Selina Concise Chemistry Class 10 ICSE Solutions Metallurgy

Selina Concise Chemistry Class 10 ICSE Solutions Metallurgy

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Selina ICSE Solutions for Class 10 Chemistry Chapter 7 Metallurgy

Exercise 7(A)

Solution 1.

Three classes in which elements are classified are:
Metals, Non-metals and Metalloids
Copper was the first metal used by man.

Solution 2.

(a) The metal which is a constituent of blood pigment is Iron (Fe)
(b) The metal which is a constituent of plant pigment is Magnesium (Mg).

Solution 3.

(a) Nitrogen: It is used to preserve food.
(b) Hydrogen: It is used in the hydrogenation of vegetable oils to make ghee.
(c) Carbon: It is essential for the growth and development of living beings.

Solution 4.

The metal which is present in abundance in earths crust is aluminium.
The non-metal which is present in abundance in the earth crust is oxygen.

Solution 5.

Metals are defined as the elements which form positive ions by the loss of electrons.
Non-metals are the elements which form negative ions by the gain of electrons.

Solution 6.

(a) Alkali metals: They are placed in IA group, the first column on the left of the periodic table.
(b) Alkaline earth metal: They are placed in IIA group, the second column on the left of the periodic table.
(c) Iron and Zinc: Fe is placed in VIII group and Cu is placed in IB group.
(d) Aluminium: It is placed in IIIA group present on the right of periodic table.

Solution 7.

(a) Alkali metals:-
(i) Bonding: All alkali metal salts are ionic in nature.
(ii) Action of air: The react rapidly with oxygen and water vapour in the air.
(iii) Action of water: They react violently with water and produce hydrogen gas.
2M + 2H2O → 2MOH + H2
(iv) Action of acid: They react violently with dil. HCl and dil. H2SO4 to produce hydrogen gas.
2M + 2HCl → 2MCl + H2

(b) Alkaline earth metal:-
(i) Bonding: All alkaline earth metal salts except beryllium are ionic compounds.
(ii) Action of air: They are less reactive than alkali metals.
(iii) Action of water: They react with water to produce hydrogen gas.
M + 2H2O → M(OH)2 + H2
(iv) Action of acid: They react with dilute HCl and dil. H2SO4 to produce hydrogen gas.
M + 2HCl → MCl2 + H2

Solution 8.

Elements which show properties of both metals and non-metals are called metalloids.
For example: Silicon, Germanium.

Solution 9.

Hydrogen is placed with alkali metals as it has one electron similar to the alkali metals.

Solution 10.

(a) Bromine
(b) Lead
(c) Gallium
(d) Carbon
(e) Sodium
(f) Sodium
(g) Tungsten
(h) Carbon fibre
(i) Carbon
(j) Mercury

Solution 11.

(i) Ion formation: Metals form positive ions by loss of electrons whereas non-metals form negative ions by gain of electrons.

(ii) Discharge of ions: Metals are discharged at the cathode during electrolysis whereas non-metals are liberated at the anode during electrolysis.

(iii) Nature of oxide formed: Oxides of metals are usually basic. Soluble basic oxides dissolve in water forming an alkaline solution whereas oxides of non-metals are usually acidic. Soluble acidic oxides dissolve in water forming an acidic solution.

(iv) Oxidizing and reducing property: Metals ionize by loss of electrons and hence are reducing agents whereas non-metals ionize by gain of electrons and hence are oxidizing agents.

(v) Reaction with acids: Metals above hydrogen in activity series usually replace hydrogen from dilute non-oxidising acids whereas non-metals do not react with dilute hydrochloric acid or sulphuric acid.

Solution 12.

(a) Na – e  → Na+
(b) N + 3e → N3-
(c) Cl + e → Cl
(d) Mg – 2e– → Mg2+
(e) M + 2HCl → MCl2 + H2
(f) Mg + H2SO4 → MgSO4 + H2

Solution 13.

(a) Fe2O3
(b) PbO
(c) Mn2O7
(d) NO

Solution 14.

Exercise 7(B)

Solution 1.

(a) Mercury and gallium
(b) Sodium and potassium
(c) Mercury
(d) Iodine
(e) Graphite
(f) Zinc
(g) Neon , Argon
(h) CrO3 , Mn2O7
(i) Al2O3,PbO
(j) Potassium , sodium
(k) Basic copper(II) sulphate
(l) Aluminium , Oxygen
(m) Hydrogen
(n) Carbon
(o) Iron

Solution 2.

(a) Occurrence of metals: The metals placed at the top of activity series are most reactive, so they always exist in the combined state whereas the metals placed below the activity series are least reactive, so they can be found in the isolated state also.

(b) Tendency to corrosion: The metals lying above the hydrogen in activity series can easily react with moisture and air and corrode easily whereas the metals such as gold and platinum do not corrode easily.

(c) Reaction with water: The ability of the metals to reduce water to hydrogen decreases on moving down the series.

Potassium and sodium reacts with cold water whereas magnesium reacts with warm water and aluminium, zinc and iron reacts with steam.

(d) Reaction with acids: All the metals above hydrogen, in the activity series, reduce hydrogen ions from dil. hydrochloric or sulphuric acid and give out hydrogen gas. The rate of reaction decreases on moving down the series.

