Principles of Metallurgy

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I. CONCEPTUAL UNDERSTANDING

1. List three metals that are found in nature as oxide ores? (AS 1) (2 Marks)

A: * Aluminium, Manganese, Ferrous (Iron) and Zinc are some metals which are found in nature as oxide ores.

2. List three metals that are found in nature in uncombined form. (2 Marks)

A: * The following metals are found in nature in uncombined form or free state.

* a) Gold (Au) b) Silver (Ag) c) Platinum (Pt) d) Copper (Cu)

3. Write a note on dressing of ore in metallurgy? (2 Marks)

A: Dressing of the ore or concentration of the ore:

* Ores that are mined from the earth are usually contaminated with large amount of impurities such as soil, and sand etc.

* Concentration or dressing means, simply getting rid of as much of the unwanted rocky material as possible from the ore.

* The impurities like clay are called gangue.

* The physical methods adopted in dressing the ore depends upon the difference between the physical properties of ore and gangue.

* The following physical methods are adopted for dressing the ore.

a) Hand picking b) Washing c) Froth flotation d) Magnetic separation.

4. What is an ore? On what basis a mineral is chosen as an ore? (2 Marks)

A: Ore: The minerals from which the metals are extracted without economic loss are called ores.

* A mineral is chosen as an ore based on the following conditions.

a) The percentage of the metal in that mineral.

b) Economic feasibility of extracting it from the mineral.

c) Convenience of extracting it from the metal.

5. Write the names of any two ores of Iron? (1 Mark)

A: The names of ores of Iron are

1) Heamatite (Fe₂O₃) 2) Magnetite (Fe₃O₄)

6. How do metals occurs in nature? Give examples to any two types of minerals. (4 Marks)

A: * Some metals are available in nature in free state as they are least reactive.

e.g.: Gold (Au), Silver (Ag), Copper (Cu)

* Most of the metals that are found in nature are in combined state due to their more reactivity nature.

* The following are some types of ores.

7. Write short notes on froth flotation process? (4 Marks)

* This method is mainly useful for sulphide ores which have no wetting property where as the impurities get wetted.

* The ore with impurities is finally powdered and kept in water taken in a flotation cell.

* Air under pressure is blown to produce froth in water.

* Froth so produced, takes the ore particulars to the surface where as impurities settle at the bottom.

* Froth is separated and washed to get ore particles.

8. When do you use magnetic separation method for concentration of an ore? Explain with an example. (4 Marks)

* If the ore or impurity, one of them is magnetic substance and the other non-magnetic substance they are separated using electromagnets.

* The ores like Iron Pyrites (FeS), and magnetic (Fe₃O₄) are concentrated with this method.

* The crushed ore is allowed to pass through electromagnetic belts.

* The mineral particles are retained and gangue particles are thrown away.

9. Write short notes on each of the following:

a) Roasting b) Calcination c) Smelting (4 Marks)

A: a) Roasting:

* Roasting is a pyrochemical process in which the ore is heated in the presence of oxygen or air below its melting point.

* The products (like metal oxides from sulphide ore) obtained in the process also are in the solid state.

* Generally reverberatory furnace is used for roasting.

2 ZnS (s) + 3 O₂ (g) → 2 ZnO (s) + 2 SO₂ (g)

Zinc Blend

b) Calcination:

* Calcination is a pyrochemical process in which the ore is heated in the absence of air.

* The ore gets generally decomposed in the process.

e.g.: a) MgCO₃ (s) → MgO (s) + CO₂ (g)

b) CaCO₃ (s) → CaO (s) + CO₂ (g)

c) Smelting:

* Smelting is a pyrochemical process, in which the ore is mixed with flux and fuel and strongly heated.

* The heat is so strong that the ore is reduced to even metal as in the case of iron (Fe), and the metal obtained is in molten state.

* During smelting the impurities (gangue) in the ore react with flux to form slag which is removed.

* For Haematite ore (Fe₂O₃), Coke is used as fuel and lime stone (CaCO₃) is used as flux.

* The smelting is carried out in a specially built furnace known as blast furnace.

