1.Metals such as iron, copper, zinc, aluminium etc., have immense practical applications in our daily life.

2. Minerals: Naturally occurring inorganic substances derived from the earth crust which contains metals in their free state in their free state or in the form of compounds along with Earthy and Rocky impurities are called minerals.

3. Ores: Minerals from which high-grade metals can be conveniently and economically extracted on a large scale are called ores.

4. All ores are minerals but all minerals are not ores.

5. Alloys: Homogenous and heterogeneous mixture of two or more metals or a metal and non-metal having different characteristic properties than the constituent element is called an alloy.

Alloys are stronger, have great tensile strength and are less reactive than the individual constituent metals and nonmetals. This property makes them less susceptible towards corrosion and weathering.

6. Extraction of a metal from its corresponding oxide by elimination of oxygen is known as reduction.

7. Thermite process: Extraction of metals such as iron, chromium, manganese etc., from their oxides by heating the oxides with aluminium powder at a high temperature is known as Goldschimdst’s thermite process. A mixture of 3 parts of Fe2O3 with 1 part of aluminium powder is known as metal activity series.

8. A metal occupying a higher position ( more reactive ) in the metal activity series can displace another metal occupying a relatively lower position ( less reactive ) from the aqueous solution of its salt.

9. Metals present in the middle of the activity series such as Zn, Fe, etc., can be extracted from their ores by the carbon reduction process.

10.  Metals present at the top of the metal activity series are extracted by the electrolysis of their fused salts.

11. If an iron object is left in moist air for a long time, then a reddish-brown layer of hydrated ferric oxide( Fe2O3. H2O) is formed over the object at an ordinary temperature which is commonly known as rust.

12. Rusting of iron is accelerated in the presence of Ions like Cl-, SO42- etc. Thus, rusting becomes a major problem in the case of ships and underground pipelines.

13. Some practical methods of preventing rusting of iron are – painting the surface of the iron object coating the surface of the object with varnish, galvanization or attaching a magnesium block to the iron object (sacrificial protection). Consequently, rusting of iron is prevented.

14. When an aluminium article comes in contact with moist air, a thin non conducting layer of Al2O3 is formed over it, which protects it from further corrosion.

15. If copper objects are left in moist air for a long time, a green layer( basic copper carbonate) is formed over those objects.

16. Food items or fruits containing acids should not be stored or processed in containers made up of Al, Zn or Cu as it may lead to toxicity of food.

MCQ:

