ICSE Solutions for Chapter 7 Metallurgy Class 10 Selina Chemistry

Exercise 7 A

Question 1: Name the three classes in which elements are classified. Which was the first metal used by man?

Solution 1: Three classes in which elements are classified are:
Metals, Non-metals and Metalloids
Copper was the first metal used by man.

Question 2: Name the metal which is a constituent of (a) Blood pigment, (b) plant pigment

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).

Question 3: Give the importance of the following in living beings:
(a) Nitrogen, (b) Hydrogen, (c) carbon

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.

Question 4: Name the metal and non-metal present in abundance in the earth crust.

Solution 4: The metal which is present in abundance in earth crust is aluminium. The non-metal which is present in abundance in the earth crust is oxygen.

Question 5: Define metal and non-metal on the basis of electron loss or gain.

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.

Question 6: State the position of the following in the periodic table:
(a) Alkali metals, (b) Alkaline earth metals (c) Iron and zinc (d) Aluminium

Solution 6: (a) Alkali metals: They are placed in the IA group, the first column on the left of the periodic table.
(b) Alkaline earth metal: They are placed in the 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 the IB group.
(d) Aluminium: It is placed in the IIIA group present on the right of the periodic table.

Question 7: Give the general characteristics of
(a) Alkali metals,
(b) Alkaline earth metals with reference to
(i) bonding (ii) action of air (iii) action of water (iv) action of acid

Solution 7: (a) Alkali metals:
(i) Bonding: All alkali metal salts are ionic in nature.
(ii) The action of air: The react rapidly with oxygen and water vapour in the air.
(iii) The 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) The action of air: They are less reactive than alkali metals.
(iii) The 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

Question 8: What are metalloids: Give examples.

Solution 8: Elements which show properties of both metals and non-metals are called metalloids.
For example: Silicon, Germanium.

Question 9: Why is hydrogen placed with alkali metals?

Solution 9: Hydrogen is placed with alkali metals as it has one electron similar to the alkali metals.

Question 10: Name:
(a) a liquid non-metal,
(b) a metal with dull appearance
(c) a metal with low melting and boiling points
(d) a non-metal with high m.p & b.p
(e) a metal which can float on water
(f) a metal which can be cut with a knife.
(g) a metal which is a bad conductor of heat and electricity
(h) a non-metal which is ductile
(i) a non- metal used in alloys
(j) a non-malleable metal

Solution 10: (a) Bromine
(b) Lead
(c) Gallium
(d) Carbon
(e) Sodium
(f) Sodium
(g) Tungsten
(h) Carbon fibre
(i) Carbon
(j) Mercury

Question 11: Distinguish between metals and non-metals on the basis of (i) ion formation, (ii) discharge of ions, (iii) nature of oxide formed, (iv) oxidizing and reducing property, (v) reaction with acids.

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 a gain of electrons and hence are oxidizing agents.

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

Question 12:

Solution 12:

Question 13: Select from the following list:
Fe₂O₃, NO, PbO, Mn₂O₇
(a) Basic oxide...........
(b) Amphoteric oxide……..
(c) Acidic oxide..................
(d) Neutral oxide..........

Solution 13:
(a) Fe₂O₃
(b) PbO
(c) Mn₂O₇
(d) NO

Question 14: Take an element from alkali metal and one from an alkaline earth metal and write an equation for their action with:
(a) Hydrochloric acid, (b) Oxygen (c) Sulphuric acid (d) Water.

Solution 14: (a) Hydrochloric acid:
2Na + 2HCl ⟶ NaCl + H₂
Be + 2HCl ⟶ BeCl₂ + H₂

(b) Oxygen:
4Na + O₂ ⟶ 2Na₂O
Mg + O₂ ⟶ 2MgO

(d) Water
2Na + H₂O ⟶ 2NaOH + H₂
Mg + H₂O ⟶ Mg(OH)₂ + H₂

Exercise 7 B

Question 1: Name:
(a) Two metals which are liquid at room temperature
(b) two metals which are soft
(c) a metal which lacks ductility
(d) a non-metal which is lustrous
(e) a non-metal which conducts electricity
(f) a metal which is brittle
(g) two non-metals which are monoatomic
(h) two metallic oxides which are acidic
(i) two metallic oxides which are amphoteric
(j) two metals which react with cold water,
(k) the compound responsible for a green deposit on the surface of copper
(l) the most abundant metal and the most abundant non=metal
(m) a non-metal which can form a positive ion
(n) a non-metal which shows the reducing property
(o) a metal whose oxide is reduced only by carbon