Solution 3.

selina-icse-solutions-class-10-chemistry-metallurgy-7b-3

Solution 4.

The metals placed higher in the activity series (i.e. Na and K) are stable to heat and soluble in water.
Whereas metals like Ca, Mg, Al, Zn, Fe, Pb, Cu decompose on heating with decreasing vigour to form metal oxide and carbon dioxide.
The metals which lie below in the activity series (i.e. Hg, Ag) decompose on heating to form metal, oxygen and carbon dioxide.

Solution 5.

(a) Alkali metals like sodium and potassium are kept in kerosene as they react with moisture and air.
(b) (i) Basic lead carbonate is a mixture of lead hydroxide and lead carbonate.
(ii) Brown powder is mainly hydrated iron(III) oxide (Fe2O3.xH2O)

Solution 6.

Oxides of metals like Na, K, Ca, Mg, Al are stable to heat and so can be reduced only by electrolysis.
Zinc oxide can be reduced by coke only.
Oxides of iron, lead and copper are reduced by C, CO, H2 and NH3.
Oxides of mercury and silver decompose to give metal and oxygen.

Solution 7.

Metal A is more reactive than Metal B.
(a) Metal A is Na (Sodium). Metal B is Ca (Calcium).
Reaction with HCl:

selina-icse-solutions-class-10-chemistry-metallurgy-7b-7

(b) (i) Oxides: Sodium and calcium oxides are stable to heat.
(ii) Hydroxides: Sodium hydroxide is stable to heat whereas calcium hydroxide decomposes on heating to metal oxide and water vapour.
(iii) Carbonates: Sodium carbonate is stable to heat whereas calcium carbonates decompose on heating to form calcium oxide and carbon dioxide.
(iv) Nitrates: Sodium nitrate on heating form nitrite and oxygen whereas calcium nitrate decomposes on heating to form calcium oxide, nitrogen dioxide and oxygen.

Solution 8.

(a)

MetalsNon-metals

(i) Good conductors of heat
(ii) Malleable
(iii) Form positive ions
(iv) Form basic oxides

Poor conductors of heat
Non-Malleable
Forms negative ions
Form acidic oxides

(b) Valence electrons present in :
(i) Metals have 1, 2 or 3 valence electrons.
(ii) Non-metals have 5, 6 or 7 valence electrons.

Solution 9.

When the surface of metal is attacked by air, moisture or any other substance around it, the metal is said to corrode and the phenomenon is known as corrosion.
Necessary conditions for corrosion are:

  1. Presence of oxygen and moisture.
  2. Metals which are placed higher in the activity series corrode more easily.

Solution 10.

Conditions for increase of corrosion are:

  1. Presence of oxygen and moisture.
  2. Metals which are placed higher in activity series corrode more easily
  3. Dissolved salts in water act as electrolyte and enhance the rate of corrosion.
  4. The presence of pollutants like NO2and CO2increases rusting.

Solution 11.

Corrosion of metals is an advantage as it prevents the metal underneath from further damage. For example: On exposure to air, the surface of metal like aluminium and Zinc forms layers of their oxides which are very sticky and impervious in nature and hence act as protective layer. This layer protects the metal from further damage.

Solution 12.

Rusting is the slow oxidation of iron by atmospheric oxygen in the presence of water.
Equation:
4Fe + 3O2 + 2x H2O → 2Fe2O3.xH2O

Solution 13.

Two conditions necessary for rusting of iron are:

  1. Air
  2. Water

Solution 14.

By painting an iron object, the iron do not come in contact with atmospheric reagents .This prevents rusting.

Solution 15.

Galvanisation is the process of applying a protective zinc coating to steel or iron, in order to prevent rusting.
The zinc coating does not allow iron to come in contact with air and moisture and thus protects it from rusting.

Solution 16.

Silver gets tarnished when exposed to the atmosphere which contains pollutant H2S and forms a black coating of Ag2S.
Copper forms a green deposit on its surface when exposed to moist air. This is usually basic copper (II) sulphate.

Solution 17.

Aluminium forms white colour oxide on exposure to the atmosphere. This white colour oxide prevents it from further corrosion whereas iron reacts with air to form hydrated oxide called rust. So, iron undergoes corrosion to greater extent.

Solution 18.

The noble metals such as gold and platinum do not corrode easily.

Solution 19.

Gold is the most unreactive metal so it does not react with air or water and other gases in atmosphere. So gold does not corrode. That is why gold look new after several years of use.

Exercise 7(C)

Solution 1.

The process used for the extraction of metals in their pure form from their ores is referred to as Metallurgy.
The processes involved in Metallurgy are:

  1. Crushing and Grinding
  2. Concentration
  3. Roasting andcalcination
  4. Reduction
  5. Refining

Solution 2.

(a) A metal which occurs as sulphide is lead.
(b) A metal which occurs as halide is silver.
(c) A metal which occurs as carbonate is zinc.
(d) A metal which occurs as oxide is iron.

Solution 3.

(a) Minerals are naturally occurring compounds of metals which are generally present with other matter such as soil, sand, limestone and rocks. Ores are those minerals from which the metals are extracted commercially at low cost and comfortably. All ores are minerals, but all minerals are not necessarily ores.