* The reactions inside the furnace are:

2 C (s) + O₂(g) → 2 CO (g)

fuel

Fe₂O₃ (s) + 3 CO (g) → 2 Fe (l) + 3 CO₂ (g)

Haematite

* CaCO₃ (s) → CaO (s) + CO₂ (g)

Lime Stone (flux) lime

CaO (s) + SiO₂ (s) → CaSiO₃ (l)

Lime Silica (gangue) Calcium Silicate (Slag)

10. What is the difference between roasting and calcination. Give one example for each. (4 Marks)
A:

Roasting	Calcination
The ore is heated in the presence of air.	The ore is heated in the absence of air.
This is used for sulphide ores. e.g.: 2 ZnS + 3 O₂ → 2 ZnO + 2 SO₂	This is used for carbonate ores. e.g.: MgCO₃ → MgO + CO₂

11. Define the terms a) Gangue b) Slag (2 Marks)
A: a) Gangue: Ores are associated with earthy or rocky materials as impurities. These impurities are called gangue.
b) Slag: The fusible mass formed by the reaction of flux and gangue is called Slag.

II: ASKING QUESTIONS AND MAKING HYPOTHESIS

12. Magnesium is an active metal if it occurs as a chloride in nature, which method of reduction is suitable for its extraction? (2 Marks)
A: * Magnesium is an active element. It occurs in chloride form as MgCl₂.
* Electrolytic reduction is suitable for extraction of magnesium from its chloride ore.

13. Mention two methods which produce very pure metals. (1 Mark)
A: The two methods which produce very pure metals are
a) Electrolysis b) Smelting
14. Which method do you suggest for extraction of high reactivity metals? Why? (2 Marks)
A: * Electrolysis is the method suggest for extraction of high reactivity metals.
* The reason for this suggestion is
a) Simple chemical reduction methods like heating to reduce the ore of these metals are not feasible.
b) The temperature required for the reduction is too high and more expensive.
c) So electrolysis method is better to extract high reactivity metals.

III. EXPERIMENTS AND FIELD INVESTIGATION

15. Suggest an experiment to prove that the presence of air and water are essential for corrosion. Explain the procedure. (4 Marks)
A: a) Corrosion: Corrosion is the deterioration of a metal, as a result of chemical reaction between it and the surroundings.
b) Experiment:
Aim: To prove that the presence of air and water are essential for corrosion.
Materials required: * 3 test tubes * 3 iron nails * oil * water
* anhydrous calcium chloride * rubber corks
Procedure:

* Take three test tubes and place clean iron nails in each of them.
* Label these test tubes A, B and C. Pour some water in test tube A and cork it.
* Pour boiled distilled water in test tube B, add about 1 ml of oil and cork it. The oil will float on water and prevent the air from dissolving in the water.
* Put some Anhydrous Calcium Chloride in test tube C and cork it. Anhydrous Calcium Chloride will absorb the moisture, if any, from the air. Leave these test tubes for a few days and then observe.
* We will observe that iron nails rust in test tube A, but they do not rust in test tubes B and C.
* In the test tube A, the nails are exposed to both air and water. In the test tube B, the nails are exposed to only water, and the nails in test tube C are exposed to dry air.
* From this activity we conclude that both air and water are necessary for corrosion (rusting) of iron.

IV. INFORMATION SKILLS AND PROJECTS

16. Collect information about extraction of metals of low reactivity Silver, Platinum, Gold and prepare a report. (4 Marks)
A: * Metals are low reactivity Silver, Platinum, Mercury and gold are often found in free state.

* The oxides of these metals can be reduced to metals by heat alone and some times by displacement from their aqueous solutions.
* We can consider an example. Cinnabar (HgS) when heated in air, first converts into HgO, and on further heating it reduces to Mercury (Hg).

V. COMMUNICATION THROUGH DRAWING AND MODEL MAKING

17. Draw the diagrams showing
a) Froth flotation b) Magnetic Separation (4 Marks)
A: a) Froth flotation

b) Magnetic Separation

18. Draw a neat diagram of Reverberatory furnace and label it neatly. (4 Marks)
A:

VI. APPRECIATION AND AESTHETIC SENSE, VALUES

19. What is activity series? How it helps in extraction of metals? (4 Marks)
A: a) Activity Series: Arrangement of the metals in the decreasing order of their reactivity is called activity series.
b) Use of activity series in extraction of metals:
* For high reactivity metals namely K, Na, Ca, Mg, Al simple chemical reduction methods like heating with C, CO to reduce the ores of these metals are not feasible.
* These metals can be extracted by electrolysis.
* Zn, Fe, Pb, Cu are metals of moderate reactivity. These are generally present as Sulphides or Carbonates in nature.
* Sulphide ores can be converted into oxides by heating them strongly in excess of air. The metal oxides are then reduced.
* Ag, Au are low reactivity metals. These are often found in free state. Their reactivity with other atoms is very low.
* The oxides of these metals can be reduced to metals by heat alone and sometimes by displacement from their aqueous solutions.

