Frank Solutions for Chapter 7 Metallurgy Class 10 Chemistry ICSE
1. Name the following:
(i) Two metals which are found in the free or native state.
(ii) The mixture of materials fed into a furnace to extract a metal.
(iii) The rocky impurities present in an ore.
(iv) The substance added to get rid of gangue in the extraction of metal.
(v) The process of heating a substance very strongly in such a way that it does not combine with oxygen.
(vi) The process in which an ore is heated in air so that oxygen gets added to it to form the oxides.
(vii) Ore of iron referred to as "fool's gold".
(viii) The chief ore of aluminium.
(ix) The substance added along with aluminium in the Hall-Heroult's process.
(x) The materials used as electrodes in the electrolytic extraction of aluminium.
(xi) The kind of welding in which aluminium powder is used.
(xii) The chief metal which occur in nature in free state as well as in combined state.
(xiii) The chief metal present in magnalium and duralumin
(xiv) Two metals which occur in nature in free state as well as in combined state.
(xv) Name two metals always find in combined state.
Answer
(i) Gold and Platinum.
(ii) Charge.
(iii) Gangue.
(iv) Flux.
(v) Calcination.
(vi) Roasting.
(vii) Iron pyrites.
(viii) Bauxite.
(ix) Cryolite, aluminium fluoride, Calcium fluoride.
(x) Cathode: inner lining of gas-carbon of the electrolytic cell.
Anode: Thick carbon rods dipping into the fused electrolytes.
(xi) Thermite welding.
(xii) Copper and silver.
(xiii) Aluminium, Iron.
(xiv) platinum and gold
(xv) sodium and potassium
2. Give reasons for the following:
(i) Zinc is used in galvanization and dry cells.
(ii) Nitric acid can be stored in aluminium containers.
(iii) Aluminium oxide cannot be reduced by carbon.
(iv) A neutral gas other than oxygen is formed at the anode during electrolysis of fused alumina.
(v) Extraction of aluminium was very difficult in the beginning.
(vi) Carbon anodes are used in the electrolytic extraction of aluminium.
(vii) Galvanized metal ions should not be used for storing food.
Answer
(i) Zinc is used in galvanization and dry cells because zinc coating protects the iron from corrosion as it is more electropositive than iron hence it would be attacked first.
(ii) Nitric acid can be stored in aluminium containers because it do not attack aluminium. It renders aluminium passive due to the formation of an oxide film on surface of aluminum.
(iii) Aluminium oxide cannot be reduced by carbon because it is comparatively high in electrochemical series hence more reactive than carbon.
(iv) A neutral gas other than oxygen is formed at the anode during electrolysis of fused alumina because the oxygen gas formed at the anode oxidizes the carbon of the anode to carbon dioxide.
(v) Extraction of aluminium was very difficult in the beginning because it was very expensive.
(vi) Carbon anodes are used in the electrolytic extraction of aluminium because carbon in the form of graphite is a good conductor of electricity.
(vii) Galvanized metal ions should not be used for storing food as food acids may react with the zinc coating and cause food poisoning.
3. Define the terms:
(i) Mineral
(ii) Ore
(iii) Gangue
(iv) Charge
(v) Flux
(vi) Slag
Answer
(i) Mineral: The naturally occurring compounds of metals which are generally mixed with earthy such as soil, sand, limestone and rocks are known as minerals.
(ii) Ore: Those minerals from which a metal can be extracted profitably are called ores.
(iii) Gangue: The rocky impurities like (SiO2) present in an ore are called gangue.
(iv) Charge: The mixture of materials fed into a furnace to extract a metal is called charge.
(v) Flux: The substance added to get rid of gangue in the extraction of metal is called flux.
(vi) Slag: The product obtained by the combination of gangue with flux is called slag.
4. (i) What is meant by concentration of ores?
(ii) Name the process of concentration,
(a) Based on densities
(b) Based on magnetic nature.
(iii) How an ore is concentrated by froth floatation process?
Answer
(i) The set of processes used to remove as much of gangue as possible, is known as concentration of ores. It is also known as ore dressing.
(ii) The process of concentration
- Based on densities is Gravity separation.
- Based on magnetic nature is Electromagnetic separation.
Figure: Froth floatation process
5. Name one metal each occurring as a
(a) Sulphide ore
(b) Halide ore
(c) Carbonate ore
(d) Oxide ore
Answer
(a) Mercury.
(b) Silver.
(c) Zinc.
(d) Aluminium.