Solution 1: (a) Mercury and gallium
(b) Sodium and potassium
(c) Mercury
(d) Iodine
(e) Graphite
(f) Zinc
(g) Neon, Argon
(h) CrO_3, Mn₂O₇
(i) Al₂O₃, PbO
(j) Potassium, sodium
(k) Basic copper(II) sulphate
(l) Aluminium, Oxygen
(m) Hydrogen
(n) Carbon
(o) Iron

Question 2: Explain how the activity series accounts for each of the following:
(a) occurrence of metals (b) tendency to corrosion (c) reaction with water (d) reaction with acids

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) The tendency to corrosion: The metals lying above the hydrogen inactivity 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 react with cold water whereas magnesium reacts with warm water and aluminium, zinc and iron react 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.

Question 3: Give balanced reactions for the following:
(a) Sodium is dropped in water
(b) Magnesium reacts with boiling water
(c) Red hot iron reacts with steam
(d) Iron reacts with dilute HCI

Solution 3:
2Na + 2H₂O ⟶ 2NaOH + H₂
Mg + H₂O ⟶ MgO + H₂
3Fe + 4H₂O ⇌ Fe₃O₄ + 4H₂
Fe + 2HCl ⟶ FeCl₂ + H₂

Question 4: Give a short account of the heating effect on metal carbonates based on the activity series.

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 a 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.

Question 5: (a) Why are alkali metals kept in kerosene oil?
(b) What is:
(i) basic lead carbonate and
(ii) brown powder deposit on iron?
(c) Why is hydrogen kept in the metal activity series?

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)

Question 6: Give the effect of heat on metal oxides based on the activity series.

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.

Question 7: Metal A has an electronic configuration of 2, 8, 1 and metal B has 2, 8, 8, 2 which is more reactive metal.
(a) Identify A and B and give their reactions with dil HCL and dil H₂SO₄
(b) Give the effect of heat on their:
(i) oxides (ii) hydroxide (iii) carbonates (iv) nitrates

Solution 7: Metal A is more reactive than Metal B.
(a) Metal A is Na (Sodium). Metal B is Ca (Calcium).
Reaction with HCl:
2Na + 2HCl ⟶ 2NaCl + H₂
Ca + 2HCl ⟶ CaCl₂ + H₂
Reaction with H₂SO₄:
2Na + H₂SO₄ ⟶ Na₂SO₄ + H₂
Ca + H₂SO₄ ⟶ CaSO₄+ H₂

(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.

Question 8: (a) The table below compares some properties of metals and non-metals. Write down the missing statements (i) to (iv):

(b) How many valence electrons are present in:
(i) metals
(ii) non-metals?

Solution 8:
(a)

Metals

Non-metals

(i) Good conductors of heat

(ii) Malleable

(iii) From positive ions

(iv) From basic oxides

(i) Poor conductors of heat

(ii) Non-malleable

(iii) Forms negative ions

(iv) 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.

Question 9: What is corrosion? What are the necessary conditions for corrosion?

Solution 9: When the surface of the 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.

Question 10: State under what conditions corrosion is faster

Solution 10: Conditions for an increase of corrosion are:
1. Presence of oxygen and moisture.
2. Metals which are placed higher inactivity series corrode more easily
3. Dissolved salts in water act as an electrolyte and enhance the rate of corrosion.
4. The presence of pollutants like NO₂ and CO₂ increases rusting.

Question 11: Corrosion can be an advantage in some case. Explain

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 a protective layer. This layer protects the metal from further damage.

Question 12: What is rust? Give the equation for the formation of rust.

Solution 12: Rusting is the slow oxidation of iron by atmospheric oxygen in the presence of water. Equation:
4Fe + 3O₂ + 2xH₂O → 2Fe₂O₃.xH₂O

Question 13: State two conditions necessary for rusting of iron.

Solution 13: Two conditions necessary for rusting of iron are:
1. Air
2. Water

Question 14: How does the painting of an iron object prevent rusting?