VII. APPLICATION TO DAILY LIFE AND CONCERN TO BIODIVERSITY

20. What is the thermite process? Mention its applications in daily life. (4 Marks)
A: * When highly reactive metals such as Sodium, Calcium, Aluminium etc., are used as reducing agents they displace metals of lower reactivity from the compound.
* These reactions are exothermic reactions. The amount of heat so evolved is so large that metals produced are in molten state.

* The reaction of iron oxide Fe₂O₃with Aluminium is used to join railings of railway tracks or cracked machine parts.
* This reaction is known as thermite reaction.
e.g.: 2 Al + Fe₂O₃ → Al₂O₃ + 2 Fe + Heat
Applications in daily life:
* To join railings of railway track
* To join cracked machine parts.

21. Where do we use hand picking and washing methods in our daily life? Give examples. How do you correlate these examples with enrichment of ore? (4 Marks)
A: * We use hand picking in separating stones from rice and dal.
* We use washing methods to separate dust from rice, dal, vegetables, fruits etc.
Hand Picking:
* The colour and size of the impurities is different from rice and dal. So we can easily separate them by hand picking.
* In the same way if the ore particles and the impurities are in different sizes, colour etc, we use hand picking method to separate the ore from the impurities.
Washing:
* We separate less density particles like dust from more density particles like rice, vegetables by washing.
* In a similar way the ore particles are crushed and kept on a sloppy surface. These are washed with controlled flow of water.
* Less densitive impurities are carried away by flow of water, leaving more densitive particles of the ore behind.

THINK AND DISCUSS

1. Do you agree with the statement "All ores are minerals but all minerals need not be ores" Why?
A: The statement is agreeable. Minerals are the elements or compounds of the metals which occur in nature in the earth's crust.
* The minerals from which the metals are extracted without economical loss are called ores.
* Aluminium, for example, is the most common metal in the earth's crust, occurring in most of minerals.
* However it is not economically feasible to extract it from most of these minerals.
* Instead the usual ore from which it is profitable to extract it is Bauxite - which contains from 50 - 70% of Aluminium Oxide.

QUESTIONS AND ANSWERS GIVEN IN THE LESSON
1. How the metals are present in nature? (2 Marks)
A: * Some metals like gold (Au), Silver (Ag) and Copper (Cu) are available in nature in free state (native) as they are least reactive.
* Other metals mostly are found in nature in the combined form due to their more reactivity.
* The elements or compounds of the metals which occur in nature in the earth's crust are called minerals.

2. Can you arrange the metals in Table in the order of their reactivity. (2 Marks)

A: The order of reactivity of the metals given in the table is as follows:
Ag < Cu < Pb < Mn < Fe < Zn < Al < Mg < Ca < Na

3. Can you think how do we get the metals in the activity series from their ores? (1 Mark)
A: * We get the metals in the activity series from their ores by employing various extracting methods.

4. Does the reactivity of a metal and form of its ore (Oxides, Sulphides, Chlorides, Carbonates, Sulphates) has any relation with process of extraction? (2 Marks)
A: * There is relation between the reactivity of a metal and form of its ore.
* Metals of high reactivity like K, Na, Ca, Mg, Al form compounds with other elements and exists as such in their ores.
* Metals of moderate reactivity Zn, Fe, Pb, Cu exist as Oxides, Sulphides and Carbonates and form as ores.
* Metals of low reactivity Ag, Au are available even in free state.

5. How are metals extracted from mineral ores? (2 Marks)
A: The extraction of a metal from its ore involves mainly three stages. They are
      a) Concentration or Dressing
      b) Extraction of crude metal
      c) Refining or purification of metal

6. Do you know why corrosion occurs? (1 Marks)
A: Corrosion of a metal occurs due to its reaction with water and air.

7. What are the conditions under which iron articles rust? (1 Mark)
A: Iron articles rust due to their reaction with both air and water.

8. What is the role of furnace in metallurgy? (1 Mark)
A: Furnaces are used to carry out Pyrochemical process in metallurgy.

9. How do furnaces bear large amounts of heat? (1 Mark)
A: Due to metallic lining inside the furnaces they can bear large amounts of heat.

