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Page No 18:
Question 1:
Which of the following property is generally not shown by metals?
(a) Electrical conduction
(b) Sonorous in nature
(c) Dullness
(d) Ductility
Answer:
Out of all the given options, dullness is the only property which is not shown by any metal as the metals are lustrous in nature.
Hence, the correct answer is option (c).
Page No 18:
Question 2:
The ability of metals to be drawn into thin wire is known as
(a) ductility
(b) malleability
(c) sonorousity
(d) conductivity
Answer:
The ability of metals to be drawn into a thin wire is known as ductility.
Hence, the correct answer is option (a).
Page No 18:
Question 3:
Aluminium is used for making cooking utensils. Which of the following properties of aluminium are responsible for the same?
(i) Good thermal conductivity
(ii) Good electrical conductivity
(iii) Ductility
(iv) High melting point
(a) (i) and (ii)
(b) (i) and (iii)
(c) (ii) and (iii)
(d) (i) and (iv)
Answer:
Aluminium is used for making cooking utensils because it is a good conductor of heat and has a high melting point of about . So, when on top of a stove the aluminium vessel would not melt while cooking.
Hence, the correct answer is option (d).
Page No 18:
Question 4:
Which one of the following metals do not react with cold as well as hot water?
(a) Na
(b) Ca
(c) Mg
(d) Fe
Answer:
Out of the given options, only iron is the metal that does not react with cold as well as hot water.
Hence, the correct answer is option (d).
Page No 19:
Question 5:
Which of the following oxide(s) of iron would be obtained on prolonged reaction of iron with steam?
(a) FeO
(b) Fe2O3
(c) Fe3O4
(d) Fe2O3 and Fe3O4
Answer:
Iron does not react with cold or hot water, but steam is passed over a red hot iron, it reacts to form iron (II, III) oxide and hydrogen gas.
Hence, the correct answer is option (c).
Page No 19:
Question 6:
What happens when calcium is treated with water?
(i) It does not react with water
(ii) It reacts violently with water
(iii) It reacts less violently with water
(iv) Bubbles of hydrogen gas formed stick to the surface of calcium
(a) (i) and (iv)
(b) (ii) and (iii)
(c) (i) and (ii)
(d) (iii) and (iv)
Answer:
Calcium reacts slowly with water. If a piece of calcium is dropped into a non-reactive container containing water after some times bubbles of hydrogen gas are seen stuck to the surface of the metal.
Hence, the correct answer is option (d).
Page No 19:
Question 7:
Generally metals react with acids to give salt and hydrogen gas. Which of the following acids does not give hydrogen gas on reacting with metals (except Mn and Mg)?
(a) H2SO4
(b) HCl
(c) HNO3
(d) All of these
Answer:
Out of the given options, only nitric acid when reacting with metals does not give hydrogen gas instead nitric acid is a very strong oxidising agent and it oxidises the hydrogen gas formed to water and thus hydrogen gas is not evolved.
Hence, the correct answer is option (c).
Page No 19:
Question 8:
The composition of aqua-regia is
| (a) | Dil.HCl | : | Conc. HNO3 |
| 3 | : | 1 | |
| (b) | Conc. HCl | : | Dil. HNO3 |
| 3 | : | 1 | |
| (c) | Conc. HCl | : | Conc. HNO3 |
| 3 | : | 1 | |
| (d) | Dil.HCl | : | Dil. HNO3 |
| 3 | : | 1 |
Answer:
Aqua-regia is a mixture of concentrated hydrochloric acid and nitric acid in a molar ratio of 3 : 1.
Hence, the correct answer is option (c).
Page No 19:
Question 9:
Which of the following are not ionic compounds?
(i) KCl
(ii) HCl
(iii) CCl4
(iv) NaCl
(a) (i) and (ii)
(b) (ii) and (iii)
(c) (iii) and (iv)
(d) (i) and (iii)
Answer:
Out of the given options, HCl and CCl4 are the chemical compounds which have covalent bonding within its atoms.
Hence, the correct answer is option (b).
Page No 20:
Question 10:
Which one of the following properties is not generally exhibited by ionic compounds?
(a) Solubility in water
(b) Electrical conductivity in solid state
(c) High melting and boiling points
(d) Electrical conductivity in molten state
Answer:
There are no free moving ions in an ionic compound in its solid-state so, ionic compounds in their solid-state does not conduct electricity.
Hence, the correct answer is option (b).
Page No 20:
Question 11:
Which of the following metals exist in their native state in nature?
(i) Cu
(ii) Au
(iii) Zn
(iv) Ag
(a) (i) and (ii)
(b) (ii) and (iii)
(c) (ii) and (iv)
(d) (iii) and (iv)
Answer:
Silver and gold are noble metals and in nature, they exist in their free state and not in any combined state as ore.