6. Comment on the statement that- "All ores are minerals but all minerals are not ores".
Answer
As we know that minerals are the naturally occurring compounds of metals which are generally mixed with earthy such as soil, sand, limestone and rocks while ores are those minerals from which a metal can be extracted profitably.
Hence "All ores are minerals but all minerals are not ores".
7. Write the name and formulae of two ores for each of the following:
(a) Iron
(b) Zinc
(c) Aluminium
Answer
(a) Iron: Haematite (Fe2O3) and Magnetite (Fe3O4).
(b) Zinc: Zinc blende (ZnS) and Calamine (ZnCO3).
(c) Aluminium: Bauxite (Al2O3) and Cryolite (AlF3.3NaF).
8. Compare the process of calcination and roasting.
Answer
Comparison of calcination and roasting :
|
Calcination |
Roasting |
|
|
9. What is meant by refining of metals? Name the three common methods used for refining.
Answer
Refining of metals: It is the further purification of metals obtained by reduction process to remove all the impurities.
Depending upon the nature of metal, nature of impurities and purpose for which metal is to be used. The three methods used for refining are:
- Liquation.
- Distillation.
- Electrolytic refining.
10. How are metals refined by the electrolytic methods?
Answer
Electrolytic method: This method is based upon the phenomenon of electrolysis and is widely used to refine a number of metals such as copper, silver, gold etc. In this method, impure metal is made anode whereas a thin sheet of pure metal is used as cathode in an electrolytic tank. The electrolyte used in the tank is usually the acidified aqueous solution of a salt or complex salt of metal. On passing the electric current through electrodes the metal ions from anode go into the electrolyte solution. These cations gain electrons from the cathode and get deposited on it. The impurities either remain dissolved or get precipitated as anode mud.
At anode : M ⟶ Mn+ + ne−
At cathode : Mn+ + ne− → M where M is the metal to be refined.
11. (a) Name the ore from which aluminium is extracted.
(b) How is ore purified (give equations also)
(c) How is aluminium obtained from pure ore?
(d) Which method of refining is used to get 99.8% pure aluminium?
Answer
(a) Bauxite.
(b) Purification of aluminium ore is done by the Baeyer's process.
Baeyer's process involves the following steps :
- 1. Bauxite is crushed to a fine powder.
- 2. The powdered bauxite is then treated with a strong solution of sodium hydroxide.
- 3. The mixture is then heated under pressure to 150°C to 250°C, for about 30 minutes. The heat and the pressure cause the alumina to issolve in the sodium hydroxide to form sodium aluminate.
- Al2O3 . 2H2O + 2NaOH → 2NaAlO2 + 3H2O
- Alumina being amphoteric dissolves in sodium hydroxide.
- 4. The sodium aluminate solution is then filtered to separate the impurities.
- 5. The solution of sodium aluminate is then cooled lightly and sent into tanks called precipitators.
- 6. Crystals of aluminium hydroxide are then added when most of the sodium aluminate undergoes hydrolysis to precipitate insoluble aluminium hydroxide.
- NaAlO2 + 2H2O → NaOH + Al(OH)3
- 7. The solid aluminium hydroxide is separated by filtration.
- 8. The solid aluminium hydroxide is then washed and again filtered and dried, and then heated to about 1100°C to 1200°C, when aluminium hydroxide decomposes to form aluminium oxide.
2Al(OH)3 → Al2O3 + 3H2O
(i) Electrolyte used :
- Pure alumina
- Cryolite
- Aluminium fluoride
- Calcium fluoride or Fluorspar
- Cathode : inner lining of carbon
- Anode : Thick carbon rods dipping into the fused electrolytes.
(iii) Temperature of the electrolytic bath: 950°C
Reactions : On passage of electricity through electrolyte aluminium and oxide ions are formed.
At cathode : Aluminium ions get reduced as : 
Figure : Extraction of aluminium from pure ore
(d) Electrolytic refining.
12. In the Hall's process for extraction of aluminium,
(a) Give the formula and purpose of fluorspar and cryolite
(b) Sate the location of cathode and anode and explain what occurs at each electrode.
Answer
(a) Fluorspar is CaF2 and it helps in the mobility of the fused mixture.
(b) Cathode is the inner lining of gas - carbon of the electrolytic cell and anode is the thick carbon rods dipping into the fused electrolytes.
At cathode: Aluminium ions get reduced as : 
13. What is the role of cryolite (NaAlF6) in the electrolytic reduction of alumina in the Hall's process?
Answer
Cryolite acts as a solvent for the electrolytic mixture in the electrolytic reduction of alumina in the Hall's process.
14. (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.
(c) Why is food containing iron salts should not be cooked in aluminium utensils?