(b) Ores are those minerals from which the metals are extracted commercially at low cost and with minimum effort. A metallic compound is a compound that contains one or more metal elements. Examples: AgNO3 – Silver nitrate is a metallic compound.

Solution 4.

The metals that can be extracted from the following ores are:
(a) Bauxite- Aluminium
(b) Calamine- Zinc
(c) Haematite- Iron

Solution 5.

Three objectives achieved during the roasting of ores is:

  1. It removes moisture from ores.
  2. It makes the ore porous and more reactive.
  3. It expels volatile impurities.
  4. It convertssulphideores into oxides.

Solution 6.

(a) Hydraulic washing: The difference in the densities of the ore and the gangue is the main criterion.
(b) Forth floatation: This process depends on the preferential wettability of the ore with oil and the gangue particles by water.
(c) Electromagnetic separation: Magnetic properties of the ores.

Solution 7.

(a) The processes involved in

(i) Processes involved in concentration are:

  1. Hydrolytic method
  2. Magnetic Separation
  3. Froth floatation
  4. Leaching

(ii) Processes involved in Refining of ores are:

  1. Distillation
  2. Liquation
  3. Oxidation
  4. Electro- refining

(b) Potassium and sodium oxides cannot be reduced by carbon, carbon monoxide and hydrogen.

Solution 8.

(a) Flux: A flux is a substance that is added to the charge in a furnace to remove the gangue.
(b) Gangue: Earthly impurities including silica, mud etc., associated with the ore are called gangue.
(c) Slag: It is the fusible product formed when flux reacts with impurities during the extraction of metals.
(d) Smelting: Smelting is the process of reducing the roasted oxide ore and removing the gangue with the help of an appropriate flux added with the ore.

Solution 9.

Iron and zinc are quite reactive and hence they do not occur in the free state. The compounds of metals found in nature are their oxides, carbonate and sulphides.

Solution 10.
selina-icse-solutions-class-10-chemistry-metallurgy-7c-10

Solution 11.
selina-icse-solutions-class-10-chemistry-metallurgy-7c-11

Solution 12.

selina-icse-solutions-class-10-chemistry-metallurgy-7c-12

Solution 13.

Oxides of highly active metals like potassium, sodium, calcium, magnesium and aluminium have great affinity towards oxygen and so cannot be reduced by carbon or carbon monoxide or hydrogen.

Metals in the middle of activity series (iron, zinc, lead, copper) are moderately reactive and are not found in oxide form. These are found in nature as sulphides or carbonate. These are first converted into oxides and can be reduced by C, CO or H2.
selina-icse-solutions-class-10-chemistry-metallurgy-7c-13
Metals low in the activity series is very less reactive and oxides of these metals are reduced to metals by heating alone.

Solution 14.

selina-icse-solutions-class-10-chemistry-metallurgy-7c-14

Solution 15.

Aluminium has a great affinity towards oxygen and so cannot be reduced by carbon or carbon monoxide. So it is extracted from its oxide by electrolysis.
Metals like copper, lead and iron are placed in the middle of the activity series and re moderately reactive and their oxides can be reduced by carbon, CO and hydrogen.
Mercury and silver are less reactive and are placed lower in the reactivity series. The oxides of these metals are reduced to metals by heating their oxides.

Solution 16.

The process used for the concentration of the ore is froth floatation process.

Solution 17.

(a) The purification depends upon:

  1. Nature of metal.
  2. Nature of impurities present in the metal.
  3. Purpose for which metal is to be used

(b) Methods used for purification are:

  1. Distillation
  2. Liquation
  3. Oxidation
  4. Electro-refining

(c) The impure metal is made the anode, while a thin sheet of pure metal is made the cathode. Electrolyte used is a salt solution of a metal which is to be refined. Pure metal deposits at the cathode and impurities settle down forming anode mud.

selina-icse-solutions-class-10-chemistry-metallurgy-7c-17

Solution 18.

selina-icse-solutions-class-10-chemistry-metallurgy-7c-18

Exercise 7(D)

Solution 1.

Position in the Periodic Table: Period 3,Group IIIA(13)

Solution 2.

selina-icse-solutions-class-10-chemistry-metallurgy-7d-2

Solution 3.

Bauxite ore contains approximately 60% aluminium oxide. The rest being sand, ferric oxide and titanium oxide.

Solution 4.

Red mud consists of ferric oxide, sand etc. left after bauxite dissolves in NaOH forming sodium aluminate and is removed by filtration.

Solution 5.

As aluminium has great affinity for oxygen, so it is stable compound. It is not easily reduced by common reducing agents like carbon, carbon monoxide or hydrogen. Hence, electrolytic reduction is chosen as the method for reducing alumina.

Solution 6.

selina-icse-solutions-class-10-chemistry-metallurgy-7d-6

Solution 7.

(a) The process by which refining of aluminium is done is called Hoope’s electrolytic process.
(b) Molten impure aluminium forms the bottom layer. The bottom layer has carbon lining and serves as anode.
Pure molten aluminium with carbon electrodes serves as cathode in top layer.
(c) Reactions at the two electrodes are:
Anode: Al -3e → Al3+
Cathode: Al3+ + 3e → Al

Solution 8.