1.The core of an Electromagnet is made of

Cast iron      B. Steel          C. Wrought Iron   D. Magnetite

2. The metal used in making of electrolytic cells and dry cells is

Al                 B. Sn             C. Zn                   D. Cu

3. Which of the following is the purest form of iron?

Cast iron     B. Wrought Iron C. Steel        D. Invar

4. The amount of carbon present in steel is

0.01-0.2%    B. 0.15-1.5%        C. 2-4.5%     D. 5-5.6%

5. Which of the following is not a constituent of the alloy, duralumin?

Copper        B. Magnesium     C. Manganese D. Nickel

6. An Ore containing only one metal is

7. Copper pyrites B. Iron pyrite  C. Zinc blende  D. Bauxite

8. The percentage of silver in German Silver is

2-5%            B. 5-10%              C. 10-15%       D. 0%

9. Which of the following alloys does not contain zinc as a constituent metal?

Brass          B. German Silver  C. Bell metal  D. Gem metal

10. Which of the following alloy does not contain Nickel as a constituent metal?

Stainless steel B. Manganese steel  C. German silver D. Invar

11. Which of the following mineral is not an ore?

Red haematite B. Zinc blende  C. Bauxite   D. Iron pyrites

12. The oxide ore of zinc is

Calamine         B. Zinc blende   C. zincite     D. Willemite

13. Tin-amalgam is used

To make spectacles                             B. as a reducing agent

C.  To make mirrors                                   D. to make thermometers

14. Which of the following is a mineral of iron but not its ore?

Red haematite  B. Magnetite  C. Iron Pyrites   D. Siderite

15. During extraction of aluminium, Alumina is reduced by

H2                      B. Carbon         C. H2S           D. electrolysis

16. During extraction of zinc, ZnO is reduced by

H2                     B. Carbon powder  C. H2S    D. electrolysis

17. In thermite mixture the ratio of Fe2O3 and Al powder is

1:2                   B. 2:1                   C. 1:3          D. 3:1

18. In thermite process, the substance present apart from the thermite mixture are

Fe,Cr              B.  ZnO, Mg         C. BaO2 , Mn  D. BaO2,Mg 

19. Which of the following metals react with boiling water to evolve H2 but does not do so with cold water?

Ca                   B. K                      C. Al              D.  Na

20. Which of the following metals is placed below Pb and above Hg in the metal activity series?

Sn                   B. Ag                    C. Cu             D. Au

21. Which of the following reaction is feasible?

Zn + FeSO4                                                 B. MgSO4 + Fe

 C. CuSo4 + Ag                                                  D. ZnSO4 + Pb

22. Which of the following metals can be extracted by the thermite process?

Fe                   B. Cu                     C. Zn            D. Al

23. In thermite process, the metal used as the reducing agent is

Al                    B. Ni                      C. Zn            D. Fe

24. Metals placed at the top of the metal activity series are usually extracted by

Carbon reduction method               B. Reduction by H2

 C. self-reduction                                     D. electrolytic reduction

25. Metals placed at the middle region of the metal activity series are usually extracted by

Carbon reduction method               B. reduction by H2

   C. Self-reduction                                     D. electrolytic reduction

26. Metals which can exist in free state in nature are

a. Placed at the top of the metal activity series

b. Placed at the middle of the metal activity series

c. Placed at the bottom of the metal activity series

d. Not included in the metal activity series

27. Which of the following orders correctly represents the reactivity of metals?

Pb<Fe<Mg     B. Mg>Ca>Zn  C. Ag<Zn<Pb  D. Al>Cu>Fe

28. Which of the following metal pair reacts with both acids and alkalis to produce hydrogen gas?

Cu,Zn             B. Na,Cu            C. Pb, Zn             D. Al, Zn

29. Na cannot be extracted from its oxide by the carbon reduction process because

Oxide of Na is unstable                   B. Na does not exist in its oxide form

                  C.  Oxide of Na is more stable              D. Oxide of Na is volatile

30. Metals placed at the top of the metal activity series are

Strong reducing agents                  B. Weak reducing agents

                  C.  Strong oxidising agents                 D. Weak oxidising agents

31. In the metal activity series, the only non-metal present along with the metals is

Carbon         B. Hydrogen            C. Chlorine     D. Iodine

32. The chemical formula of Rust is

FeO.xH2O     B. Fe3O4                   C. Fe2O3          D. Fe2O3 . xH2O

33. Presence of which of the following ions accelerates the process of rusting?

Na+                B. Ca2+                     C. Cl-                D. O2-

34. Which of the following is used to protect the iron parts of ships from rusting?

Copper blocks   B. Aluminium Blocks  C. Zinc blocks  D. Magnesium blocks

35. Which of the following methods does not prevent rusting?

Painting the surface                                B. Galvanisation

                  C. Using an Mg- Block                                  D. immersing in MgCl2 solution

36. During rusting, the presence of which of the following ions in water causes the reduction of dissolved O2?

Fe2+               B. Fe3+                      C. H+     D. Self reduction occur in this case

37. To prevent rusting Mg- Block is attached to iron pipes because

a. Mg is more electropositive than Fe   

b. Mg has a greater tendency to get oxidised than Fe.

Both A and B

None of these

38. Galvanized iron is actually

Zn- coated iron      B. Sn-coated iron    C.Ni-coated iron  D. Cr-coated iron

39.  Green layer formed over Copper and most of its alloys when exposed to moist air is of

Basic copper nitrate                                B. Acidic Copper nitrate 

                  C. Basic copper carbonate                           D. Cr-coated iron

40. Which of the following metals can protect itself from corrosion?

Al                            B. Fe                           C. Na                   D. Cu

41. The white layer formed over metallic aluminium in presence of moist air is of

AlCl3                       B. Al(OH)3                   C. Al2O3               D. AIN

Answer in Single Sentence

1. Arrange wrought iron, steel and cast iron in the order of increasing carbon content present in them.

Wrought iron < Steel < Cast iron

2. Which metal is present in each of bronze, brass and bell metal.

In each of bronze, brass and bell metal copper is present.

3. What are the major constituent of stainless steel?

The major constituent of stainless steel are iron( 73%), chromium(18%) and Nickel(8%).

4. Name any two alloys of aluminium.

Two alloys of aluminium are – 1) Magnelium( Mg,Al )

                                                2) Alnico ( Al, Ni, Co, Fe).

5. Name any two alloys of iron.

Two alloys of iron are – 1) Stainless steel ( Fe, Cr, Ni and traces of carbon )

                                        2) Invar ( Fe, Ni )

6. Name any two alloys of zinc.

Two alloys of zinc are – 1) Brass ( Cu, Zn ) and 

                                        2) German Silver ( Cu, Zn, Ni ) 

7. Name some important ore of iron.

Some important ores of iron are red haematite ( Fe₂O₃), magnetite( Fe₃O₄), siderite ( FeCO₃) etc.

8. Name some important ore of copper with their formulas.

Some important ores of copper are copper pyrites [ Cu₂S . Fe₂s₃ ] or [ CuFeS₂], copper glance ( Cu₂S ), malachite [ CuCO₃ . Cu(OH)₂ ], cuprite ( Cu₂O ) etc.

9. Name the major ores of Zinc with their respective formulas.

The major ores of zinc are zinc blende ( ZnS ), Calamine ( ZnCO₃), Zincite ( ZnO ) etc.

10. Name the major ore of aluminium with their respective formulas.

The major ores of aluminium are bauxite ( Al₂O₃ . 2H₂O ) , gibbsite ( Al₂O₃ . 3 H₂O ), Cryolite ( AlF₃. 3 NaF ) etc.

11. Name a mineral of aluminium which is not considered as its ore.

China-clay ( Al₂O₃ . 2SiO₂ . 2 H₂O ) is a mineral of aluminium but is not considered as its ore.

12. Name a metal which is found in nature in its free state.

Gold(Au) is found in nature in its free state.

13. Why is invar used in making metre scale?

Invar is used in making a metre scale because its coefficient of linear expansion is very small.

14. What are Noble metals? Give examples.

The metals which are chemically not so reactive are known as Noble metals. Example: Gold, platinum.

15. Give an example of a reduction process where an anion accepts an electron.

MnO₄ + e MnO₄^2- ; In this reaction an anion accepts an electron and gets reduced.