Answer
(a) Aluminium is a more active metal than iron, but suffers less corrosion because of t he formation of a thin, transparent, protective, non- porous adhering film of aluminium oxide on the surface of aluminium which makes it resistant to corrosion.
(b) Aluminium vessels should not be cleaned with powders containing alkalis because alunimun reacts with alkalis to form respective aluminate and hydrogen as :
2Al + 2NaOH + 2H2O → 2NaAlO2 + 3H2
(c) Food containing iron salts should not be cooked in aluminium utensils as there is a danger of aluminium toxicity.
15. Give equations for the following conversions:
(i) Ferric oxide to iron.
(ii) Aluminium hydroxide to aluminium oxide.
(iii) Aluminium to aluminium nitride.
(iv) Aluminium to sodium aluminate.
Answer
16. What is an alloy? Give three reasons why alloys are made.
Answer
An alloy is a homogeneous mixture of two or more metals fused together and then solidified.
Alloys are made because they have many salient features:
Tensile strength.
Strength.
Electrical hardness.
17. Give two properties of alloys which are different from constituent metals.
Answer
The properties of alloys which are different from constituent metals are:
- Alloys are stronger and harder than the metals of which they are made.
- Alloys are more resistant to corrosion.
18. What is an amalgam? Name one metal which does not form amalgam? State one use of amalgam.
Answer
Amalgam: A mixture or an alloy of mercury with a number of metals or non-metals is known as amalgams. An amalgam may be liquid such as Na/Hg or a solid like Zn/Hg.
Iron does not form amalgam.
Dental amalgam which is a mixture of mercury with a silver tin alloy is used for dental fillings.
19. Give composition and uses of each of the following alloys. Mention the reason for its use.
(i) Stainless steel
(ii) Duralumin
(iii) Brass
(iv) Magnalium
(v) Solder
(vi) Bronze
Answer
20. Explain the following:
(i) Galvanization protects iron from rusting
(ii) Stainless steel is more useful than steel.
(iii) Aluminium is extensively used for making aircraft parts.
(iv) Cold water has no action on aluminium.
Answer
(i) Galvanization protects iron from rusting because in galvanization coating of zinc is done over iron articles and zinc being more electropositive would be attacked preferably than iron.
(ii) Stainless steel is more useful than steel as it is harder, has high tensile strength, more lustre, more resistance to corrosion and many chemicals.
(iii) Aluminium is extensively used for making aircraft parts because of features like high tensile strength, corrosion resistance light but hard and tough.
(iv) Cold water has no action on aluminium while burning aluminium decomposes steam.
21. Complete and balance the following equations :
(i) Al + O2 →
(ii) Al + N2 →
(iii) Al + KOH + H2O →
(iv) Fe2O3 + → Al2O3 +
(v) Fe2O3 + CO →
Answer
22. Name oxide of one metal which is reduced by (give equation):
(i) Reduction with carbon
(ii) Electrolytic reduction
(iii) Reduction with heat alone
Answer
23. (i) An aqueous solution of sodium chloride is not used for electrolytic reduction of sodium metal. Why?
(ii) For the reaction of a metal oxide. Suggest a reducing agent other than carbon
Answer
(i) An aqueous solution of sodium chloride is not used for electrolytic reduction of sodium metal because if we electrolyse an aqueous solution of sodium chloride, then as soon as sodium metal is produced at the cathode, it will react with water to form sodium hydroxide. So electrolysis of aqueous sodium chloride solution will produce sodium hydroxide and not sodium metal.
(ii) Reducing agents for the reaction of a metal oxide: Aluminium, carbon monoxide and hydrogen.
24. What is (a) galvanized iron, and (b) passive iron?
Answer
(a) Iron having a coating of zinc is called galvanized iron.
(b) iron which cannot be easily acted upon by acids is called as passive iron. Galvanized iron is called passive iron since coating of zinc protects the iron from corrosion as zinc is more electropositive and so would be attacked first.
25. Name the alloy of zinc used in simple voltaic cells.
Answer
Zinc amalgam which is a mixture of zinc and mercury.
26. Complete and balance the following equation :
Al + NaOH ⟶
Answer
27. (a). Give the chemical name and formula of 'cryolite'
(b). what is the function of cryolite in the extraction of aluminium, other than acting as a solvent for bauxite?
Answer
(a). Cryolite is Na3AlF6 and its chemical name is Sodium aluminium fluoride.