Solution 14: By painting an iron object, the iron do not come in contact with atmospheric reagents. This prevents rusting.

Question 15: What is galvanization? How does it protect the iron from 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 the iron to come in contact with air and moisture and thus protects it from rusting.

Question 16: A student has been collecting silver coins and copper coins. One day she observed a black coating on silver coins and a green coating on copper coins. Which chemical phenomenon is responsible for these coatings? Write the names of black and green coatings.

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.

Question 17: Aluminium is said to be more reactive than iron, towards oxygen (or air) yet iron undergoes corrosion to a greater extent than aluminium. Explain.

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 a greater extent.

Question 18: Which metals do not corrode easily?

Solution 18: The noble metals such as gold and platinum do not corrode easily.

Question 19: Why do gold ornaments look new even after several years of use?

Solution 19: Gold is the most unreactive metal so it does not react with air or water and other gases in the atmosphere. So gold does not corrode. That is why gold look new after several years of use.

Exercise 7 C

Question 1: Define the term ‘metallurgy'. State the processes involved in metallurgy.

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 and calcination
4. Reduction
5. Refining

Question 2: Which metal occurs as:
(a) sulphide
(b) a halide
(c) a carbonate
(d) an oxide
Also, give the names of their respective ores

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.

Question 3: Distinguish between:
(a) a mineral and an ore,
(b) an ore and a metallic compound

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 comfortable. 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.

Question 4: Which metal can be extracted from each one of the following ores.
(a) bauxite (b) calamine (c) haematite

Solution 4: The metals that can be extracted from the following ores are:
(a) Bauxite - Aluminium
(b) Calamine- Zinc
(c) Haematite - Iron

Question 5: State three objectives achieved during the roasting of ores

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 converts sulphide ores into oxides.

Question 6: Give the principles of
(a) hydrolytic method,
(b) froth floatation
(c) electromagnetic separation

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.

Question 7: Name: (a) the processes involved in
(i) concentration
(ii) refining of ores
(b) two metallic oxides which cannot be reduced by carbon, carbon monoxide or hydrogen

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

Question 8: Explain the following terms:
(a) flux (b) gangue (c) slag (d) smelting

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.

(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.

Question 9: Why does iron or zinc not occur free in nature?

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.

Question 10: What do you observe when hydrogen is passed over heated copper oxide?

Solution 10: Black copper oxide is reduced to brown/red.

Question 11: Compare roasting and calcination

Solution 11: Comparison of roasting and calcination:

Question 12: (a) Name an ore of zinc.
(b) which process is applied to concentrate it?
(c) How is concentrated ore changes to oxide?

Solution 12: (a) Ore of zinc is zinc blende (ZnS).
(b) It is concentrated by Froth floatation process.
(c) The concentrated ore is changed into oxide by heating ZnS in excess of air.

Question 13: Some metallic oxides can be reduced by hydrogen, carbon and carbon monoxide and some cannot. explain

Solution 13: Oxides of highly active metals like potassium, sodium, calcium, magnesium and aluminium have a 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.

Metals low in the activity series is very less reactive and oxides of these metals are reduced to metals by heating alone.

Question 14: How are the following metallic oxides reduced. Write equations:
(a) Iron (II) oxide, (b) Zinc oxide

Solution 14: (a) Iron(II) oxide:
4FeO + O₂ → 2Fe₂O₃

(b) Zinc oxide is reduced by coke.

Question 15: State why aluminium is extracted from its oxide by electrolysis while copper, lead, iron by reducing agents and mercury and silver by thermal decomposition.

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.

Question 16: An ore on being heated in air forms sulphurous anhydride. Write the process used for the concentration of this ore.

Solution 16: The process used for the concentration of the ore is froth floatation process.

Question 17: (a) on which factors does purification of metals depend?
(b) name the methods used for purification
(c) How is electro-refining done?

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. The 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.

Question 18:

Solution 18: Balanced equations are:

Exercise 7 D

Question 1: State the position of aluminium in the periodic table.

Solution 1: Position in the Periodic Table: Period 3, Group IIIA(13)

Question 2: Give the chemical names and formulae of any three ores of aluminium.

Solution 2: The chemical names and formulae of the ores of aluminium

Question 3: Which impurities are present in bauxite.