10. Do all furnaces have the same structure? (1 Mark)
A: No, different furnaces have different structures.

ACTIVITIES

Activity: 1
1. Identify the metals present in each ore. (4 marks)
A:

Ore	Formula	Metal	Ore	Formula	Metal
Bauxite	(Al₂O₃. 2 H₂O)	Al	Zincite	(ZnO)	Zn
Copper Iron Pyrites	(CuFeS₂)	Cu	Rock salt	(NaCl)	Na
Zinc Blende	(ZnS)	Zn	Cinnabar	(HgS)	Hg
Magnesite	(MgCO₃)	Mg	Magnetite	(Fe₃O₄)	Fe
Epsom salt	(MgSO₄.7 H₂O)	Mg	Galena	(PbS)	Pb
Horn Silver	(AgCl)	Ag	Gypsum	(CaSO₄^. 2 H₂O)	Ca
Pyrolusite	(MnO₂)	Mn	Lime Stone	(CaCO₃)	Ca
Heamatite	(Fe₂O₃)	Fe	Carnallite	(KCl . MgCl₂ . 6 H₂O)	Mg

2. Classify the ores as oxides, sulphides, chlorides, carbonates and sulphates. (4 Marks)
A:

Oxides	Sulphides	Chlorides	Carbonates	Sulphates
Bauxite	Copper Iron Pyrites	Horn Silvar	Magnesite	Epsom salt
Pyrolusite	Zinc blende	Rock Salt	Lime stone	Gypsum
Haematite	Cinnabar	Carnallite
Zincite	Galena
Magnatite

3. What metals can we get from the ores mentioned in the table of question number 1? (2 Marks)
A: The following metals can be got from the ores.

1) Aluminium (A)	2) Copper (Cu)
3) Magnesium (Mg)	4) Silver (Ag)
5) Manganese (Mn)	6) Iron (Fe)
7) Zinc (Zn)	8) Sodium (Na)
9) Mercury (Hg)	10) Lead (Pb)
11) Calcium (Ca)

4. What do you notice from the table in question 2? (1 Mark)

A: It is evident from the table that for many metals the ores are oxides and sulphides.

Activity: 2
5. Write an experimental process of corrosion. (4 Marks)
A: Aim: To investigate the conditions under which iron rusts.
Materials required: * 3 test tubes * 3 iron nails
* Anhydrous Calcium chloride * Boiled distilled water * Oil.
Procedure:

Observations:
* From the above activity we observe that iron nails in test tube A rust, but the iron nails in test tubes B and C do not rust.
* In the test tube A, the iron nails are exposed to both air and water.
* In the test tube B, the iron nails are exposed to water only.
* In the test tube C, the nails are exposed to dry air only.
Conclusion:
* Thus we conclude that for the process of corrosion both water and air are necessary.
(Or)
* Iron rusts when it is exposed to both water and air.

Additional Questions and Answers
1. Conceptual Understanding
1. Mention some articles that are made up of metals. (2 Marks)
A:

* Ornaments made of gold	* Silver plates, glasses.
* Copper electrodes, Copper wires, Copper vessels	* Aluminium utensils, buckets
* Zinc sheets	* Nickel parts of machinery
* Iron girders	* Tin boxes... etc

2. Do metals exist in nature in the form same as that we use in our daily life? (2 Marks)
A: * Low reactive metals like Ag, Au are available in free state.
* Many metals are found in their elements or compound from in the earth crust as minerals.

3. What is Metallurgy? (1 Mark)
A: Metallurgy is the process of extraction of metals from their ores.

4. What is the difference between mineral and ore? (2 Marks)
A: * The elements or compounds of the metals which occur in nature in the earth's crust are called minerals.
* At some places, minerals contain a very high percentage of a particular metal and the metal can be profitably extracted from it.
* The minerals from which the metals are extracted without economical loss are called ores.

5. How many water molecules are present in the following ores. Write their formula. (4 Marks)
    a) Bauxite     b) Epsom salt    c) Gypsum    d) Carnallite
A: a) Two molecules of water are present in the ore.
      Bauxite: Formula: Al₂O₃ . 2 H₂O
b) 7 molecules of water are present in the ore
      Epsom Salt: Formula: MgSO₄ . 7 H₂O
c) Two molecules of water are present in the ore
     Gypsum: Formula: CaSO₄ . 2 H₂O
d) 6 molecules of water are present in the ore
     Carnallite: Formula: KCl . MgCl₂ . 6 H₂O

6. Name four sulphide ores and give their formula? (4 Marks)
A: Following are the four Sulphide ores and their formula.

Ore	Formula	Metal
a) Copper Iron Pyrites	CuFeS₂	Cu
b) Zinc blende	ZnS	Zn
c) Cinnabar	HgS	Hg
d) Galena	PbS	Pb