Hence, the correct answer is option (c).
Page No 20:
Question 12:
Metals are refined by using different methods. Which of the following metals are refined by electrolytic refining?
(i) Au
(ii) Cu
(iii) Na
(iv) K
(a) (i) and (ii)
(b) (i) and (iii)
(c) (ii) and (iii)
(d) (iii) and (iv)
Answer:
Among the given metals, sodium (Na) and potassium (K) are highly reactive metals and are extracted by the electrolytic reduction of their molten chloride salts. Copper (Cu) and gold (Au) are extracted by electrolytic refining.
Hence, the correct answer is option (a).
Page No 20:
Question 13:
Silver articles become black on prolonged exposure to air. This is due to the formation of
(a) Ag3N
(b) Ag2O
(c) Ag2S
(d) Ag2S and Ag3N
Answer:
Silver objects corrode slowly in the air due to the presence of hydrogen sulphide which reacts with silver articles to form a black coloured chemical compound silver sulphide.
Hence, the correct answer is option (c).
Page No 20:
Question 14:
Galvanisation is a method of protecting iron from rusting by coating with a thin layer of
(a) Gallium
(b) Aluminium
(c) Zinc
(d) Silver
Answer:
Galvanisation is a method for the protection of iron articles from rusting. In this method, a thin coating of a more reactive metal like zinc is coated on top of the iron article to be protected.
Hence, the correct answer is option (c).
Page No 20:
Question 15:
Stainless steel is very useful material for our life. In stainless steel, iron is mixed with
(a) Ni and Cr
(b) Cu and Cr
(c) Ni and Cu
(d) Cu and Au
Answer:
Stainless steel is an alloy of iron made by mixing different metals like about 11% of chromium, nickel, molybdenum and niobium etc. and carbon with a maximum concentration of about 1.2%.
Hence, the correct answer is option (a).
Page No 21:
Question 16:
If copper is kept open in air, it slowly loses its shining brown surface and gains a green coating. It is due to the formation of
(a) CuSO4
(b) CuCO3
(c) Cu(NO3)2
(d) CuO
Answer:
Copper metal kept open in the air, slowly undergoes the process of corrosion to form a characteristic blue-green coating on top of the metal surface. The corrosion of copper metal in air occurs in several steps:
Hence, the correct answer is option (b).
Page No 21:
Question 17:
Generally, metals are solid in nature. Which one of the following metals is found in liquid state at room temperature?
(a) Na
(b) Fe
(c) Cr
(d) Hg
Answer:
Mercury is a metal which has a melting point of . So, at room temperature, it exists in the liquid state.
Hence, the correct answer is option (d).
Page No 21:
Question 18:
Which of the following metals are obtained by electrolysis of their chlorides in molten state ?
(i) Na
(ii) Ca
(iii) Fe
(iv) Cu
(a) (i) and (iv)
(b) (iii) and (iv)
(c) (i) and (iii)
(d) (i) and (ii)
Answer:
Sodium and calcium are the metals obtained from their chloride ores by electrolysis in the molten state.
Hence, the correct answer is option (d).
Page No 21:
Question 19:
Generally, non-metals are not lustrous. Which of the following nonmetal is lustrous?
(a) Sulphur
(b) Oxygen
(c) Nitrogen
(d) Iodine
Answer:
Iodine in nature exists in its molecular crystalline form and due to this iodine has a lustrous nature.
Hence, the correct answer is option (d).
Page No 21:
Question 20:
Which one of the following four metals would be displaced from the solution of its salts by other three metals?
(a) Mg
(b) Ag
(c) Zn
(d) Cu
Answer:
Out of the given options, silver metal is the least reactive metal and so, it can be displaced by the other metals form its salt.
Hence, the correct answer is option (b).
Page No 21:
Question 21:
2 mL each of concentrated HCl, HNO3 and a mixture of concentrated HCl and concentrated HNO3 in the ratio of 3 : 1 were taken in test tubes labelled as A, B and C. A small piece of metal was put in each test tube. No change occurred in test tubes A and B but the metal got dissolved in test tube C respectively. The metal could be
(a) Al
(b) Au
(c) Cu
(d) Pt
Answer:
A mixture of concentrated and concentrated in the 3 : 1 molar ratio is called aqua regia. It is a yellow-orange fuming liquid that can dissolve gold.
Hence, the correct answer is option (b).
Page No 22:
Question 22:
An alloy is
(a) an element
(b) a compound
(c) a homogeneous mixture
(d) a heterogeneous mixture
Answer:
An alloy is a homogeneous mixture of metals or metals combined with one or more other elements.