16. Cu²⁺ + Zn Cu + Zn²⁺ – Identify the oxidant and reductant in the given reaction.

In the given reaction, Zn acts as the reductant while Cu²⁺ acts as the oxidant.

17. Name some metals other than iron that can be extracted by thermite process.

Some metals other than iron that can be extracted from their oxides by thermite process are chromium ( Cr ), molybdenum ( Mo ), Titanium( Ti ), manganese( Mn ) etc.

18. Why is aluminium used in the thermite process?

At high temperatures, aluminium exhibits strong reducing power i.e., it has strong affinity towards oxygen. For this reason, Aluminium is used in thermite process.

19. Name the element below which copper is placed in the metal activity series.

The element below which copper is placed in the metal activity series is hydrogen.

20. Arrange Pb, Ca, Cu, Zn, Mg in increasing order of their reactivity.

Cu < Pb < Zn < Mg < Ca.

21. Which metals are extracted by the carbon reduction method?

Metals which are placed in the middle region of the metal activity series are extracted by carbon reduction method.

22. Arrange Na, Al, Fe, Pb in increasing order of their reducing power.

The increasing order of reducing power of the given element is – 

Pb < Fe < Al < Na.

23. Between aluminium and Tin which one occupies a higher position in the metal activity series?

Aluminium occupies a higher position than tin in the metal activity series.

24. Name the metal which reacts only with acids to produce hydrogen(H₂).

Tin ( Sn ) reacts only with acids to produce hydrogen ( H₂ ).

25. Give the equation of the reaction in which Mⁿ⁺ ion is converted into metal M at the cathode during electrolysis of a fused salt-containing Mⁿ⁺ ion.

The equation is : Mⁿ⁺ + ne = M

26. What happens during the electrolytic reduction of fused NaCl?

During the electrolytic reduction of fused NaCl, Na is deposited at the cathode and Cl₂ gas is liberated at the anode.

27. Apart from aerial oxygen which other component of the atmosphere is responsible for rusting of iron?

Apart from aerial oxygen, water vapour is responsible for rusting of iron.

28. Which type of impurity facilitates the rusting of iron?

The presence of less electropositive metals in iron as impurities facilitates rusting.

29. Name an electrochemical process.

Rusting of iron is an electrochemical process.

30. Write the reactions that occur at the anode and cathode during rusting of iron.

Anode reaction: 2 Fe 2 Fe²⁺ + 4e

Cathode reaction: O₂ + 4H⁺ + 4e 2H₂O

31. Name a metal apart from zinc that can be used as a coating over iron to protect it from rusting.

Apart from zinc tin can be used as a coating over iron to protect it from rusting.

32. The presence of chloride Ion facilitate rusting of iron. Mention one practical disadvantage of it.

Underwater pipelines made of iron are easily corroded by rusting due to the presence of Cl^– ions in seawater.

33. How can you protect iron from rusting?

If steam is passed over red hot iron, a thin layer of ferrosoferric oxide ( Fe₃O₄) is formed over iron which protects it from rusting.

34. Write the composition of the green coloured layer formed on Copper and most copper alloy when exposed to moist air from a long time.

The green layer formed on the copper alloys on prolonged exposure to moist air is actually basic copper carbonate [ CuCO₃ . Cu(OH)₂ ].

35. What are the necessary conditions required for rusting 

The process of rusting requires

1. Presence of atmospheric oxygen,
2. Presence of water vapour.

Match The Columns

Column 1	Column 2
China Clay	Ore of Cu
Magnetite	Ore of Zn
Calamine	Mineral of Al
Malachite	mineral of Fe

Column A	Column B
K	Used to Protect the iron parts of ship from rusting
Zn	Reacts with both acid and base to produce Dihydrogen
Au	Strong reducing agent
Mg	Obtained in free state in nature

Column 1	Column 2
Ca	Reacts with steam in red hot state to produce hydrogen.
Pb	Reacts with cold water to produce hydrogen.
Cu	Reacts only with acids to produce hydrogen
Zn	Does not produce hydrogen on Reactions with acid

Fill in the Blanks

1. An explosive is prepared by mixing_
2. The percentage of carbon in wrought iron is _%
3. The non-metal present in stainless steel is_ 
4. The carbonate ore of iron is_
5. The metal occupying  the last position in the metal activity series is_
6. The amalgam of _metal is used as a reducing agent in organic reactions.
7. The alloy of aluminium used in making Electromagnet is_
8. Sn and Pb react only with_ to produce hydrogen.
9. Metals can be extracted conveniently and economically from their_
10. In the reaction 2Fe³⁺ + Sn²⁺ 2Fe²⁺ + Sn⁴⁺, Fe³⁺ acts as the _ while Sn²⁺ acts as the _.
11. Cryolite is an ore of _
12. During electrolysis, metal cations move towards the cathode and get_ by accepting_
13. A metal oxide gets_ when oxygen is removed from it.
14. The oxide ore of copper is_
15. On moving down the metal activity series reducing power of the metals gradually_
16. The extraction of a metal from the corresponding metallic compound is always a_ process.
17. The middle occupying the topmost position in the metal activity series is_
18. Magnesium reacts with_ water to evolve H₂ gas.
19. _is also known as zinc white.
20. The constituents of thermite mixture are _and_.
21. Less reactive metals are found in nature in their _state.
22. In aqueous solution, a more reactive metal can _or_ a less reactive metal from its salt.
23. Mg- blocks attached to an underground pipe carrying oil act as the_
24. Metals placed at the top of the metal activity series has _ affinity towards oxygen.
25. In the metal activity series Zn is placed_ Cu.
26. Among Fe, Cu, Zn and Al, _ occupies the highest position in the metal activity series.
27. During rusting, oxygen dissolved in water gets reduced to form_.
28. The presence of substances _ prevent rusting of iron.
29. Rusting can be prevented if iron is kept in contact with _  electropositive metals.
30. A thin Non conducting layer of _ over Al prevents the metal from getting attacked by atmospheric O₂ and moisture.
31. Acidic food or fruits should not be kept in containers made of _ or _.
32. Different weather conditions causes metallic objects to lose their _.