(b). Cryolite is used in the electrolysis of alumina. The function of cryolite is to
(i) Reduce melting point of alumina
(ii) Make molten alumina a good conductor of electricity
28. Name a non-metallic element which
(a) forms acidic and neutral oxides
(b) Has a metallic lustre
(c) Is a liquid at ordinary temperatures
(d) Is a conductor of electricity
Answer
(a) Nitrogen.
(b)Iodine
(c) Bromine
(d) Carbon in the form of graphite
29. Name a metal which occurs free in nature.
Answer
Gold
30. Give the name and formula of an ore of zinc.
(a) Roasting of the ore
(b) Reduction of the zinc compound which is the product of above reaction.
(c) What in addition to a zinc compound, is put into the furnace? State one large scale use of zinc.
Answer
An ore of zinc is Zinc blende (ZnS). 
(c) In addition to zinc oxide carbon is put in the furnace to reduce it to zinc metal, large scale use of zinc is that it is used for electroplating
31. Arrange the metals: calcium, iron, magnesium and sodium in order of their reactivity with water placing the most reactive first.
Answer
Reactivity of metals with water Sodium, calcium, magnesium, iron
32. Write equations for each of the above metal which reacts with water.
Answer
33. The following questions refer to the extraction of aluminium and iron from their ores:
(a) Name the principle ore from which i. iron, and ii. Aluminium is extracted.
(b) What is the most important chemical process in the extraction of any metal? State how this essential step is carried out in the extraction of: i. iron, and ii. Aluminium.
(c) Iron and aluminum ores both, contain impurities. Explain briefly how these impurities are removed in each case.
(d) What is the major impurity present in iron when it is removed from the furnace?
Answer
(a) Ore of iron is haematite and ore of aluminum is bauxite.
(b) Reduction of the oxide is the most important chemical process in the extraction of any metal. 
34. Name an alloy of zinc which is used in simple voltaic cells.
Answer
Zinc amalgam.
35. For each of the substances listed below, explain its role in the extraction of aluminium:
(a) Bauxite
(b) Sodium hydroxide
(c) Cryolite
(d) Graphite
Answer
(a) Bauxite : It is the principle ore from which aluminium is extracted.
(b) Sodium hydroxide : It reacts with alumina to form sodium aluminate which is then further filtered to separate impurities. 
(c) Cryolite is used in the electrolysis of alumina. The function of cryolite is to
(1) Reduce melting point of alumina
(2) Make molten alumina a good conductor of electricity
(d) Graphite : It acts as electrodes in the electrolytic extraction of aluminium.
36. The following questions relate to the extraction of aluminium by electrolysis.
(a) Give the equation for the reaction which takes place at the cathode.
(b) Explain why it is necessary to renew the anode periodically.
Answer
37. What is an alloy? An alloy usually has some property which makes it useful in a specific way. What is the special property of:
(a) Duralumin (b) type metal?
Answer
An alloy is a homogeneous mixture of two or more metals fused together and then solidified.
(a) The special property of duralumin is:
- Light but hard
- Resistant to corrosion
- Ductile
38. What is added to steel to make it stainless steel?
Answer
Chromium and nickel is added to steel to make it stainless steel.
39. Define and explain the meaning of the term ore.
Answer
Ore Those minerals from which a metal can be extracted profitably are called ores. For example bauxite ore is used to extract aluminium metal, hematite ore is used to extract iron metal.
40. Complete the incomplete statements with missing words:
(a) Metals are ______ while non-metals are ______ conductors of heat.
(b) Metals are malleable while non-metals are ______.
(c) Metals form positive ions while non- metals ______.
(d) Non-metals form acidic oxides while metals form ______.
Answer
(a) good, poor.
(b) non-malleable.
(c) form negative ions.
(d) basic oxides.
41. Name:
(a) The metal which is liquid at room temperature.
(b) The allotrope of the non-metal carbon which conducts electricity.
Answer
(a) Mercury
(b) Graphite
42. How many valence electrons are present in (a) metals and (b) non- metals?
Answer
Metals have 1, 2, 3 valence electrons while non-metals have 4, 5, 6 or 7 valence electrons.
43. With reference to the reduction of copper (II) oxide , iron (II) oxide, lead (II) oxide and magnesium oxide; place the oxides in order of increasing ease of reduction.[i.e. first write the oxide that is most difficult to reduce and at last, the oxide, that is most easily reduced.]
Answer
Magnesium oxide, iron (II) oxide, lead (II) oxide and then copper (II) oxide.
44. Write balanced equations for the following reactions:
(a) Reduction of copper oxide by hydrogen.
(b) Reduction of iron (III) oxide by carbon monoxide.
(c) Reduction of lead (II) oxide by carbon.