Hence, the correct answer is option (c)
Page No 22:
Question 23:
An electrolytic cell consists of
(i) positively charged cathode
(ii) negatively charged anode
(iii) positively charged anode
(iv) negatively charged cathode
(a) (i) and (ii)
(b) (iii) and (iv)
(c) (i) and (iii)
(d) (ii) ad (iv)
Answer:
In an electrolytic cell, the electrode that is connected to the positive end of a battery is called the anode and the electrode connected to the negative end of the battery is called the cathode.
Hence, the correct answer is option (b).
Page No 22:
Question 24:
During electrolytic refining of zinc, it gets
(a) deposited on cathode
(b) deposited on anode
(c) deposited on cathode as well as anode
(d) remains in the solution
Answer:
In the electrolytic refining process, the metal gets discharged at the cathode by reduction.
Hence, the correct answer is option (a).
Page No 22:
Question 25:
An element A is soft and can be cut with a knife. This is very reactive to air and cannot be kept open in air. It reacts vigorously with water. Identify the element from the following
(a) Mg
(b) Na
(c) P
(d) Ca
Answer:
Sodium is a third-period alkali metal which is a soft metal and highly reactive. sodium is stored under kerosene and whenever it comes in contact with air or water it reacts vigorously.
Hence, the correct answer is option (b).
Page No 22:
Question 26:
Alloys are homogeneous mixtures of a metal with a metal or nonmetal. Which among the following alloys contain non-metal as one of its constituents?
(a) Brass
(b) Bronze
(c) Amalgam
(d) Steel
Answer:
Steel is an alloy of iron with other metals like nickel, chromium, niobium and carbon.
Hence, the correct answer is option (d).
Page No 22:
Question 27:
Which among the following statements is incorrect for magnesium metal?
(a) It burns in oxygen with a dazzling white flame
(b) It reacts with cold water to form magnesium oxide and evolves hydrogen gas
(c) It reacts with hot water to form magnesium hydroxide and evolves hydrogen gas
(d) It reacts with steam to form magnesium hydroxide and evolves hydrogen gas
Answer:
Magnesium does not react with cold water. It only reacts with hot water or steam to form magnesium hydroxide and hydrogen gas.
Hence, the correct answer is option (b).
Page No 23:
Question 28:
Which among the following alloys contain mercury as one of its constituents?
(a) Stainless steel
(b) Alnico
(c) Solder
(d) Zinc amalgam
Answer:
Amalgam is an alloy of mercury with other metals like zinc, gold, silver or copper etc.
Hence, the correct answer is option (d).
Page No 23:
Question 29:
Reaction between X and Y, forms compound Z. X loses electron and Y gains electron. Which of the following properties is not shown by Z?
(a) Has high melting point
(b) Has low melting point
(c) Conducts electricity in molten state
(d) Occurs as solid
Answer:
A chemical compound formed by the gain and loss of electrons is called an ionic compound. Ionic compounds occur as solids, conduct electricity in the molten state and has a high melting point.
Hence, the correct answer is option (b).
Page No 23:
Question 30:
The electronic configurations of three elements X, Y and Z are X – 2, 8; Y – 2, 8, 7 and Z – 2, 8, 2. Which of the following is correct?
(a) X is a metal
(b) Y is a metal
(c) Z is a non-metal
(d) Y is a non-metal and Z is a metal
Answer:
Out of X, Y and Z, X and Y are non-metala and Z is a metal.
Hence, the correct answer is option (d).
Page No 23:
Question 31:
Although metals form basic oxides, which of the following metals form an amphoteric oxide?
(a) Na
(b) Ca
(c) Al
(d) Cu
Answer:
Out of all the given options, aluminium forms an amphoteric oxide , which can both act as an acid or a base.
Hence, the correct answer is option (c).
Page No 23:
Question 32:
Generally, non-metals are not conductors of electricity. Which of the following is a good conductor of electricity?
(a) Diamond
(b) Graphite
(c) Sulphur
(d) Fullerene
Answer:
Out of the given options, only graphite is a good conductor of electricity due to the presence of free electrons.
Hence, the correct answer is option (b).
Page No 23:
Question 33:
Electrical wires have a coating of an insulting material. The material, generally used is
(a) Sulphur
(b) Graphite
(c) PVC
(d) All can be used
Answer:
Polyvinyl chloride is a synthetic plastic polymer which is a bad conductor of electricity and thus used as an insulating coating material for metallic wires.
Hence, the correct answer is option (c).
Page No 24:
Question 34:
Which of the following non-metals is a liquid?
(a) Carbon
(b) Bromine
(c) Phosphorus
(d) Sulphur
Answer:
Out of the given options, only bromine exists a liquid non-metal under standard conditions.
Hence, the correct answer is option (b).
Page No 24:
Question 35:
Which of the following can undergo a chemical reaction?
(a) MgSO4 + Fe
(b) ZnSO4 + Fe
(c) MgSO4 + Pb
(d) CuSO4 + Fe
Answer:
Iron is more reactive than copper and thus, can replace copper from its salt.