Solution 3: Bauxite ore contains approximately 60% aluminium oxide. The rest being sand, ferric oxide and titanium oxide.

Question 4: What is red mud, how is it removed?

Solution 4: Red mud consists of ferric oxide, sand etc. left after bauxite dissolves in NaOH forming sodium aluminate and is removed by filtration.

Question 5: Why electrolytic reduction is done to obtain aluminium?

Solution 5: As aluminium has a great affinity for oxygen, so it is a stable compound. It is not easily reduced by common reducing agents like carbon, carbon monoxide or hydrogen. Hence, the electrolytic reduction is chosen as the method for reducing alumina.

Question 6: Give the ionization reactions of electrolyte used in Hall's process. write the reaction at the cathode and the anode. Why the anode has to be replaced in this process?

Solution 6: The ionization reactions of electrolyte in Hall's process.
1. Cryolite: Na₃AlF₆ ⇌ 3Na⁺ + Al³⁺ + 6F^-
2. Fluorspar: CaF₂ ⇌ Ca²⁺+ 2F^-
3. Alumina : Al₂O₃ ⇌ 2Al³⁺ + 3O^2-
The reaction at the cathode and anode are:
Cathode: 4Al³⁺ + 12e^-➝ 4Al
Anode:
6O^2- - 12e^-➝ 6[O]
3O + 3O ➝ 3O₂
The anode has to be replaced from time to time as it gets oxidized by the oxygen evolved at the anode.

Question 7: (a) Name the process by which the refining of aluminium is done.
(b) Where are the cathode and anode in the electrolytic cell? Name the material used for these?
(c) state the reactions at the two electrodes.

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 a carbon lining and serves as an anode.
Pure molten aluminium with carbon electrodes serves as the cathode in top layer.

(c) Reactions at the two electrodes are:
Anode: Al - 3e^- ➝ Al³⁺
Cathode : Al³⁺ + 3e^- ➝ Al

Question 8: How does aluminium react with the following:
(a) Air, (b) Water, (c) Acid, (d) Base

Solution 8: Reaction of aluminium:
(a) Air: Aluminium forms oxide at room temperature.
Aluminium powder burns in air at about 800°C forming its oxide and nitride with a bright light.
4Al + 3O₂ ➝ 2Al₂O₃
2Al + N₂ ➝ 2AIN

(b) Water: Water has no action on aluminium due to the layer of oxide on it.
When steam is passed over pure heated aluminium, hydrogen is produced.
2Al + 3H₂O → Al₂O₃ + 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 → 2Na₃AlO₃ + 3H₂
(Sodium aluminate)

Question 9: What is the role of cryolite (Na₃AlF₆) in the electrolytic reduction of alumina in Hall's process?

Solution 9: The role of cryolite in the electrolytic reduction of alumina in Hall's process is:
1. Lowers the fusion temperature from 2050°C to 950°C and enhances conductivity.
2. Increases its conductivity since pure alumina is almost a non-conductor of electricity.
3. Cryolite acts as a solvent for the electrolytic mixture.

Question 10: (a) Aluminium is a more active metal than iron but suffers less corrosion. Why? (b) Explain and give reasons why aluminium vessels should not be cleaned with powders containing alkalis.

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 metal aluminates and hydrogen.
2Al + 2NaOH + 2H₂O → 2NaAlO₂ + 3H₂

Question 11: (a) Give the name and formula of the main area of iron and zinc
(b) How is the main ore of aluminium concentrated?
(c) Why 'the food containing iron salts’ should not be cooked in aluminium utensils?

Solution 11: (a) The main ores of iron and zinc are:

(b) Conversion of Impure Bauxite to Sodium aluminate

Impurities such as Fe₂O₃ and SiO₂ remain unaffected with conc. NaOH.
Conversion of Sodium aluminate to Aluminium hydroxide.

Conversion of Al(OH)₃ to pure Alumina.

(c) A layer of aluminium is formed on iron at high temperature during cooking and food becomes deficient in iron.

Question 12: Explain with reasons:
(a) In the electrolytic reduction of alumina, the graphite anode is gradually consumed.
(b) Roasting is carried out on sulphide ores and not on carbonate ores.
(c) Carbon can reduce lead oxide but not aluminium oxide

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

Question 13: (a) Why is flux used in the blast furnace?
(b) what does it form with silica present in the ore?
(c) How is it removed?