Reaction of aluminium:

(a) Air: Aluminium forms oxide at room temperature.
Aluminium powder burns in air at about 8000C forming its oxide and nitride with a bright light.
4Al + 3O2 → 2Al2O3
2Al + N2 → 2AlN

(b) Water: Water has no action on aluminium due to layer of oxide on it.
When steam is passed over pure heated aluminium, hydrogen is produced.
2Al + 3H2O → Al2O+ 3H2

(c) Acid: It reacts with acids to produce salt and hydrogen.
2Al + 6HCl → 2AlCl3 + 3H2
Dilute sulphuric acid reacts with metal to liberate hydrogen.
2Al + 3H2SO4 (dilute) → Al2(SO4)3 + 3H2

Concentrated sulphuric acid reacts with aluminium to produce sulphur dioxide.
2Al + 6H2SO4 → Al2(SO4)3 + 6H2O + 3SO2
Dilute and concentrated nitric acid does not attack the metal aluminium.

(d) Base: Aluminium reacts with boiling and dilute alkalies to produce meta aluminate while with fused alkali produce aluminate.
2Al+ 2NaOH +2H2O → 2NaAlO2 +3H2
(Sodium meta aluminate)
2Al + 6NaOH → 2NaAlO3 +3H2
(Sodium aluminate)

Solution 9.

The role of cryolite in the electrolytic reduction of alumina in Hall’s process is :

  1. Lowers the fusion temperature from 20500C to 9500C and enhances conductivity.
  2. Increases its conductivity since pure alumina is almost a non-conductor of electricity.
  3. Cryoliteacts as a solvent for the electrolytic mixture.

Solution 10.

(a) Aluminium is more active metal but it gets oxidized and forms a thin protective layer on its surface which prevents further corrosion.
(b) Aluminium vessels should not be cleaned with powders containing alkalis because it results in the formation of meta aluminates and hydrogen.
2Al + 2NaOH + 2H2O → 2NaAlO2 + 3H2

Solution 11.

selina-icse-solutions-class-10-chemistry-metallurgy-7d-11-1
selina-icse-solutions-class-10-chemistry-metallurgy-7d-11-2
selina-icse-solutions-class-10-chemistry-metallurgy-7d-11-3
(c) A layer of aluminium is formed on iron at high temperature during cooking and food becomes deficient in iron.

Solution 12.

(a) In the electrolytic reduction of alumina, the graphite (anode) is oxidized by oxygen to CO and further forms CO2, so it is consumed and has to be replaced from time to time.
2C + O2 → 2CO
2CO + O2 → 2CO2

(b) Roasting provides oxygen to convert metallic sulphides into metallic oxide and SO2 which takes place when heated in excess of air.
Carbonate is converted into oxide by loss of CO2 which takes place in the absence of air and when heated strongly.

(c) Aluminium has a great affinity towards oxygen and so cannot be reduced by carbon or carbon monoxide or hydrogen whereas lead oxide can be easily reduced to metal lead by carbon.
PbO + C → Pb + CO

Solution 13.

(a) Flux combines with the gangue to form a fusible mass called slag.
(b) It forms slag[CaSiO3] with silica.
(c) It is removed from upper outlet, slag being lighter float on molten iron.

Solution 14.

(a) Froth flotation process: Zinc blende[ZnS]
(b) Magnetic Separation: Haematite[Fe2O3]

Solution 15.

Electrolytic Reduction

  1. It is removal of oxide or halide from a metal.
  2. Oxides of highly active metals like Na,K,Ca,Mg,Al are reduced by electrolytic reduction of their fused salts.
  3. Oxides of these metals have great affinity for oxygen than carbon and cannot be reduced by carbon or CO or hydrogen.

Electrolytic refining of metals is the separation of residual impurities like Si and phosphorus.

  1. Presence of other metals and non-metals like Si and phosphorus.
  2. Unreduced oxides and sulphides of metals.

It depends upon:

  1. Nature of metal
  2. Purpose for which metal is to be obtained.
  3. Nature of impurities present.
  4. Impure metal is made anode while a thin sheet of pure metal is made cathode and electrolyte used is a salt of solution of a metal to be refined.

Solution 16.

The three ways in which metal zinc differs from the non-metal carbon is:

  1. Zinc has avalency2 and carbon has valency 4.
  2. Zinc does not form hydride but carbon does (CH4).
  3. Oxides of zinc areamphoteric(ZnO) whereas oxides of carbon are acidic (CO2) and neutral (CO).

Exercise 7(E)

Solution 1.

(a) To prevent from rusting.
(b) Due to strong electropositive nature, it easily forms Zn+2 ions.
(c) Antiseptic in face creams.

Solution 2.

(a) Aluminium:

  1. Being a strong, light and corrosion resistant metal, it is used in alloys.
  2. Aluminium is light, it has high tensile strength, is resistant to corrosion, good conductor of heat, unaffected by organic acids and has attractive appearance. So it is used for making cooking utensils, in building and construction work.
  3. Aluminium has a strong affinity for oxygen so it is used as a deoxidizer in the manufacture of steel.