Answer
45. (a) What is the type of bonding expected in a metallic chloride?
(b) If fused metallic chloride is electrolyzed, at which electrode would the metal be obtained?
(c) What metallic property is shown by the non-metal graphite?
Answer
(a) Ionic bonding is expected in a metallic chloride.
(b) Metal would be obtained at cathode.
(c) Graphite, like metals is a good conductor of electricity.
46. X is an element in the form of a powder. X burns in oxygen and the product is soluble in water. The solution is tested with litmus. Write down only the word which will correctly complete each of the following sentences:
(a) If X is a metal, then the litmus will turn ______.
(b) If X is a non-metal, then the litmus will turn ______.
(c) If X is a reactive metal, then ______ will be evolved, when X reacts with dilute sulphuric acid.
(d) If X is a non -metal, it will form _ oxide, which will form ______ solution with water.
(e) If X is a non -metal, it will not conduct electricity unless it is carbon in the form of ______.
Answer
(a) Blue
(b) Red
(c) Hydrogen
(d) acidic, acidic
(e) graphite.
47. 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 acid and alkalis.
(d) Does not react with cold water, but reacts with steam when heated.
Answer
(a) Copper
(b) Iron
(c) Zinc
(d) Magnesium
48. Arrange the metals of question (1) in the decreasing order of reactivity.
Answer
Sodium > magnesium > Zinc > Iron > Copper
49. List 1 contains the metals/alloys (1, 2, 3, 4, 5) and list 2 contains their uses (A, B, C, D,E).
|
List 1 |
List 2 |
|
1. Aluminium |
A. steel making |
Copy and complete the following table, write down the correct letter against the numbers representing metals. An answer may be used only once.
The first has been done for you.
|
Metal |
1 |
2 |
3 |
4 |
5 |
|
Use |
B |
|
|
|
|
Answer
|
Metal |
1 |
2 |
3 |
4 |
5 |
|
Use |
B |
D |
E |
A |
C |
50. In order to obtain one tone of aluminium, the following inputs are required:
4 tones 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 (II) 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 purification of bauxite.
(ii) Write the equation to show the action of heat on aluminium hydroxide.
(c) (i) Write the formula of cryolite.
(ii) Write down the word which correctly completes the following sentence;
"By dissolving aluminium oxide in cryolite, a ______ (conducting / non- conducting) solution is produced.
(iii) Why so much graphite required for this electrolytic process/
(iv) Write the equation for the reaction which takes place at cathode.
(d) In construction work, why is the alloy of aluminium, duralumin used rather than pure aluminium.
Answer
51. Compare the properties of a typical metal and a non- metal on the basis of the following:
(a) electronic configuration
(b) nature of oxides
(c) oxidizing or reducing action
(d) conductivity of heat and electricity
Answer
52. Name a non- metal that has a metallic luster and sublimes on heating.
Answer
Iodine is a non- metal that has a metallic luster and sublimes on heating.
53. Write balanced equation for the following reactions:
Aluminium powder is warmed with hot and concentrated caustic soda solution.
Answer
54. Name the ore of zinc containing its sulphide.
Answer
Zinc blende (ZnS)
55. Write the equations for the reaction of zinc with each of the following:
(a) Sodium hydroxide solution
(b) Dilute sulphuric acid
(c) Copper sulphate solution
Answer
56. To protect iron from rusting, it is coated with a thin layer of zinc. Name the process.
Answer
Galvanization.
57. 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 equations for the purification of bauxite by Hall's process.
(b) Name a chemicals used for dissolving aluminium oxide. In which state of sub-division 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. Which particular property of cast iron makes it unsuitable for the construction of bridges?
Answer
(b) Fluorspar and cryolite act as solvent. The percentage by weight composition is as follows :
Alumina - 20% by mass
Cryolite - 60% by mass
Fluorspar - 20% by mass
(d) As a reducing agent: Aluminium has a high affinity for oxygen. It readily removes oxygen from oxides of less reactive metals.
58. 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
(a) Write down the three letters each from the above list which are relevant to:
(i) Zinc
(ii) Aluminium
(b) Fill in the blanks using the most appropriate words from A to F:
(i) The ore from which aluminium is extracted must be treated with ______ so that pure aluminium oxide can be obtained.
(ii) Pure aluminium oxide is dissolved in ______ to make a conducting solution.
(c) Write the formula of cryolite.