7. Mention two carbonate ores giving their formula. (2 Marks)
A:

Carbonate Ore	Formula	Metal
Magnesite	MgCO₃	Mg
Lime Stone	CaCO₃	Ca

8. Write the formula and the name of the metal for which it is a ore for the following.

a) Rock Salt b) Heamatite c) Horn Silver d) Zincite (4 Marks)
A:

Ore	Formula	Metal
Rock Salt	NaCl	Na
Haematite	Fe₂O₃	Fe
Horn Silver	AgCl	Ag
Zincite	ZnO	Zn

9. Write the names of the metals put under high reactivity, moderate reactivity and low reactivity. (4 Marks)
A: * Metals of high reactivity: K, Na, Ca, Mg, Al
* Metals of Moderate reactivity: Zn, Fe, Pb, Cu
* Metals of low reactivity: Ag, Cu.

10. In how many methods the reduction of a metal can be done? (4 marks)
A: Reduction of a metal from its oxide can be done by any of the following methods choosing the suitable one.
1) Chemical reduction

2) Auto reduction
3) Displacement method
4) Electrolytic reduction

11. What are the available methods for refining of a metal? (4 Marks)
A: Four methods are available for refining of a metal. They are
1) Distillation 2) Poling 3) Liquation 4) Electrolytic refining

12. Write the process of hand picking during the concentration of a ore? (2 Marks)
A: Hand picking
* If the ore particles and the impurities are different in one of the properties like colour, size etc.
* Using that property the ore particles are hand picked separating them from other impurities.

13. How is the process of washing carried on in dressing the ore? (2 Marks)
A: Washing
* Ore particles are crushed and kept on a sloppy surface.
* They are washed with controlled flow of water.
* Less densive impurities are carried away by water flow, leaving the more densive or particles behind.

14. Write a note on Froth flotation process. (2 Marks)
A: Froth flotation
* This method is mainly useful for sulphide ores which have no wetting property whereas the impurities get wetted.
* The ore with impurities is finely powdered and kept in water taken in a flotation cell.
* Air under pressure is blown to produce froth in water.
* Froth so produced, takes the ore particles to the surface whereas impurities settle at the bottom.
* Froth is separated and washed to get ore particles.

15. How is magnetic separation useful in the concentration of the ore? (1 Mark)
A: Magnetic separation
* If the ore or impurity, one of them is magnetic substance and the other non-magnetic substance they are separated using electromagnets.

16. What are the products formed when metals K, and Na react with Oxygen? (2 Marks)
A: * When metals K and Na react with Oxygen which is in limited supply K₂O and Na₂O compounds are formed.
* When these metals react with excess Oxygen in excess then form per oxides.

17. How do the metals K and Na react with cold water? (1 Mark)
A: * Metals K, Na, Ca and Mg displace H₂ from cold water with decreasing reactivity.
* It means the reaction of K with cold water is violent and the reaction violence gradually decreases and becomes very slow when Mg reacts with cold water.

18. Explain the reaction of K, Na, Ca, Mg, Al, Zn and Fe with steam and dilute strong acids. (2 Marks)
A: * From K to Fe, they displace H₂ is steam without any change in their reactivity. But the reaction of K is violent but when it comes to Fe the reaction becomes very slow.
* Metals K, Na, Ca, Mg, Al, Zn, Fe and Pb displace H₂ from dilute strong acids with decreasing reactivity.
* The reaction is explosive with K, very vigorous with Mg, steady with Fe and very slowly with Pb.

19. What happens when metals K, Na, Ca, Mg, Al, Zn, Fe, Pb, Cu, Hg, Ag, Pt and Au react with chlorine on heating? (2 Marks)
A: * All metals mentioned in the question react with chlorine on heating to form their respective chlorides but with decreasing reactivity from top to bottom.
* This is understood from the heat evolved when the metal reacts with one mole of chlorine gas to form chloride.
* KCl, NaCl, CaCl₂, MgCl₂, Al₂Cl₃, ZnCl₂, FeCl₃, PbCl₂, CuCl₂, HgCl₂, AgCl, PtCl₃ and AuCl₃ are formed.

20. Why do we call Oxygen - Sulphur group as Chalcogen family?
A: * We know that most of the ores of many metals are oxides and sulphides.
* This is the reason why we call Oxygen - Sulphur group as Chalcogen family. Chalco means ore, genus means produce.

21. How do you understand the order of reactivity of metals? What is activity series? (2 Marks)
A: * Extraction of the metal from its ores depends on the reactivity of the metal.
* To understand the order of reactivity of metals that are very familiar, we study their chemical reactions with cold water, steam, dilute strong acids and Cl₂ and based on their vigorous activity order in these reactions we frame out activity series.
* Arrangement of the metals in decreasing order of their reactivity is known as activity series.