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 the upper outlet, slag being lighter float on molten iron.

Question 14: Name an ore which is concentrated by:
(a) froth floatation process,
(b) magnetic separation

Solution 14: (a) Froth flotation process: Zinc blende[ZnS]
(b) Magnetic Separation: Haematite[Fe₂O₃]

Question 15: Distinguish between electrolytic methods of reduction and refining.

Solution 15: Electrolytic Reduction
(i) It is the removal of oxide or halide from a metal.
(ii) Oxides of highly active metals like Na, K, Ca, Mg, Al is reduced by electrolytic reduction of their fused salts.
(iii) Oxides of these metals have a 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.
(i) Presence of other metals and non-metals like Si and phosphorus.
(ii) Unreduced oxides and sulphides of metals.

It depends upon:
(i) Nature of metal
(ii) Purpose for which metal is to be obtained.
(iii) Nature of impurities present.

Impure metal is made anode while a thin sheet of pure metal is made cathode and electrolyte used is a salt of the solution of a metal to be refined.

Question 16: Give three ways in which the metal zinc differs from the non-metals carbon. At least one of the differences must be a chemical difference.

Solution 16: The three ways in which metal zinc differs from the non-metal carbon is:
1. Zinc has a valency 2 and carbon has valency 4.
2. Zinc does not form hydride but carbon does (CH₄).
3. Oxides of zinc are amphoteric (ZnO) whereas oxides of carbon are acidic (CO₂) and neutral (CO).

Exercise 7 C

Question 1: State a reason why zinc is used in:
(a) galvanization,
(b) dry cells
(c) cosmetics?

Solution 1: (a) To prevent from rusting.
(b) Due to strong electropositive nature, it easily forms Zn⁺² ions.
(c) Antiseptic in face creams.

Question 2: State on what special properties the use of each of these metals depends:
(a) aluminium (b) zinc

Solution 2: (a) Aluminium:
(i) Being a strong, light and corrosion-resistant metal, it is used in alloys.
(ii) Aluminium is light, it has high tensile strength, is resistant to corrosion, good conductor of heat, unaffected by organic acids and has an attractive appearance. So it is used for making cooking utensils, in building and construction work.
(iii) 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 the negative electrode.
3. Zinc act as a reducing agent for many organic reductions and these reductions are employed in manufacturing drugs, dyes.

Question 3: Explain the following:
(a) zinc is used to cover iron so as to prevent rusting of iron why?
(b) A neutral gas other than oxygen which is formed at the anode during electrolysis of fused alumina
(c) Nitric acid can be stored in aluminium containers.

Solution 3: (a) Zinc is electropositive metal than iron, gets oxidized and saves iron. Also, zinc forms a 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 the 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 aluminium. It renders aluminium passive due to the formation of an oxide film on its surface.

Question 4: State the use of:
(a) cast iron (b) wrought Iron (c) Mild steel, (d) hard steel.

Solution 4:
(a) Cast iron: It is used in drain pipes, gutter covers, weights and railings.
(b) Wrought iron: It is used in chains, horseshoes and electromagnets.
(c) Mild steel: It is to manufacture nuts, bolts etc.
(d) Hard steel: It is used to make tools.

Question 5: Which metal is used for:
(a) making pipes, buckets, water tanks,
(b) lithographic plates for printing
(c) making face creams

Solution 5: (a) Galvanized iron sheets
(b) Zinc
(c) Zinc

Question 6: Give reasons, why aluminium is used in:
(a) making alloys
(b) wrapping chocolates
(c) painting electric and telegraphic poles
(d) In aluminothermic
(e) In making ships

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.

Question 7: Aluminum is used in thermite welding:
(a) what is thermit?
(b) what is the ignition mixture?
(c) write the reaction for the process?

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

Question 8: What is an alloy? How do the properties of an alloy differ from its constituents?

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.

Question 9: Name three alloys of steel. Give their compositions and uses.

Solution 9:

Alloy’s name	Composition	Uses
1. Stainless Steel	73% Fe, 18% Cr, 8% Ni, 1% C	Used for making utensils, cutlery, ornamental pieces and surgical instruments.
2. Manganese steel	85% Fe, 1% C, 14% Mn	Used for making rock drills and armour plates.
3. Tungsten steel	84% Fe, 5% W, 1% C	Used for cutting tools for high speed lathes.