Answer
(a) (i) B, D F
(ii) A, C E
(b) (i) Sodium hydroxide solution
(ii) Cryolite
(C) Na3AlF6
59. Calcium, copper, lead, aluminium, zinc, chromium, magnesium, iron.
Choose the major metals from the list given above to make the following alloys:
(a) Stainless steel
(b) brass
Answer
(a) For stainless steel: iron, chromium
(b) For brass: Copper and zinc.
60. Name the following:
(a) A metal which is liquid at room temperature.
(b) A compound which is added to lower the fusion temperature of the electrolytic bath in the extraction of aluminium.
(c) The process of heating an ore to a high temperature in the presence of air.
(d) The compound formed by the reaction between calcium oxide and silica.
(e) The middle region of the blast furnace.
Answer
(a) Mercury.
(b) Cryolite.
(c) Roasting.
(d) Calcium silicate.
(e) Zone of heat absorption.
61. The following is an extract from 'Metals in the service of Man, Alexander and street /Pelican 1976':
'Alumina has a very high melting point of over 2000oC 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'.
(a) Which solution is used to react with bauxite as a first step in obtaining pure aluminium oxide?
(b) The aluminium oxide for the electrolytic extraction of aluminium is obtained by heating aluminium hydroxide. Write the balanced chemical equation for this reaction.
(c) Name the element which serves both as the anode and the cathode in the extraction of aluminium.
(d) Write the balanced chemical equation for the reaction that occurs at the cathode during the extraction of aluminium by electrolysis.
(e) Give the balanced chemical equation fro the reaction which occurs at the anode when aluminium is purified by electrolysis.
Answer
(a) Sulphur, Phosphorous, Carbon, Iodine
(b) Copper, Lead, Zinc, Mercury
Answer
(a) Carbon as it forms very large number of compounds while the rest do not.
(b) Mercury as it is a liquid metal while the rest aresolid.
63. Correct the following statements:
(a) Copper reacts with nitric acid to produce nitrogen dioxide.
(b) Haematite is the chief ore of aluminium.
Answer
(a) Copper reacts with concentrated nitric acid to produce nitrogen dioxide.
(b) Bauxite is the chief ore of aluminium.
64. The sketch below illustrates the refining of aluminium by Hoope's process 
(a) Which of A and B is the cathode and which one is the anode ?
(b) What is the electrolyte in the tank ?
(c) what material is used for the cathode ?
Answer
(a) A is cathode and B is anode.
(b) Molten fluorides of Al, Na and Ba.
(c) Graphite rods.
65. State the property of the metal being utilized in the following:
|
Use of Metal |
Property |
|
Zinc in Galvanization |
|
|
Aluminium in Thermite welding |
|
Answer
|
Use of Metal |
Property |
|
Zinc in Galvanization |
Not affected by air and moisture |
|
Aluminium in Thermite welding |
Strong affinity for oxygen as compared to iron. |
66. Choose the correct answer:
Brass is an alloy of
(a) Copper and tin
(b) Copper and zinc
(c) Zinc and lead
(d) Lead and tin
Answer
(b) Copper and zinc(a) Metals are good conductors of electricity.
(b) Metals are malleable and ductile
(c) Metals form non-polar covalent compounds
(d) Metal will have 1 or 2 or 3 electrons in their valence shell.
Answer
(a) True
(b) True
(c) False.
Metals form ionic compounds.
(d) True
68. Name the main constituent metal in the following alloys:
(i) Duralumin
(ii) Brass
(iii) Stainless steel
Answer
(i) Duralumin
Al (95%)
Cu (4%)
Mg (0.5%)
Mn (0.5%)
(ii) Brass
Cu (60-70%)
Zn (30-40%)
(iii) Stainless steel
Fe (73%)
Cr (18%)
Ni (8%)
C (1%)
69. Choose the correct answer from the options given below: The metal is a liquid at room temperature.
(a) Potassium
(b) Zinc
(c) Gold
(d) Mercury
Answer
(d) Mercury
70. Answer the following questions :
(i) Name a metal which is found abundantly in earth's crust.
(ii) What is the difference between calcination and roasting.
(iii) Name the process used for the enrichment of sulphide ore.
(iv) Write the chemical formulae of main ore iron and aluminum.
(v) Write the constituents of electrolyte for the extraction of aluminum.
Answer
(i) A metal which is found abundantly in the Earth's crust is aluminium.
(ii) Differences between calcination and roasting:
|
Calcination |
Roasting |
|
1. The ore is heated in the absence of air. |
1. The ore is heated in excess of air. |
|
2. Moisture and organic impurities are removed, and the ore becomes porous and more reactive. |
2. Volatile impurities are removed as oxides (SO2, P2O5, As2O3), and the ore becomes porous and more reactive. |
|
3. Carbonate and hydrated ores are calcined, and CO2 or water vapour is given off. |
3. Sulphide ores are roasted, so SO2 is given off. |
(iii) Froth flotation process is used for the enrichment of sulphide ore.