22. How is the extraction of metals at the top of the activity series done? (4 Marks)
A: * (K, Na, Ca, Mg and Al). Simple chemical reduction methods like heating with C, CO etc to reduce the ores of these metals are not feasible.
* The temperature required for the reduction is too high and more expensive.
* To make the process economical, electrolysis methods are to be adopted.
* Again the electrolysis of their aqueous solutions also is not feasible because water in the solution would be discharged at the cathode in preference to the metal ions.
* The only method viable is to extract these metals by electrolysis of their fused compounds.
* For example to extract Na from NaCl, fused NaCl is electrolysed with steel cathodes (^_) and graphite anode (+).
* The metal (Na) will be deposited at cathode and chloride liberated at the anode.
* At cathode 2 Na⁺ + 2 e^- → 2 Na
At anode 2 Cl^- → Cl₂ + 2 e^-
* For the above electrolysis a large quantity of electricity is required to keep the ore in molten state.
* Suitable impurities are added to the ore to decrease its melting point.

23. Describe the process of extraction of metals in the middle of the activity series? (2 Marks)
A: (Zinc, Iron, Tin, Lead and Copper): The ores of these metals are generally present as sulphides or carbonates in nature.
* Therefore prior to reduction of ores of these metals, they must be converted into metal oxides.
* Sulphide ores are converted into oxides by heating them strongly in excess of air. This process is known as roasting.
* Generally the sulphide ores are roasted to convert them into oxides before reducing them to metal.
e.g.: 2 PbS + 3 O₂ → 2 PbO + 2 SO₂
* The metal oxides are then reduced to the corresponding metal by using suitable reducing agent such as carbon.

24. How are the reduction of metal oxides processed? (2 Marks)
A: * Reduction of metal oxides with carbon: The oxides are reduced by coke in a closed furnace which gives the metal and carbon monoxide (CO).

* Reduction of oxide ores with CO.

25. Explain auto (self) reduction of sulphide ores? (2 Marks)
A: * Auto (self) reduction of sulphide ores: In the extraction of Cu from its sulphide ore, the ore is subjected partial roasting in air to give its oxide.
2 Cu₂S + 3 O₂ → 2 Cu₂O + 2 SO₂
* When the supply of air is stopped and the temperature is raised. The rest of the sulphide reacts with oxide and forms the metal and SO₂.
2 Cu₂O + Cu₂S → 6 Cu + 2 SO₂

26. How is reduction of ores done by more reactive metals? (4 Marks)
A: Reduction of ores (compounds) by more reactive metals.
* Thermite process involves the reaction of metal oxides with aluminium.
* When highly reactive metals such as Sodium, Calcium, Aluminium etc., are used as reducing agents, they displace metals of lower reactivity from the compound.
* These displacement reactions are highly exothermic. The amount of heat evolved is so large that the metals produced are in molten state.

* The reaction of Iron (III) oxide (Fe₂O₃), with Aluminium is used to join railings of railway tracks or cracked machine parts. This reaction is known as the thermite reaction.
   b) 2 Al + Fe₂O₃ → Al₂O₃ + 2 Fe + Heat
        2 Al + Cr₂O₃→ Al₂O₃ + 2 Cr + Heat

27. Describe the method of extraction of metals at the bottom of the activity series.       (2 Marks)
A: Extraction of metals at the bottom of the activity series (Ag, Hg etc)
* Metals at the bottom of the activity series are often found in free state.
* Their reactivity with other atoms is very low.
* The oxides of these metals can be reduced to metals by heat alone and sometimes by displacement from their aqueous solutions.
* When cinnabar (HgS) which is an ore of mercury, heated in air, it is first converted into (HgO) then reduced to mercury on further heating.
e.g.: 2 HgS + 3 O₂ → 2 HgO + 2 SO₂→ 2 HgO → 2 Hg + O₂
Heat                                Heat              Heat
Displacement from aqueous solutions:
e.g.: Ag₂S + 4 CN^- → 2[Ag(CN)₂]^- + S^2-
        2[Ag(CN)₂]^- (aq) + Zn (s) → [Zn(CN)₄]^2- (aq) + 2 Ag(s)
* Here Ag₂S is dissolved in say KCN solution to get dicyanoargentate (I) ions. From these ions Ag is precipitated by treating with Zn dust powder.