(b) Zinc:

  1. Zinc has a strong electropositive character, so it is used for coating iron and steel sheets to prevent them from rusting and this process is known as galvanization.
  2. Due to strong electropositive nature, it forms Zn+2ions, so it is used to make dry cell containers which act as negative electrode.
  3. Zinc act as a reducing agent for many organic reductions and these reductions are employed in manufacturing drugs, dyes.

Solution 3.

(a) Zinc is electropositive metal than iron, gets oxidized and saves iron. Also zinc forms protective layer of ZnO on iron. This layer is sticky and impervious in nature and protects the iron metal underneath from rusting.

(b) A neutral gas other than oxygen which is formed at anode during electrolysis of fused alumina is carbon monoxide.

(c) Nitric acid can be stored in aluminium containers as the dilute and conc. nitric acid does not react with aluminum. It renders aluminium passive due to the formation of an oxide film on its surface.

Solution 4.

(a) Cast iron: It is used in drain pipes, gutter covers, weights and railings.
(b) Wrought iron: It is used in chains, horse shoes and electromagnets.
(c) Mild steel: It is to manufacture nuts, bolts etc.
(d) Hard steel: It is used to make tools.

Solution 5.

(a) Galvanized iron sheets
(b) Zinc
(c) Zinc

Solution 6.

(a) Aluminium being strong, light and corrosion resistant metal is used for making alloy.
(b) Aluminium is light, malleable and does not rust so it is used for wrapping chocolates.
(c) To prevent them from rusting.
(d) It is used in aluminothermy as it is a good reducing agent.
(e) As aluminium forms a film of aluminium oxide, it protects the ships from corrosion. So it is used for making ships.

Solution 7.

(a) A mixture of 3 parts of ferric oxide (Fe2O3) and one part of aluminium powder (Al).
(b) A mixture of Potassium chlorate and magnesium powder is the ignition mixture.
(c) Fe2O3 + 2Al → Al2O3 + 2Fe + heat

Solution 8.

Alloy is a homogeneous mixture of two or more metals or of one or more metals with certain non-metallic elements.
The properties of alloys are often greatly different from those of the components.
For example: Gold is too soft to be used without small percentage of copper.
A low percentage of molybdenum improves the toughness and wear resistance of steel.
Bell metal is more sonorous than copper or tin.
Alnico an alloy of aluminium, nickel and cobalt can lift 60 times its own mass.
These added elements improve hardness, wear resistance, toughness and other properties.

Solution 9.

Alloy’s nameCompositionUses
1. Stainless steel73% Fe, 18%Cr,8%Ni,1%CUsed for making utensils, cutlery, ornamental pieces and surgical instruments.
2. Manganese steel85% Fe,1%C ,14%MnUsed for making rock drills and armour plates.
3. Tungsten steel84%Fe, 5%W, 1%CUsed for cutting tools for high speed lathes.

Solution 10.

The other element in Brass is Zinc.
The other elements in Bronze are Tin and Zinc.

Solution 11.

(a) Duralumin
(b) Solder
(c) Brass
(d) Zinc amalgam

Solution 12.

A mixture or an alloy of mercury with a number of metals or an alloy such as sodium, zinc, gold and silver as well as with some non-metals is known as amalgam.
Dental amalgam is a mixture of mercury and a silver tin alloy.

Solution 13.

(a) Two properties of brass that make it more useful than its components are:

  1. It is malleable and ductile.
  2. It resists corrosion.
  3. Can be easily cast.

(b) A metal which forms a liquid alloy at ordinary temperature is sodium.

Solution 14.

Magnalium is an alloy of aluminium with composition 90-95% and magnesium with composition 10-5%. It is used for making aircrafts.

Solution 15.

The constituents of
(a) Duralumin are aluminium (95%), copper (4%), magnesium (0.5%) and manganese (0.5%).
(b) Solder are lead (50%) and tin (50%).
(c) Bronze are copper (80%), tin (18%) and zinc (2%).
(d) Invar are iron (63%), nickel (36%) and carbon (1%).

Miscellaneous Exercise

Solution 1.

(a) Bauxite: Aluminium is extracted from its main ore bauxite Al2O3.2H2O. It contains 60% Al2O3.
(b) Sodium hydroxide: Sodium hydroxide dissolves bauxite to form sodium meta aluminate, removes insoluble impurities from Al2O3 by forming red mud.

selina-icse-solutions-class-10-chemistry-metallurgy-mis-1

Solution 2.

(a) Copper
(b) Iron
(c) Zinc
(d) Magnesium

Solution 3.

Arrangement of metal in decreasing order of reactivity are:
Sodium > Magnesium > Zinc > Iron > copper

Solution 4.

selina-icse-solutions-class-10-chemistry-metallurgy-mis-4
(iii) In electrolytic process, the graphite acts as anode. The anode has to be replaced from time to time as it gets oxidized by the oxygen evolved at the anode.
(iv) The reaction that occurs at cathode is:
4Al3+ + 12e → Al
(d) In construction the alloy of aluminium -duralumin is used because it is hard and resistant to corrosion.

Solution 5.

selina-icse-solutions-class-10-chemistry-metallurgy-mis-5
(d) In Aluminium thermite welding, the reduction with aluminium is highly exothermic and heat generated is sufficient to melt the metal.
Fe2O3 + 2Al → 2Fe + Al2O3 + Heat

Solution 1 (2005).