(iv) Ore of iron
|
Name |
Chemical name |
Formula |
|
Red haematite |
Anhydrous ferric oxide |
Fe2O3 |
|
Brown haematite |
Hydrated ferric oxide |
2Fe2O3.3H2O |
Ores of aluminium
|
Name |
Chemical name |
Formula |
|
Bauxite |
Hydrated aluminium oxide |
Al3O32H2O |
|
Cryolite |
Sodium aluminium oxide |
Na3AlF6 |
(v) Constituents of the electrolyte for the extraction of aluminium are pure alumina (Al2O3) cryolite (Na3AlF6) and fluorspar (CaF₂).
71.
|
X |
Y |
|
|
Normal Electronic Configuration |
2,8,7 |
2,8,2 |
|
Nature of Oxide |
Dissolves in water and truns blue litmus red. |
Very low solublity in water. Dissolves in hydrochloric acid. |
|
Tendency for Oxidising and reducing reactions |
Tends to oxidise elements and compound |
Tends to act as a reducing agent |
|
Electrical and Thermal Conductivity |
Very poor electrical conductor Poor thermal conductivity |
Good electrical conductor Good thermal conductor |
|
Tendency to form Alloys and Amalgams |
No tendency to form alloys |
Forms alloys |
Using the information above, complete the following :
(i) _________ is the metallic element.
(ii) Metal atoms tend to have a maximum of ________ electrons in the outermost energy level.
(iii) Non-metallic elements tend to form _________ oxides while metals tend to form _______oxides.
(iv) Non-metallic elements tend to be ______ conductors of heat and electricity.
(v) Metals tend to _______ electrons and act as ________ agents in their reactions with elements and compounds.
Answer
(i) Y is the metallic element.
(ii) Metal atoms tend to have a maximum of 3 electrons in the outermost energy level.
(iii) Non-metallic elements tend to form acidic oxides, while metals tend to form basic oxides.
(iv) Non-metallic elements tend to be poor conductors of heat and electricity.
(v) Metals tend to lose electrons and act as reducing agents in their reactions with elements and compounds.
72. The metals zinc and tin are present in the alloy
(i) Solder
(ii) Brass
(iii) Bronze
(iv) Duralumin
Answer
Bronze
73. The following questions relate to the extraction of aluminium by electrolysis.
(i) Name the other aluminium containing compound added to alumina and state the significance
(ii) Give the equation for the reaction that takes place at the cathode
(iii) Explain why is it necessary to renew the anode periodically
Answer
Extraction of aluminium:
(i) Cryolite (Na3AlF6) is added along with alumina and fluorspar. It lowers the fusion temperature from 2050°C to 950°C and enhances conductivity.
(ii) Al3+ + 3e-→ Al
(iii) It is necessary to renew the anode periodically as it gets oxidised by the oxygen evolved at the anode.
74. State the main components of the following alloys :
(i) Brass
(ii) Duralumin
(iii) Bronze
Answer
(i) Main components of brass are copper and zinc.
(ii) Main components of duralumin are aluminium, magnesium, copper and manganese.
(iii) Main components of bronze are copper, zinc and tin.
75. Name the following
(i) The property possessed by metals by which they can be beaten into sheets
(ii) A compound added to lower the fusion temperature of electrolytic bath in the extracton of aluminium
(iii) The ore of zinc containing its sulphide
Answer
(i) Malleability is the property possessed by metals by which they can be beaten into sheets.
(ii) Cryolite is added to lower the fusion temperature of an electrolytic bath in the extraction of aluminium.
(iii) Zinc blende (sphalerite) is the ore of zinc containing its sulphide.
76. The main ore used for the extraction of iron is
(a) Haematite
(b) Calamine
(c) Bauxite
(d) Cryolite
Answer
(a) The main ore used for the extraction of iron is haematite.
77. Heating an ore in a limited supply of air or in the absence of air at a temperature just below its melting point is known as
(a) Smelting
(b) Ore dressing
(c) Calcination
(d) bessemerisation
Answer
(c) Heating an ore in a limited supply of air or in the absence of air at a temperature just below its melting point is known as calcination.
78. Aluminium powder is used in thermite welding because
(a) It is a strong reducing agent
(b) It is a strong oxidizing agent
(c) It is corrosion resistant
(d) It is a good conductor of heat
Answer
(a) It is a strong reducing agent.
