

Question 18

How can you separate alumina from silica in a bauxite ore associated with silica? Give equations, if any.

Accepted Answer

Bauxite ore containing silica is heated with conc. NaOH solution at 473−523 K and 35−36 bar pressure.  Alumina forms sodium aluminate and silica forms sodium silicate. Impurities are left behind. Al2​O3​+2NaOH+3H2​O→2Na[Al(OH)4​]Carbon dioxide neutralizes the aluminate to precipitate hydrated alumina.2Na[Al(OH)4​]+2CO2​→Al2​O3​.xH2​O+2NaHCO3​Sodium silicate remains in the solution and hydrated alumina is filtered and dried. On heating, hydrated alumina gives pure alumina.Al2​O3​.xH2​O1473 K​Al2​O3​(s)+xH2​O

Question 19

Differentiate between roasting and calcination with examples.

Accepted Answer

Calcination Roasting  Ore is heated in absence of air.Fe2​O3​⋅xH2​OΔ​Fe2​O3​+xH2​OZnCO3​Δ​ZnO+CO2​CaCO3​⋅MgCO3​Δ​CaO+MgO+2CO2​ Ore is heated in regular air supply below the melting temperature for metal.2ZnS+3O2​→2ZnO+2SO2​2Cu−2S+3O2​→2Cu2​O+2SO2​ 2PbS+3O2​→2PbO+2SO2​It is used for carbonates and oxide ores.  It is used for sulphide ores.Moisture and organic impurities are removed. Volatile impurites are removed as oxides such as SO2​,P2​O5​,As2​O4​.

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Solution for Class 12, Chemistry, General Principles and Processes of Isolation of Elements

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