Question 10: Both brass and bronze contain copper as major constituents Name other elements in these alloys.

Solution 10: The other element in Brass is Zinc.
The other elements in Bronze are Tin and Zinc.

Question 11: Name an alloy of:
(a) aluminium used in aircraft construction
(b) lead used in electrical wiring or electrical work in joining metals.
(c) copper in electrical appliances or household vessels (d) zinc used in simple voltaic cells

Solution 11: (a) Duralumin
(b) Solder
(c) Brass
(d) Zinc amalgam

Question 12: What is an amalgam? State its use with an example.

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.

Question 13: (a) state two properties of brass that render it more useful for some purpose than its components
(b) a metal which forms liquid alloys at ordinary temperature

Solution 13: (a) Two properties of brass that make it more useful than its components are:
(i) It is malleable and ductile.
(ii) It resists corrosion.
(iii) Can be easily cast.
(b) A metal which forms a liquid alloy at ordinary temperature is sodium.

Question 14: What is magnalium? Name the main elements present in it? Write its one use.

Solution 14: Magnalium is an alloy of aluminium with composition 90-95% and magnesium with composition 10-5%. It is used for making aircraft.

Question 15: Name the constituents of: (a) Duralumin (b) solder, (c) Bronze (d) Invar

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

Question 1: For each substance listed below, explain its significance in the extraction of aluminium.
(a) bauxite (b) Sodium hydroxide (c) Cryolite (d) Graphite

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.

(d) Graphite: Acts as cathode as well as anode.

Question 2: From the metals: copper iron, magnesium, sodium and zinc, select a different metal in each case which:
(a) does not react with dilute hydrochloric acid
(b) can form 2 + and 3 + ions
(c) has a hydroxide that reacts with both acids and alkalis
(d) for not react with cold water but reacts with steam when heated.

Solution 2: (a) Copper
(b) Iron
(c) Zinc
(d) Magnesium

Question 3: Arrange the metals in (2) in the decreasing order of reactivity.

Solution 3: Arrangement of metal in decreasing order of reactivity are:
Sodium > Magnesium > Zinc > Iron > copper

Question 4: In order to obtain 1 tonne of aluminium the following inputs are required. 4 tonnes of bauxite, 150 kg of sodium hydroxide and 600 kg of graphite. The aluminium compound in bauxite is aluminium oxide and the main impurity is iron (III) oxide, Aluminium is obtained by the electrolysis of aluminium oxide dissolved in cryolite (a) when bauxite is treated with sodium hydroxide solution, what happens to
(i) the aluminium oxide
(ii) the iron (III) oxide
(b) (i) Name the process used for the purification of bauxite
(ii) Write the equation for the action of heat on aluminium hydroxide
(c) (i) write the formulae of cryolite
(ii) Write down the word which correctly completes the following sentences. By dissolving aluminium oxide in cryolite a .............. (conducting/non conducting) solution is produced.
(iii) why is so much graphic required for the electrolytic process?
(iv) Write the equation for the reaction which takes place at the cathode.
(d) In construction work, why is the alloy of aluminium duralumin used rather than pure aluminium?

Solution 4: (a) (i) The aluminium oxide forms sodium aluminate.

(ii) The iron(III) oxide does not dissolve in NaOH and is removed by filtration.

(b) (i) The process used for the purification of bauxite is called Bayer's process.
(ii) The equation for the action of heat on aluminium hydroxide is: heat

(c) (i) The formula of the cryolite is Na₃AlF₆.
(ii) Conducting
(iii) In the electrolytic process, the graphite acts as an 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.

Question 5: Aluminium is extracted from its chief ore, bauxite. The ore is first purified and then the metal is extracted from it by electrolytic reduction
(a) Write three balanced equation for the purification of bauxite
(b) Name a chemical used for dissolving aluminium oxide, In which state of the subdivision is the chemical used?
(c) Write an equation for the reaction which takes place at the anode during the extraction of aluminium by the electrolytic process.
(d) Mention one reason for the use of aluminium in thermite welding.

Solution 5:
(a) Three balanced equations for purification of bauxite are:

(b) Fluorspar and cryolite are used for dissolving Al₂O₃. This chemical is used in the middle state.