79. This is not an alloy of copper:
(a) Brass
(b) Bronze
(c) Solder
(d) Durlamium
Answer
(c) Solder
80. For each of the substance listed below, describe the role played in the extraction of aluminum
(a) Cryolite
(b) Sodium hydroxide
(c) Graphite
Answer
In the extraction of aluminium, the given compounds play the following roles:
(a) Cryolite: It lowers the fusion temperature from 2050°C to 950°C and enhances conductivity.
(b) Sodium hydroxide:
Two roles are played by sodium hydroxide in the extraction of aluminium.
First, finely grinded bauxite (ore of aluminium) is heated under pressure with conc. caustic soda solution (NaOH solution) for 2-8 hours at 140°C to 150°C to produce sodium aluminate. The chemical equation is as follows:
Al2O3.2H2O + 2NaOH → 2NaAlO2+ 3H2O
Second, on diluting sodium aluminate with water and cooling to 50°C, sodium aluminate is hydrolysed to give aluminium hydroxide as a precipitate. Here, the impurities dissolve in sodium hydroxide.
(c) Graphite: Thick rods of graphite are suspended in the fused electrolyte. They act as an anode where oxygen gas is discharged.
81. Explain why :
(i) In the electrolysis of alumina using the Hall Heroult's Process the electrolyte is covered with powdered coke.
(ii) Iron sheets are coated with zinc during galvanization.
Answer
(i) In the electrolysis of alumina using the Hall-Héroult process, the electrolyte is covered with powdered coke as it
- reduces heat loss by radiation
- prevents the burning of the anode
(ii) Iron sheets are coated with zinc during galvanisation to prevent them from rusting.
82. (i) Name the solution used to react with bauxite as a first step in obtaining pure aluminium oxide,in the Baeyer's process.
(ii) Write the equation for the reaction where the aluminium oxide for the electrolytic extraction of aluminium is obtained by heating aluminium hydroxide.
(iii) Name the compound added to pure alumina to lower the fusion temperature during the electrolytic reduction of alumina.
(iv) Write the equation for the reaction that occurs at the cathode during the extraction by aluminium by electrolysis.
(v) Explain why it is preferably to use a number of graphite electrodes as anode instead of a single electrode, during the above electrolysis.
Answer
(i) Conc. caustic soda
(iii) Cryolite
(iv) At the cathode: Al3++ 3e-→ Al
(v) The anode has to be replaced from time to time as it gets oxidised by oxygen evolved at the anode.
83. The two main metals in bronze are
(a) Copper and zinc
(b) Copper and lead
(c) Copper and nickel
(d) Copper and tin
Answer
Copper and tin
84. Name the following :
(i) The process of coating of iron with zinc
(ii) An alloy of lead and tin that is use in electrical circuits
(iii) An ore of zinc containing its sulphide
(iv) A metal oxide that can be reduced by hydrogen
Answer
(i) Electroplating
(ii) Solder
(iii) Zinc blende
(iv) PbO or CuO
85. Answer the following questions with respect by hydrogen
(i) Identify the components of the electrolyte other than pure alumina and the role played by each
(ii) Explain why powdered coke is sprinkled over than electrolytic mixture.
Answer
(i) Components of electrolyte: Cryolite and fluorspar
Role played by each electrolyte is given below:
- Cryolite lowers the fusion temperature from 2050°C to 950°C and enhances conductivity.
- Fluorspar andcryolite act as a solvent for the electrolytic mixture and increase conductivity.
(ii) Powdered coke is sprinkled over the surface of the electrolytic mixture for the following reasons:
- To reduce heat loss by radiation
- To prevent burning of the anode
86. Complete the following by selecting the correct option from the choices given
(i) The metal which does not react with water or dilute H2SO4 but reacts with concentrated H2SO4 is _________ (Al/Cu/Zn/Fe)
(ii) The metal whose oxide, which is amphoteric, is reduced to metal by carbon reduction ________ (Fe/Mg/Pb/Al)
(iii) The diavalent metal whose oxide is reduced to metal by electrolysis of its fused salt is ________ (Al/Na/Mg/K)
Answer
(i) Cu
(ii) Pb
(iii) Al
87. From the list of terms given, choose the most appropriate term to match the given description (Calcination, roasting, pulverization, smelting)
(i) Crushing of the ore into a fine powder
(ii) Heating of the ore in the absence of air to high temperature
Answer
(i) The process of crushing ores into a fine powder in big crushers and ball mills is known as pulverisation.
(ii) Heating of the ore in the absence of air to a high temperature that is high but insufficient to melt the ore is known as calcination.