Answer

1. aluminium
2. o.1-o.15%
3. carbon
4. siderite
5. gold
6. sodium
7. alnico
8. acids
9. ores
10. oxidant, reductant
11. aluminium
12. reduced, electron(e)
13. reduced
14. cuprite
15. decreases
16. reduction
17. potassium
18. boiling
19. ZnO
20. Fe2O3
21. free
22. precipitate, reduce
23. anode
24. high
25. above
26. Al
27. H2O
28. alkaline
29. more
30. Al2O3
31. Al, O3
32. Al, Zn
33. lustre

State whether True or False

1. All minerals are ores, but all ores are not minerals.
2. Calamine is the chief ore of zinc.
3. Cast iron is the purest form of iron.
4. Zincite is the oxide ore of zinc.
5. The percentage of silver present in the alloy German Silver is 2-5%.
6. Tin amalgam is used to make spectacles.
7. Cl^–  ion accelerates the process of rusting.
8. During the extraction of aluminium, Alumina is reduced by carbon.
9. Copper reacts only with acid to produce hydrogen ( H₂)
10. Objects made of copper turn green on prolonged exposure to air due to the formation of basic copper carbonate.
11. It is justified to coat an iron cauldron used for cooking, with zinc to protect the Cauldron from rusting.
12. Fe can be extracted by the thermite process.
13. Metals placed at the top of the metal activity series are extracted by the carbon reduction process.
14. Al reacts with both acids and alkalis to produce hydrogen gas.
15. Metals placed at the top of the metal activity series are strong oxidizing agents.
16. Ni-coated iron is known as galvanised iron.
17. The chemical formula of Rust formed on iron is FeO. xH₂O.
18. The extraction of a metal from the corresponding metallic compound is always a reduction process.
19. Rusting occurs in the presence of water only.
20. Pure metals are weathered more readily compared to impure metals.

Answer

1. false
2. true
3. false
4. true
5. false
6. false
7. true
8. false
9. false
10. true
11. false
12. true
13. false
14. true
15. true
16. false
17. false
18. true
19. false
20. false

Short Answer Type Questions

1. Classify iron on the basis of carbon content. Which among these is the purest?

On the basis of carbon content, iron is divided into three categories – cast iron ( C : 2 – 4.5%) , wrought iron ( C : 0.1 – 0.15 % ) and steel ( C : 0.15 – 1.5 % ).

Wrought iron is the purest form of iron.

2. Write some uses of cast iron.

Cast iron is used in the making of a) Wrought iron and steel

                                                      b) tubes, iron, railing, cauldron, lamp post etc.

3. Write some uses of wrought iron.

Wrought iron is used in the making of a) core of electromagnet

                                                                  b) wires, nails, rods, chains etc.

4. Write some uses of steel.

Steel finds extensive use in modern civilization . It is used in the making of 

1. Automobiles, rails, knives , scissors , surgical instruments, ships, blades, tankers etc. 
2. Cooking utensils.
3. Alloy steel is made by adding other metals with steel.

5. Why is copper used in the making of electrical wires and instruments?

Copper is a metal of low resistance and high malleability.  Thus,  a high value of electrical conductance and also it can be easily shaped into wires. Hence, it is used in the making of electrical wires and instruments.

6. Copper is a good conductor of heat – state one application of this property.

1. Copper is used in making cooking utensils because it is a good conductor of heat.
2.  Copper is used in the construction of a calorimeter which is quite helpful in measuring the amount of absorbed or released heat.
3.  Copper is used in making boilers in factories. Being a good conductor it helps in boiling of water quickly.

7. Write some important uses of zinc.

1. Zinc is used as a reagent in the laboratory for the preparation of hydrogen.
2.  It is used in electrochemical cells and batteries.
3.  It is also used in making zinc white.
4.  zinc is coated over iron to protect it from rusting.

8. Aluminium is a light non-corrosive metal. State applications of this property.

1. Being a light metal, Aluminium is used in the manufacture of body parts of machines.
2.  As it is non-corrosive and light it is used in making the body of automobiles, aeroplanes, window frames, buckets, tanks, boxes etc.

9. Some properties of aluminium are mentioned below. State the applications of these properties – 1)  Aluminium is a good conductor of electricity

                               2)  Aluminium can be easily beaten into thin sheets.

Aluminium is a good conductor of electricity. Hence, it is used for making electrical wires and electrical instruments.

Aluminium can be easily beaten into thin sheets. Due to this property, aluminium is used in making packing foils.