(i)

  1. Zinc: Froth Flotation, ZincBlende,Coke
  2. Aluminium: Bauxite,Cryolite, Sodium hydroxide solution

(ii)

  1. Sodium hydroxide.
  2. Cryolite

(iii) The formula of Cryolite is Na3AlF6.

Solution 1 (2006).

(a) Mercury
(b) Roasting
(c) CaSiO3
(d) Cryolite
(e) Graphite

Solution 1 (2007).

Acidic oxide(D)
Discharged at anode (F)
Covalent chlorides (I)
5,6,7 valence electrons (L)
Brittle(C)

Solution 1 (2008).

(i) A is made of carbon and B is thick graphite rod.
A → Cathode
B → Anode
(ii) Aluminium is formed at electrode A.
(iii) The two aluminium compound in the electrolyte C is Na3AlF6, Al2O3.
(iv) It is necessary to continuously replace electrode B from time to time as it gets oxidized by the oxygen evolved.

Solution 2 (2005).

(a) Stainless steel : Iron, Chromium
(b) Brass: Copper , Zinc

Solution 2 (2007).

selina-icse-solutions-class-10-chemistry-metallurgy-mis-2-2007

Solution 2 (2008).

Brass is an alloy of copper and Zinc.

More Resources for Selina Concise Class 10 ICSE Solutions

What is the Process of Metallurgy

What is the Process of Metallurgy

The various steps used in metallurgy are listed below.
1. Enrichment or dressing of the ore
2. Conversion of the enriched ore into the oxide of metal
3. Extraction of metal from the metal oxide
4. Refining or purification of the metal
Enrichment or dressing of an ore :
An ore mined from the earth’s crust contains a number of impurities (gangue), which must be removed. The ore, free from gangue, then becomes suitable for subsequent treatment. Enrichment or dressing of an ore is carried out by the following methods.
(i) Levigation : The powdered ore is washed in a jet of water. The lighter, rocky and earthy impurities are washed away by water, while heavier ore particles are left behind to settle down at the bottom. This process is also called hydraulic washing.
What is the Process of Metallurgy 1
(ii) Froth floatation : Sulphide ores of copper, lead and zinc are generally concentrated by this method.
What is the Process of Metallurgy 2The finely powdered ore is mixed with water and a small amount of oil in a tank. Air is blown into the mixture. A froth or scum is produced at the surface. The ore particles are carried by the froth to the surface. The earthy impurities sink to the bottom. The froth along with the ore is removed. An acid is added to break up the froth. The concentrated ore is filtered and dried.
(iii) Liquation : This process is used to concentrate the ore whose melting point is lower than that of the impurities. Stibnite, an ore of antimony, is concentrated by this method. The impure ore is heated. The ore melts and flows along the surface. The impurities are left behind.
(iv) Magnetic separation : This method is used when the magnetic properties of the ore and the impurities are different. For example, tinstone, an ore of tin, contains wolfram as an impurity that is magnetic. To remove this impurity, the ore is finely powdered to make the magnetic and the nonmagnetic particles distinctly separate. The powdered tinstone is spread on a belt moving over electromagnetic rollers in figure. The wolfram, being magnetic, is attracted and gets collected in the pot near the magnet. Tinstone falls away from the magnet.
What is the Process of Metallurgy 3(v) Leaching or chemical separation : In this method, the powdered ore is treated with a suitable solvent. The ore dissolves in it while the impurities remain undissolved. For example, the bauxite ore contains Fe2O3, SiO2, etc., as impurities. The ore is powdered and treated with a solution of sodium hydroxide. A12O3 and SiO2 present in the ore dissolve, forming sodium aluminate and sodium silicate respectively. The impurities are left behind undissolved. The impurities are filtered off. The filtrate containing sodium aluminate and sodium silicate is stirred with some freshly prepared aluminium hydroxide for several hours. Sodium aluminate undergoes hydrolysis producing aluminium hydroxide as precipitate. The addition of aluminium hydroxide accelerates the precipitation of hydroxide. Soluble sodium silicate remains in solution. The precipitate, when filtered, washed, dried and ignited, gives pure alumina (A12O3).

Al2O3 + 2NaOH  →  2NaAlO2 + H2O

NaAlO2 + 2H2O  →  Al(OH) + NaOH

2Al(OH)  →  Al2O3 + 3H2O
Conversion of the enriched ore into the oxide of metal

Conversion of the enriched ore into the oxide of metal

It is easier to obtain metals from their oxides than from their carbonates or sulphides. Hence, the concentrated ore is converted into the oxide of metal which is then reduced to metal. This conversion to oxide is done by the process of calcination or roasting. In this process the ore is heated very strongly in the absence of air, keeping the temperature below its melting point so that volatile impurities are driven off.
Examples:
(i) Oxide ores are calcined to remove moisture and other volatile impurities.

Al2O3 . 2H2O  →  Al2O3 + 2H2O

(ii) Carbonate ores are calcined to expel carbon dioxide.