28. What is refining of the metal? Explain. Mention some methods of refining? (2 Marks)
A: * The metal obtained by the reduction of the ore is usually contaminated with impurities like unchanged ore, other metals present in the ore and non metals from the anions in the ore.
* For example, the (blister) Copper obtained from its sulphide ore, a compound of Copper iron pyrites (CuFeS₂), contains some Copper sulphide, iron and Sulphur.
* It is purified by suitable methods including electrolysis.
* The process of obtaining the pure metal from the impure metal is called refining of the metal.
* Refining of the metal involves several types of processes. Some refining methods are given below:
(a) Distillation (b) Poling (c) Liquation (d) Electrolysis etc.

29. Write a note on a) Distillation b) Poling and c) Liquation. (each 1 Mark)
A: a) Distillation
* This method is very useful for purification of low boiling metals like Zinc and Mercury containing high boiling metals as impurities.
* The extracted metal in the molten state is distilled to obtain the pure metal as distillate.

b) Poling:
* The molten metal is stirred with logs (poles) of green wood. The impurities are removed either as gases or they get oxidized and form scum (slag) over the surface of the molten metal.
* Blister copper is purified by this method.
* The reducing gases, evolved from the wood, prevent the oxidation of Copper.
c) Liquation:
* In this method a low melting metal like tin can be made to flow on a sloppy surface to separate it from high melting impurities.

30. Give some examples of corrosion. (1 Mark)
A: The rusting of iron (iron oxide), tarnishing of Silver (Silver sulphide), development of green coating on Copper (Copper carbonate) and Bronze are some of the examples of corrosion.

31. What is corrosion? Explain the phenomenon of corrosion? (4 Marks)
A: Corrosion: Corrosion is the deterioration of a metal as a result of chemical reaction between it and the surrounding environment, phenomenon of corrosion.
* In metallic corrosion, a metal is oxidised by loss of electrons generally to Oxygen and result in the formation of oxides.
* Corrosion of iron (commonly known as rusting) occurs in presence of water and air.
* The chemistry of corrosion is quite complex but it may be considered essentially as an electrochemical phenomenon.
* During corrosion at a particular spot on the surface of an object made of iron, oxidation takes place and that spot behaves as anode. We can write the reaction as.
Anode: 2 Fe(s) → 2 Fe₂⁺ + 4 e^-
* Electrons released at this anodic spot move through the metal and go to another spot on the metal and reduce Oxygen at that spot in presence of H⁺ (which is believed to be available from H₂CO₃ formed due to dissolution of carbon dioxide from air into water in moist air condition of atmosphere.
* Hydrogen ion in water may also be available due to dissolution of other acidic oxides from the atmosphere.
* This spot behaves as cathode with the reaction is.
Cathode: O₂(g) + 4 H⁺(aq) + 4 e^- → 2 H₂O(l)
The overall reaction is: 2 Fe(s) + O₂(g) + 4 H⁺(aq) → 2 Fe₂⁺(aq) + 2 H₂O(l)
* The ferrous ions are further oxidised by atmospheric Oxygen to Ferric ions which come out as rust in the form of hydrated Ferric oxide (Fe₂O₃XH₂O) and with further production of Hydrogen ions.

32. What is the role of furnace in metallurgy? Describe its structure. (2 Marks)
A: Furnace: Furnace is the one which is used to carry out pyrochemical processes in metallurgy.
Structure:
* We have mainly three parts in a furnace known as Hearth, chimney and fire box.
* Hearth is the place inside the furnace where the ore is kept for heating purpose.
* Chimney is the outlet through which flue (waste) gases go out of the furnace.
* Fire box is the part of the furnace where the fuel is kept for burning.

33. Write a note on Flux: (2 Marks)
A: Flux: Flux is a substance added to the ore to remove the gangue from it by reacting with the gangue.
* If the impurity (gangue) is acidic substance like SiO₂, basic substance like CaO is used as flux and if the impurity is of basic nature like FeO acidic flux like SiO₂ is added to the gangue.
* CaO _(s) +      SiO₂ _(s) →      CaSiO₃ _(l)
Flux          Silica (gangue)            Calcium silicate (slag)
* FeO _(s) +     SiO₂ _(s) →      FeSiO₃
    Gangue           flux                       Calcium silicate (slag)

II. ASKING QUESTIONS AND MAKING HYPOTHESIS

34. How do the different furnaces differ in their structures? (2 Marks)
A: * In Blast furnace both fire box and hearth are combined in big chamber which accommodates both ore and fuel.
* Reverberatory furnace has both fire box and hearth separated, but the vapours (flame) obtained due to the burning of the fuel touch the ore in the hearth and heat it.
* In furnaces like retort furnaces there is no direct contact between the hearth or fire box and even the flames do not touch the ore.