10. Define minerals. Give examples.

Minerals may be defined as the naturally occurring inorganic substances found in Earth’s crust or on Earth’s surface which contain metals in their native state or in the form of compounds mixed with other impurities. Example- red haematite ( Fe₂O₃ ), magnetite ( Fe₃O₄ ), iron pyrites ( FeS₂ ) are minerals containing iron.

11. Define ores. Give examples.

The minerals from which a metal can be conveniently and economically extracted are known as ores of the metal. For example – High quality iron can be conveniently and economically extracted from Red haematite ( Fe₂O₃). Hence, red haematite is the ore of iron. Similarly, malachite [ CuCO₃ . Cu(OH)₂] is an ore of copper.

12. Discuss the electronic theory of oxidation and reduction. 

The process of removal of one or more electrons from an atom or ion is known as oxidation.

Example: Na Na⁺ + e , Fe²⁺ Fe³⁺ + e

The process of acceptance of one or more electrons by an atom or ion is known as reduction.

Example: Cl + e Cl^– , Na⁺ + e Na

13. What is a thermite mixture? Write two practical applications of the thermite process.

A mixture of 3 parts of ferric oxide by mass with 1 part of powdered Aluminium is known as thermite mixture.

• Some important applications of thermite process are discussed below-

1. Thermite process is applied in repairing broken parts of rails, tramlines, ships, machines made of iron etc.
2. Metals like chromium, manganese etc., are extracted by thermite process.

14. What do you mean by metal activity series? Name the metals at the top and bottom of the series.

The series obtained by vertically arranging the metals from top to bottom in decreasing order of their electropositivity or decreasing order of chemical reactivity is called metal activity series. The metal placed at the top of the series is Potassium (k) while gold (Au) is placed at the bottom.

15. Arrange Cu, Fe, Ag and Zn in increasing order of their reactivity on the basis of the following reactions.

CuSO₄ + Fe FeSO₄ + Cu

2AgNO₃ + Cu Cu( NO₃)₂ + 2 Ag

FeSO₄ + Zn ZnSO₄ + Fe

More reactive metal replaces a less reactive metal from its salt. So, according to reaction

1. Fe is more reactive than Cu. According to reaction
2. Cu is more reactive than Ag. According to reaction 
3. Zn is more reactive than Fe.

Hence, the order of increasing reactivity:

   Ag < Cu < Fe < Zn.

16.  When an iron nail is dipped into an aqueous solution of copper sulphate a 

              reddish-brown layer is developed over the nail. Explain why.

A metal occupying a higher position relative to another metal in the metal activity series can replace the latter from the solution of its salt. In metal activity series, iron is placed above copper. Hence iron can replace copper from copper sulphate solution. When an iron nail is dipped into an aqueous copper sulphate solution, reaction takes place between them at the surface of iron nail and hence a reddish brown layer of metallic copper is formed over the iron nail.

                                         Fe + CuSO₄ FeSO₄ + Cu( red )

17.  What happens when a piece of zinc is added to an aqueous solution of copper 

             Sulphate?

In the metal activity series zinc is placed above copper. Hen zinc can replace copper from copper sulphate solution. So when a small piece of zinc is dipped in copper sulphate solution, the reaction takes place between zinc and copper sulphate and copper is precipitated. The precipitated copper deposits on the surface of zinc and hence a reddish-brown layer is formed over zinc.

                              Zn + CuSO₄ ZnSO₄ + Cu( red )

18.  What is the carbon reduction process of metal extraction?

Reduction of metal oxide by heating the mixture of metal oxide with carbon at a very high temperature in a blast furnace is called the carbon reduction process. “ Coke powder” is used as a reducing agent for this process. Besides, CO produced due to incomplete oxidation of carbon also acts as a reducing agent.

19.  Aluminium cannot be extracted by the carbon reduction process. Explain with 

               Reasons.

Aluminium occupies the top portion of the metal activity series. Hence, it is a highly reactive metal and possesses strong reducing property. Carbon reduction process is applicable for the extraction of those metals which have relatively greater tendency to combine with carbon than oxygen. However, aluminium has a greater tendency to combine with oxygen than carbon and also the oxide of aluminium( Al₂O₃) is more stable as compared to the oxides of carbon. The aluminium cannot be extracted by carbon reduction process. Al is generally extracted by electrolysis of molten alumina ( Al₂O₃).

20.  Which method is suitably used for the extraction of metals ( such as Fe, Zn etc.) 

              Occupying the middle part of the metal activity series? Explain with reasons.

The metals occupying the middle part of the metal activity series are moderately reactive and hence have relatively less tendency than carbon to combine with oxygen. Therefore, these metals can be extracted from their oxides by the carbon reduction process at high temperatures.

Example: ZnO + C(coke) Zn + CO

21. Why are the metals occupying lower positions in the metal activity series often 

             found in nature in their native state?

The metals occupying the lower position in the metal activity series( Hg, Ag, Au ) Have very little chemical reactivity. Hence, they are not easily affected by atmospheric oxygen, water vapour, CO₂, etc., and thus exist in nature in their native state.

22.  What is corrosion of metals?

When a piece of metal is kept in open air for a long time, the metal chemically reacts with atmospheric oxygen, CO₂, water vapour etc., and is converted into other substances.

As a result the metal piece erodes.This natural phenomenon is known as corrosion of metal.

23.  Why impure metals undergo quicker weathering as compared to the pure metals?

When a piece of a metal is kept in open air, the Impurities present in the metal acts as tiny electrochemical cells on the surface of the metal. Hence, it can be affected readily by atmospheric oxygen, water vapour etc. Pure metal generally does not form such cells and thus they are not withered easily.