CaCO3  →  CaO + CO2

CaC0. MgCO3  →  CaO + MgO + 2CO2

ZnC03  →  ZnO + CO2

CuCO3 . Cu(OH)  →  2CuO + H2O + CO2
Sulphide ores are usually converted to oxides by roasting. The process involves heating the ore at a temperature below its fusion point, but always in the presence of air so that it may be oxidized.
Arsenic and similar other elements present in free state or combined state are also oxidized to volatile oxides.
(i) Zinc blende (ZnS) is roasted in air to convert it into zinc oxide.

2ZnS + 3O2 → 2ZnO + 2SO2

(ii) Galena (PbS) is converted into litharge (PbO) by roasting.

2PbS + 3O2 → 2PbO + 2SO2

(iii) Cinnabar (HgS) is roasted to convert it directly into mercury (Hg).

HgS + O2 → Hg + SO2

(iv) Iron pyrite (FeS2) is converted into ferric oxide (Fe2O3) by roasting.

4FeS2 + 11O2 → 2Fe2O3 + 8SO2

Thus, both calcination and roasting produce oxide of the metal. However, there are a few points of difference between the two processes.

Calcination

Roasting

1.    The ore is heated in   the absence of air.

The ore is heated in the presence of air.
2.    It is used for oxide or   carbonate ores.

It is used for sulphide ores.

Chloride ores remains unchanged by calcination or roasting.

Extraction of metal from metal oxide :
A metal oxide thus produced is then reduced into metal. For this, the method used depends upon the reactivity of the metal being extracted. The following methods are used.
(i) Reduction by heat alone Metals occupying lower positions in the activity series can be obtained by heating their oxides.

2HgS + 3O2 → 2HgO + 2SO2

2HgO → 2Hg + O2

(ii) Chemical reduction Metals in the middle of the activity series (Fe, Zn, Ni, Sn, etc.) cannot be obtained by heating their compounds alone. They require to be heated with a reducing agent, usually carbon (coke). When a metal oxide is heated with carbon, it is reduced to free metal.

MO + C  →  M + CO      (M- Metal)

The reduction of metal oxides with carbon is known as smelting. The impurities are removed as slag.

Examples :

(i)   When zinc oxide is heated with carbon, zinc metal is obtained.

ZnO + C  →  Zn + CO

(ii)  When stannic oxide is heated with carbon, tin metal is produced.

SnO2 + 2C  →  Sn + 2CO

(iii) Ferric oxide (Fe2O3) is reduced to iron by heating with coke in a blast furnace.

Fe2O3 + 3C  →  2Fe  + 3CO

Reduction with aluminium (thermit process or alumino-thermic process)

Some metal oxides cannot be reduced satisfactorily by carbon. For them, aluminium, a more reactive metal, is used. The process is called thermic process or alumino-thermic process.

Examples :

(i)   Manganese dioxide is reduced to manganese by heating with aluminium.

3MnO2 + 4Al  →  3Mn + 2Al2O3

(ii) Ferric oxide (FeP3) is reduced by aluminium to free iron.

Fe2O3 + 2Al  →  2Fe + Al2O3

(iii) Chromium sesquioxide is reduced by aluminium to chromium metal.

Cr2O3 + 2Al  →  2Cr + Al2O3

In the thermit process, aluminium powder is mixed with metal oxide. A piece of magnesium is set alight to start the reaction. The aluminium reduces the oxide to free metal.

In case of iron oxide, iron is obtained in the molten state. (The mixture of iron oxide and aluminium powder is called thermite). The molten iron may be allowed to trickle down to weld two iron objects together. Cracked machine parts, railway tracks, etc., are joined by this method.
What is the Process of Metallurgy(iii) Electrolytic reduction : The reactive metals (high up in the activity series) cannot be produced by any of the above methods. They are obtained by electrolytic reduction of their molten oxides or chlorides. During electrolysis, the cathode supplies electrons to metal ions for their reduction to the metal.

Examples:

(i)  Sodium metal is obtained by the electrolysis of molten sodium chloride.
What is the Process of Metallurgy 5
(ii)  Magnesium metal is obtained by the electrolysis of molten magnesium.
What is the Process of Metallurgy 6
(iii)Aluminium oxide (Al2O3) is reduced to aluminium by the electrolysis of molten aluminium oxide.

 Al2O →  2Al3+ + 3O2–

The aluminium ions present in aluminium oxide go to the cathode and are reduced there to aluminium atoms.

Note : During electrolytic reduction of the molten salts, the metals are always liberated at the cathode.

(iv) Some specific methods Silver and gold are obtained by treating the ore with a solution of sodium cyanide. Sodium argentocyanide (in case of silver) or sodium aurocyanide (in case of gold) is obtained in the solution. On adding zinc dust to the solution, silver or gold is precipitated.

2Na[Ag(CN)2] + Zn  →  Na2[Zn(CN)4] + 2Ag

 2Na[Au(CN)2] + Zn  →  Na[Zn(CN)4] + 2Au

Refining of Metals :

The metal obtained from the ore is not pure. It contains various substances as impurities. The process of removing these impurities is called refining of the metal. Some of the methods generally applied for refining metals are discussed below.

1. Liquation : This process is used to separate metals of low melting points (e.g., tin and lead) from the metals of high melting points. 
What is the Process of Metallurgy 7In this process, a sloping hearth is used. The hearth is kept at a temperature a little above the melting point of the metal. The impure metal is placed at the top of the hearth. The metal melts and flows down the hearth. The infusible impurities are left behind. This method is used in the purification of tin.