(c) Reaction at anode:
6O^-2 - 12e^- → 6[O]
3O + 3O → 3O₂
Anode is oxidized to carbon monoxide and then to carbon dioxide.
2C + O₂ → 2CO
2CO + O₂ → 2CO₂

(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

Question 6: (a) A to F below relate to the source and extraction of either zinc or aluminium:
A. Bauxite
B. Coke
C. Cryolite
D. Froth floatation
E. Sodium hydroxide solution,
F. Zinc blende
(i) Write down the three letters each from the above list which are relevant to:
1. Zinc 2. Aluminium
(ii) Fill in the blanks using the most appropriate words from A to F.
1. The ore from which aluminium is extracted must first be treated with ................ So that pure aluminium oxide can be obtained.

Solution 6:
(i) 1. Zinc: Froth Flotation, Zinc Blende, Coke
2. Aluminium: Bauxite, Cryolite, Sodium hydroxide solution

(ii) 1. Sodium hydroxide.
2. Cryolite

(iii) The formula of Cryolite is Na₃AlF₆.

Question 7: Calcium copper, lead aluminium zinc chromium, magnesium and iron. Choose the major metals from the list given above to make the following alloys:
(a) Stainless steel
(b) brass

Solution 7: (a) Stainless steel : Iron, Chromium
(b) Brass: Copper , Zinc

Question 8: Name the following:
(a) A metal which is liquid at room temperature
(b) The process of heating an ore to a high temperature in the presence of air.
(c) The compound formed by the reaction between calcium oxide and silica
(d) A compound which is added to lower the fusion temperature of the electrolytic bath in the extraction of aluminium.
(e) Name an allotrope of a non-metal that allows electricity to pass through it.

Solution 8: (a) Mercury
(b) Roasting
(c) CaSiO₃
(d) Cryolite
(e) Graphite

Question 9: From the list of characteristics given below, select the five which are relevant to non-metals and their compounds:
A. ductile
B. Conduct electicity
C. Brittle
D. Acidic oxide
E. Basic oxides
F. Discharge at anode
G. Discharge at cathode
H. Ionic chlorides
I. Covalent chlorides
J. Reaction with dilute sulphuric acid yields hydrogen,
K. 1, 2, or 3 valence electrons
L. 5, 6, 7 valence electrons
(write the five letters corresponding to the correct characteristics)

Solution 9: Acidic oxide(D)
Discharged at anode (F)
Covalent chlorides (I)
5,6,7 valence electrons (L)
Brittle(C)

Question 10: The following is an extract from ‘Metals in the service of Man, Alexander and street/pelican 1976:
‘Alumina (aluminium oxide) has a very high melting point of over 2000° C so that it cannot readily be liquefied. However, conversion of alumina to aluminium and oxygen, by electrolysis can occur when it is dissolved in some other substance'. (i) Which solution is used to react with bauxite as a first step in obtaining pure aluminium oxide?
(ii) The aluminium oxide for the electrolytic extraction of aluminium is obtained by heating aluminium hydroxide. Write the equation for this reaction
(iii) Name the element which serves both as the anode and the cathode in the extraction of aluminium.
(iv) Write the equation for the reaction that occurs at the cathode during the extraction of aluminium by electrolysis.
(v) Give the equation for the reaction which at the anode when aluminium is purified by electrolysis.

Solution 10: (i) Sodium hydroxide
(ii)

(iii) Graphite

(iv) Reaction at cathode:
Al³⁺ + 3e^- → Al

(v) Reaction at anode:
Al - 3e^- → Al³⁺

Question 11: The following is a sketch of an electrolytic cell used in the extraction of aluminium: (i) What is the substance of which the electrodes A and B are made?
(ii) At which electrode (A or B) is the aluminium formed?
(iii) What are the two aluminium compounds in the electrolyte C?
(iv) why is it necessary for electrode B to be continuously replaced?

Solution 11: (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.

Question 12: Brass is an alloy of:
A. Copper and tin,
B. Copper and Zic
C. Zinc and leads,
D. Lead and tin.

Solution 12: Brass is an alloy of copper and Zinc.

ICSE Solutions for Chapter 7 Metallurgy Class 10 Selina Chemistry