24.  What do you mean by rusting of iron? Why are metal articles corroded due to rusting?

When iron or iron objects are kept in moist air for a few days, a reddish-brown layer of hydrated ferric oxide( Fe₂O₃ . x H₂O ) is formed over the objects. This reddish-brown layer is called rust and the process is called rusting.

The volume of Rust is generally greater than the volume of pure iron. Hence, after the formation of rust, the surface becomes flaky and comes out of the metal easily. Therefore, the objects undergo corrosion.

25. What are the factors which accelerates the process of rusting?

The process of rusting is accelerated by the following factors-

1. Presence of less electropositive metals in the iron as an impurity.
2. The presence of gases like CO₂, SO₂, SO₃, NO, NO₂ etc.
3. Presence of chloride( Cl^–) or sulphate ( SO₄^2-) ions in water.

26. Why is rusting called ‘ slow combustion ‘?

In the presence of Ideal Oxygen and water vapour, iron is oxidised to hydrated ferric oxide( Fe₂O₃ . xH₂O ) or rust. During this process, small amount of heat is also produced. Hence, it is sometimes called a slow combustion.

27. Oil pipelines through oceans are more susceptible to resting. Explain why.

Ocean water contains a large volume of dissolved Oxygen and a huge quantity of chloride ions. In presence of chloride ions, the process of rusting is accelerated. Hence, oil pipelines through oceans are easily rusted.

28. What do you mean by galvanization?

To protect iron from rusting and corrosion, sometimes a zinc coating is applied over iron object mainly by electrolytic method. This is known as galvanization. Iron coated with zinc is called galvanized iron.

29. Why is zinc used in galvanization to prevent rusting?

In the metal activity series zinc is placed above iron. Hence, zinc is more electropositive than iron and it is more easily oxidized than iron. So, when iron is coated with zinc, drink is more readily affected by Oxygen and water vapour. This protect iron from being oxidized. Thus,  rusting is prevented.

30. Zn is more electropositive than iron so it should be corroded more readily than iron. But this doesn’t happen. Instead, zinc is coated over Iron to prevent rusting. How will you explain this?

When zinc is exposed to wear it is affected by oxygen, CO₂ To and water vapour present in the air to form a layer of of basic zinc carbonate [ Zn(OH)₂ . ZnCO₃].

This layer kills zinc from atmospheric air and hence for the corrosion is prevented. This is why zinc is used to protect iron from rusting.

31. Will it be justified to coat an iron Cauldron, used for cooking, with zinc to protect the Cauldron from rusting?

The melting point of zn is 420°C while that of iron is 1525°C, i.e., zinc has a much lower melting point than Iron. At about 250°C, zinc becomes brittle and the layer may break on application of higher temperature. Hence, it is not suitable to coat an iron Cauldron,  used for cooking, with zinc to protect the Cauldron from rusting.

32. Explain why tin plated utensils are used instead of zinc plated utensils to store food.

Zinc is more effective in preventing rusting and corrosion. Yet, tin-plated containers are widely used to store food than zinc-plated containers  because zinc may react with some acids present in food to produce toxic substances which may cause food poisoning. Hence, it is safe to use tin-plated containers to store food

33. Why is aluminium called self protecting metal?

When metallic Aluminium is kept in moist air, it reacts Oxygen and water vapour to form a nonconducting thin layer of Aluminium oxide(Al₂O₃) over its surface. As a result, the metallic lustre is lost. But, the layer formed is insoluble in water and protects the metal from further oxidation. Hence, corrosion of the metal is prevented. This is why Aluminium is called a self-protecting metal.

34. Copper objects turn green when kept in air for a long time. Explain.

When exposed to moist air for a long period of time, copper is oxidized by aerial oxygen to Copper oxide( CuO ) which deposits on the surface of the object. Due to presence of H₂S In the air of industrial area, black layer of copper sulphide( CuS ) is formed on the surface of the article. This layer is further oxidized to form green coloured basic copper sulphate [ CuSO₄ . 3Cu(OH)₂]. Sometime, copper is also oxidized by O₂, CO₂ and water vapour to Green coloured basic copper carbonate [ CuCO₃ . Cu ( OH )₂ ]. Due to the formation of these compounds, the object turns green.

35. Copper vessels are sometimes cleaned with lemon or tamarind. What is the possible reason for this?

Copper vessels are oxidized by O₂, CO₂ and water vapour to form a thin layer of green coloured basic copper carbonate [ CuCO₃ . Cu(OH)₂]. Lemon or tamarind contents organic acids. This organic acid reacts with basic copper carbonate and remove the green patches. Hence, the green patch or stain gets removed from the vessels.

36. Gold ornaments are often covered with green patches on the surfaces. Why?

To increase the strength of gold for making ornaments, copper is added as an impurity. In moist air, this copper is slowly oxidized over a long period of time to form green coloured basic copper sulphate [ CuSO₄ . Cu(OH)₂ ] or basic copper carbonate [ CuCO₃. Cu( OH )₂ ]. The green patches on the gold ornaments appears due to the formation of these compounds.