2. Cupellation : This method is used to purify silver, containing lead as an impurity. The impure silver is heated in the presence of air in a vessel made of bone-ash. This vessel is called cupel. Lead is oxidized to lead monoxide. Most of the lead monoxide is carried away in the blast of air. The remaining portion of the lead monoxide melts and is absorbed by the bone-ash. Pure silver is left behind.

3. Poling :Copper is purified by this method. The molten impure copper (called blister copper) is stirred thoroughly with poles of green wood. The gases escaping from the poles reduce the oxide of metal to the metal. The surface of the molten copper is kept covered with powdered charcoal so that copper may not be reoxidized in contact with air.

4. Electrolytic refining : This method is widely used for purification of metals. Several metals such as aluminium, copper, tin, lead, gold, zinc and chromium are purified by this method. The impure metal is made the anode while a strip of pure metal acts as the cathode. A solution of the salt of the metal acts as the electrolyte.
What is the Process of Metallurgy 8On passing electric current through the solution, pure metal gets deposited on the cathode. The more reactive impurities present in the metal to be purified go into solution and remain there. The less reactive impurities fall to the bottom of the electrolytic cell.

Ultra-pure Metals :

In the present age of technological advancement, metals of high purity are required for special purposes. For example, pure germanium is needed for semiconductor devices. Uranium of high-grade purity is used as fuel in nuclear reactors.

Two special techniques have been devised to prepare metals of very very high purity.

1. Van Arkel method  : This method was developed by van Arkel to obtain ultra-pure metals. It is based on the thermal decomposition of metal compounds. It is used for obtaining pure titanium which is used in space technology. The impure titanium metal is converted into titanium tetra-iodide.

The air in the barrel used in this process is removed to create a high vacuum. An iodine bulb is broken. Titanium metal is heated which reacts with iodine to form gaseous titanium tetra-iodide.

Ti + 2I2 → TiI4

The impurities do not react with iodine. The vapour of titanium tetra-iodide is passed over a heated tungsten filament (1674 K). Titanium tetra-iodide gets decomposed into titanium and iodine. Pure titanium is deposited upon the filament and can be removed. The regenerated iodine can be reused to react with more titanium. The process is repeated.

2. Zone refining method : This method is capable of producing metals of high purity. Germanium, which is used in semiconductor devices, is purified by this method. In this method, advantage is taken of the fact that impure molten metal, when allowed to cool, deposits crystals of pure metal.
What is the Process of Metallurgy 9An impure germanium rod is provided with a circular heater. The heater is slowly moved along the metal rod. A band of the rod melts. As the heater moves away, the metal crystallizes out of the melt. The impurities are swept along the molten zone. Finally, the impurities reach the other end of the rod, and are removed.

Metallurgy

Metallurgy

The process of extracting metals from their ores and refining them for use is known as metallurgy. In other words, the process of obtaining a metal from its ores is called metallurgy of the metal.
Common terms used in discussing metallurgical operations :
1. Charge : The mixture of materials fed to a furnace for obtaining the metal is called charge.
2. Dressing of the ore : The removal of impurities associated with ore is called dressing or enrichment of the ore.
3. Calcination : The process of heating a metal-rich ore to a high temperature to convert the metal into its oxide, either in absence or insufficient supply of air is called calcination.
4. Roasting : The process of heating a finely ground ore to a high temperature in excess of air is called roasting. Roasting converts the metal present in the ore to its oxide.
5. Flux : A flux is a substance that is mixed with the fumance charge (calcined or roasted ore and coke) to remove the infusible impurities present in the ore.
6. Slag : Flux combines with the infusible impurities to convert them into a fusible substance called slag. Being light, slag floats over the molten metal and is removed from there.
Impurities present in metal oxides may be acidic or basic. For acidic impurities, such as SiO2 or P2O5, a basic flux (e.g., CaO) is added to the charge. If basic impurities such as MnO are present, silica is added to the charge.

ImpurityFluxSlag
SiO2       +CaO  →CaSiO3
P2O5       +3CaO   →Ca3(PO4)2
MnO       +SiO2  →MnSiO3

7. Gangue or matrix : The ore mined from the earth’s crust contains some unwanted substances or impurities, such as sand, rocky or clayey materials. These substances are called gangue or matrix. The gangue has to be removed before the process of extraction of metals starts.
8. Smelting: The process of obtaining the metal by reducing its oxide ore with coke is known as smelting.
Principles of metallurgy
The extraction of a metal from its ore depends upon the reactivity of the metals.
1. Metals at the top of the activity series (K, Na, Ca, Mg, etc.) are highly reactive. They do not occur in the free state. They are extracted by the electrolysis of the molten ore.
2. Metals in the middle of the activity series (Zn, Fe, Pb, etc.) are moderately reactive. These are obtained by roasting and calcination of their sulphide or carbonate ore.
3. Metals at the bottom of the activity series (Au, Ag, Pt, Cu) being the least reactive are found in the free state. Copper and silver also occur as their sulphide or oxide ores. These are obtained by the process of roasting.