III. EXPERIMENTATION AND FIELD INVESTIGATION

35. Describe the Process of electrolytic refining. (4 Marks)
A: 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 required metal gets deposited on the cathode in the pure form.

* The metal, constituting the impurity, goes as the anode mud. The reactions are:

Anode: M → Mn⁺+ ne^-
Cathode: Mn⁺ + ne^-→ M
(M - pure metal)
Where n = 1, 2, 3, ......
* We use this electrolytic method to refine Copper.
* For this an impure Copper is taken as anode and pure copper strips are taken as cathode.
* The electrolyte is an acidified solution of Copper sulphate.
* As a result of electrolysis copper in pure form is transferred from the anode to the cathode.
Anode: Cu → Cu²⁺ + 2e^-
Cathode: Cu²⁺ + 2 e^- → Cu
* The soluble impurities go into the solution, where as insoluble impurities from the blister Copper get deposited at the bottom of anode as anode mud which contains antimony Selenium, TELLURIUM, Silver, Gold and Platinum; recovery of these elements may meet the cost of refining.
* Zinc may also be refined this way.

IV. INFORMATION SKILLS AND PROJECTS

36. Describe the reactivity of metals with Oxygen, Cold Water, Steam, Dilute Strong Acids and Chlorine on heating in a tabular form. (4 Marks)
A:

V. COMMUNICATION THROUGH DRAWING AND MODEL MAKING.

37. Draw the flow chart showing various stages involved in extraction of metal from the ore.
A:

38. Draw a neat diagram of the blast furnace and label its parts. (4 Marks)
A:

VII. APPLICATION TO DAILY LIFE, CONCERN TO BIO DIVERSITY

39. How do you prevent corrosion? What are its advantages? (4 Marks)
A: Prevention of Corrosions:
* One of the simplest methods of preventing corrosion is to prevent the surface of the metallic object to come in contact with atmosphere.
* This can be done by covering the surface with paint or by some chemicals. (e.g.: bisphenol)
* Another simple method is to cover the surface by other metals (Sn, Zn etc) that are inert or react themselves with atmosphere to save the object.
* This is generally done by electro plating.
* An electrochemical method is to provide a sacrificial electrode of another metal (like Mg, Zn etc) which corrodes itself but saves the object.
Advantages:
* Prevention of corrosion is of prime importance.
* It not only saves money but also helps in preventing accidents such as a bridge collapse or failure of a key component due to corrosion.

Do You Know?
Alloying is a method of improving the properties of a metal. We can get desired properties by this method. For example, iron is the most widely used metal. But it is never used in its pure state. This is because pure iron is very soft and stretches easily when hot. But, if it is mixed with a small amount of carbon, it becomes hard and strong. When iron is mixed with nickel and chromium we get stainless steel which will not rust. Pure gold, known as 24 carat gold, is very soft. It is therefore, not suitable for making jewellry. It is alloyed with either silver or copper to make it hard. Generally in India 22 carat gold is used for making ornaments. It means that 22 parts of pure gold is alloyed with 2 parts of either silver or copper.

Posted Date : 06-11-2021

గమనిక : ప్రతిభ.ఈనాడు.నెట్‌లో కనిపించే వ్యాపార ప్రకటనలు వివిధ దేశాల్లోని వ్యాపారులు, సంస్థల నుంచి వస్తాయి. మరి కొన్ని ప్రకటనలు పాఠకుల అభిరుచి మేరకు కృత్రిమ మేధస్సు సాంకేతికత సాయంతో ప్రదర్శితమవుతుంటాయి. ఆ ప్రకటనల్లోని ఉత్పత్తులను లేదా సేవలను పాఠకులు స్వయంగా విచారించుకొని, జాగ్రత్తగా పరిశీలించి కొనుక్కోవాలి లేదా వినియోగించుకోవాలి. వాటి నాణ్యత లేదా లోపాలతో ఈనాడు యాజమాన్యానికి ఎలాంటి సంబంధం లేదు. ఈ విషయంలో ఉత్తర ప్రత్యుత్తరాలకు, ఈ-మెయిల్స్ కి, ఇంకా ఇతర రూపాల్లో సమాచార మార్పిడికి తావు లేదు. ఫిర్యాదులు స్వీకరించడం కుదరదు. పాఠకులు గమనించి, సహకరించాలని మనవి.