37. Explain why it is harmful to eat pickles or chutneys kept in an aluminium foil.

Vinegar is generally used as an ingredient for making pickles or chutney. Vinegar is nothing but an aqueous solution of Acetic Acid ( CH₃COOH). Thus, it reacts with aluminium to form poisonous aluminium salt. Hence, it is harmful to eat pickles are Chutneys kept in Aluminium foil as it may cause food poisoning.

38. What is an alloy? Name a common alloy and state its composition.

An alloy is a homogenous or heterogeneous mixture of two or more metals or sometimes of metals and non-metals having characteristic properties different from their constituent elements.

A common and widely used alloy is brass. It is made of copper( 60 – 80 )% and Zinc( 20-40%).

39. Differentiate between Minerals and ores.

Minerals	Ores
Minerals are inorganic substances found in the earth’s crust containing one or more metals, in their native state or as their compounds, along with impurities. For example, Copper pyrites ( Cu2S . Fe2S3) is a mineral of copper.	The minerals from which a metal can be conveniently and economically extracted involving less Complex chemical methods are called ores of that metal. For example, red haematite ( Fe2O3) and iron pyrites ( Fe2S ) both are minerals of iron but only iron pyrites is the ore of iron not haematite.
All minerals are not ores	All ores are minerals

40. All ores are minerals but all minerals are not ores – justify the statement.

Minerals are the naturally occurring inorganic substances which contain one or more metals, in their native state or as their compounds, along with impurities. On the other hand, the minerals from which a metal can be conveniently and economically extracted are called ores of that metal. Obviously , all ores are minerals. But,  we cannot extract metals from any mineral by convenient and cheap methods. hence, all minerals cannot be called ores.

For example,  both bauxite and China clay are the minerals of aluminium. But, only bauxite is considered as the ore of aluminium, not China clay. 

41. How does oxidation occur?

Oxidation takes place in three different ways-

1.  oxidation takes place when an atom loses electron(s).

Example : Na⁺ Na⁺ + e ;  Al³⁺ +3e

2. Oxidation takes place when a cation loses electron(s).

Example: Cu⁺ Cu²⁺ + e ;  Fe²⁺ Fe³⁺ + e

3. Oxidation takes place when an anion loses electron(s).

Example: S^2-S + 2e    ;      2Cl^– Cl² + 2e.

42. How does reduction occur?

Reduction takes place in four different ways-

1. Reduction takes place when an atom accepts electron(s).

Example- Cl + e Cl^– ;  O + 2e O^2-

2. Reduction takes place when a cation accepts electron(s).

Example: Na⁺ + e ;  Mg²⁺ + 2e Mg

3. Reduction takes place when an anion of lower charge accepts electron(s) and is converted into an anion of higher charge.

Example: MnO^4- + e MnO₄^2- , O^– + e O^2-

4. Reduction takes place when a cation of higher charge accepts electron and is converted into another cation of lower charge.

Example- Fe³⁺ + e Fe²⁺ ;    Sn⁴⁺ + 2e Sn²⁺

43. Extraction of metals from their ores is basically a reduction process –  explain with example.

In the ore, metal remains in a positive oxidation state but, after extraction of the metal, the oxidation number becomes zero. Thus, during extraction of the metal, the metal ion accepts electrons to become a free atom. Hence, we can say that extraction of metals from its ores is a reduction process.

                Mⁿ⁺ (metal ion)  +  ne M ( free metal )

Example: Zinc oxide ( ZnO ) is mixed with excess coke and heated at a temperature of about 1300 – 1400° C in a retort when zinc oxide is reduced to metallic zinc.

               ZnO + CZn + CO

44. How is zinc extracted by the carbon reduction process?

During zinc extraction by carbon reduction process, the zinc ore, i.e., zinc blende (ZnS) or calamine ( ZnCO₃) is converted into zinc oxide. Zinc oxide is then mixed well with excess coke powder. The mixture is then taken in a retort made of fireclay and heated at a temperature of about 1300 – 1400°C. At this temperature, zinc oxide is reduced to metallic zinc and carbon monoxide( CO ) is evolved.

                   ZnO + C Zn + CO

45. How are the metals placed at the top of the metal activity series extracted?

These metals are usually extracted by electrolytic method. The molten hydroxide or chloride salts of the metal is electrolysed using suitable electrodes, and the metal deposits on the cathode.

For example, sodium is extracted by electrolysing a molten solution of sodium chloride using iron cathode and graphite anode. Sodium is deposited at the cathode.

Dissociation of NaCl:    NaCl (molten)Na⁺ + Cl^– 

Reaction at cathode:     Na⁺ + e Na

Reaction at anode:        Cl^– Cl + e ( oxidation )

                                        Cl + Cl Cl₂ ( reduction )

46. Describe the extraction of aluminium from pure Alumina by electrolytic method.

Aluminium is generally extracted from bauxite ore Al₂O₃ . 2H₂O. At first, bauxite is converted into pure alumina. Pure alumina is then mixed with a proportionate amount of cryolite ( CaF₂) and fluorspar ( AlF₃ . 3NaF ) and the mixture is heated at around 900°C. When electricity is passed through the fused mixture, aluminium is deposited at the cathode.

Electrolytic dissociation:  Al₂O₃ ( molten ) 2Al³⁺ + 3O^2-

Cathode reaction:  2Al³⁺ + 6e 2Al

Anode reaction:     3O^2- 3O + 6e ;  3O + 3O 3O₂

47. Why are the strong electropositive metals like Na, K etc., not extracted from the aqueous solution of their salts.

An aqueous solution of a salt of a strong electropositive and metal contains H⁺ ions formed due to dissociation of water, along with the metal cations. Now, the tendency of H⁺ ions to be discharged at cathode is stronger than that of metals like Na, K etc. Hence, hydrogen gas will be produced at cathode instead of metal ions. Hence, hydrogen gas will be produced at cathode instead of desired metal. This is why a strong electropositive metal is extracted from its salt by electrolysis of the fused salt but not the aqueous solution of the salt.

48. To protect iron from rusting, which one between zinc plating and Tin plating is more effective and why?

When a crack on the surface of zinc plated iron exposes the metallic iron, the metallic iron remains unaffected by the action of moist air and does not corrode. This is because zinc is more reactive than iron( zinc is at a higher position than iron in metal activity series) and hence zinc is affected by moist air more readily than iron.

On the other hand, any crack on the surface of tin plated iron which exposes iron makes the iron part vulnerable to rusting. This is because iron is more reactive than tin and hence iron is affected by moist air more readily than tin.

This is why zinc plating is more effective in preventing Rust than tin plating.

49. Several magnesium blocks are attached to the bottom of the ship.Why?

The salty water of Seas and oceans accelerates the process of rusting. The magnesium blocks attached to the bottom of the ship to protect the iron parts of ships from rusting. Here, the ship acts as an electrochemical cell. Mg  is placed above iron in the metal activity series and hence, Mg acts as anode while iron acts as cathode. The salty water of the ocean acts as an electrolytic solution. As oxidation takes place at anode, Mg is preferably oxidised to Mg²⁺ ions. Thus iron remains unaffected as long as Mg blocks are present. New blocks replace the already attached blocks that get corroded.

50. Discuss the harmful effects of rusting.

1. Rusting affects the metallic lustre of iron.
2. Iron is used to prepare substances for household works, transportation, agricultural and defence instruments. This substance corrodes due to rusting causing huge economic losses.

51. Give some methods to prevent rusting of iron.

1. The iron articles can be protected from rusting by putting their surfaces with varnishes, Paints for Coal Tar
2. Resting can be prevented by electroplating iron with zinc, tin or chromium.
3. When steam is passed over red hot iron, a thin layer of ferrosoferric oxide ( Fe₃O₄) is formed on the surface of iron which protects it from rusting.
4. The underground oil pipeline through water, made of iron are protected by using Mg blocks.

52. Why do the oil or water pipelines through Oceans and seas tends to form rust readily? How are they protected from rusting?

Ocean and sea water contains dissolved Chloride and sulphate ions. These iron facilitates the process of rusting. Hence, oil or water pipelines through oceans and seas tend to form rust readily.

To protect the underground or underwater pipelines from rusting, a block of more electropositive metal ( like Mg ) is connected to the pipe through an insulated wire. When current is passed, the iron pipe acts as a cathode, the magnesium block as anode and water as electrolyte. Magnesium being more reactive than iron is readily oxidized and hence prevents iron from rusting. The Mg block needs to be replaced after sometime as it corrodes gradually.

53. Food or fruits having sour test should not be stored in containers made of aluminium, zinc or copper. Why?

Food or fruits having sour taste contain organic acids. These organic acids react with aluminium or zinc to form water soluble salts. Similarly, copper may also form water soluble salt with organic acids in the presence of oxygen. Some of the produce salts are toxic and may cause food poisoning. Hence, it is advisable not to store food or fruits having sour taste in containers made of aluminium, zinc or copper.

54. State two Important characteristics of alloys.

Some important characteristics of alloys are discussed below-

A) An alloy may be homogeneous or heterogeneous in nature.

b) An alloy had different characteristic properties than its constituent metals.

55. Name two alloys of iron and state their compositions. Mention some uses of this alloy.

Composition and uses of three alloys of iron are:

Alloy	Composition	Uses
Stainless steel	Fe: 73%, Cr:18%, Ni:8%,C:1%	In making utensils, knives, scissors, surgical instruments, machine parts etc.
Nickel steel	Fe: 96-98%, Ni: 2-4%	Manufacturing Automobile parts, gear, propeller of aircrafts, cables etc.

56. Give the composition and uses of two alloys containing both Copper and Zinc as their constituents.

Alloy	Composition	Uses
Brass	Cu: 60-80%, Zn:20-40%	Making parts of telescope, barometer etc., utensils,pipes,statues etc.
Bronze	Cu: 80% , Sn: 18%, Zn: 2%	Making statues, coins, utensils, medals etc.

57. Describe the principle of thermite process with an example.

Al has a strong affinity for oxygen at high temperatures. When oxides of relatively less reactive metals such as Fe, Mn, Cr etc., are heated with Al powder at a very high temperature, the oxides are reduced by Al to the corresponding metal. This is the basic principle of Goldsmith’s thermite process. The process produces a large amount of heat and the reaction temperature reaches as high as 2000°C. At this temperature, the extracted metal is obtained in a molten state.

58. State three advantages of Thermite Process.

1. Metal extraction by thermite process doesn’t require large machinery. Metals can be extracted on a small scale by this method for different purposes.
2. Broken parts of large machinery, rail line, Tram line, ships can be repaired by thermite process. But, it is not required to transport the damaged parts to the factories.
3. Huge quantity of Al₂O₃ is produced as a byproduct. This can be used for the preparation of emery powder used in metal polishing and manufacture of brick used in the inner layer of furnace.