Hence, the correct answer is option (d).
Page No 24:
Question 36:
Which one of the following figures correctly describes the process of electrolytic refining?
(a)
(b)
(c)
(d)
Answer:
In the process of electrolytic refining of copper, the impure copper metal is made the anode and connected to positive terminal of the battery. A thin strip of pure copper metal is made the cathode and connected to negative terminal of the battery. A solution of the metal salt (CuSO4) is used as an electrolyte. On passing the current through the electrolyte, the pure metal from the anode dissolves into the electrolyte as Cu2+. An equivalent amount of pure metal from the electrolyte is deposited on the cathode. The soluble impurities go into the solution, whereas, the insoluble impurities settle down at the bottom of the anode and are known as anode mud.
Hence, the correct answer is option (c).
Page No 24:
Question 37:
Iqbal treated a lustrous, divalent element M with sodium hydroxide. He observed the formation of bubbles in reaction mixture. He made the same observations when this element was treated with hydrochloric acid. Suggest how can he identify the produced gas. Write chemical equations for both the reactions.
Answer:
The lustrous divalent element M can be an amphoteric metal like Zn, Sn or Pb etc. When zinc is treated with sodium hydroxide it forms sodium zincate and hydrogen gas. When zinc is treated with hydrochloric acid it forms zinc chloride and hydrogen gas, and that is why Iqbal made the same observation.
To test the hydrogen gas produced in the chemical reaction, if a glowing splint in brought near the gas produced then it would burn with a pop sound.
Page No 24:
Question 38:
During extraction of metals, electolytic refining is used to obtain pure metals.
(a) Which material will be used as anode and cathode for refining of silver metal by this process?
(b) Suggest a suitable electrolyte also.
(c) In this electrolytic cell, where do we get pure silver after passing electric current?
Answer:
(a) During extraction of silver metal, impure metal will be used as anode and pure metal is used as a cathode for
refining of silver metal by this electrolytic refining.
(b) Silver Sulphate or Silver Nitrate could be used as an electrolyte.
(c) Pure silver is obtained on the cathode.
Page No 25:
Question 39:
Why should the metal sulphides and carbonates be converted to metal oxides in the process of extraction of metal from them?
Answer:
The extraction of metal becomes easier from its oxide than from its sulphide or the carbonate ore. That is why the metal sulphides and carbonates are converted to metal oxides in the process of extraction of metal from them.
Page No 25:
Question 40:
Generally, when metals are treated with mineral acids, hydrogen gas is liberated but when metals (except Mn and Mg), treated with HNO3, hydrogen is not liberated, why?
Answer:
Concentrated nitric acid is a very strong oxidising agent. When metals are treated with concentrated nitric acid the hydrogen gas that is produced during the reaction is further oxidised to water and thus hydrogen gas is not liberated.
Page No 25:
Question 41:
Compound X and aluminium are used to join railway tracks.
(a) Identify the compound X
(b) Name the reaction
(c) Write down its reaction.
Answer:
(a) Compound X is
(b) Displacement reaction.
(c)
Page No 25:
Question 42:
When a metal X is treated with cold water, it gives a basic salt Y with molecular formula XOH (Molecular mass = 40) and liberates a gas Z which easily catches fire. Identify X, Y and Z and also write the reaction involved.
Answer:
When sodium metal is treated with cold water, it gives a base sodium hydroxide and hydrogen gas is liberated which undergo explosive combustion reaction in an atmosphere of oxygen gas with a pop sound.
Hence, metal X is sodium, base Y is sodium hydroxide and gas Z is hydrogen gas.
Page No 25:
Question 43:
A non-metal X exists in two different forms Y and Z. Y is the hardest natural substance, whereas Z is a good conductor of electricity. Identify X, Y and Z.
Answer:
Carbon exist in two different forms of diamond and graphite. Diamond is the hardest natural substance, whereas graphite is a good conductor of electricity.
Hence, non-metal X is carbon, Y is diamond and Z is graphite.
Page No 25:
Question 44:
The following reaction takes place when aluminium powder is heated with MnO2
3 MnO2 (s) + 4 Al (s) → 3 Mn (l) + 2 Al2O3 (l) + Heat
(a) Is aluminium getting reduced?
(b) Is MnO2 getting oxidised?
Answer:
In the given chemical reaction, aluminium is acting as a reducing agent. Aluminium is helping in the reduction of manganese dioxide to manganese and itself getting oxidised to aluminium oxide.
(a) No, aluminium is getting oxidised.
(b) No, is getting reduced.
Page No 25:
Question 45:
What are the constituents of solder alloy? Which property of solder makes it suitable for welding electrical wires?
Answer:
The main constituents of solder alloy are tin and lead in a ratio of 60 : 40. Solder alloy has a low melting point of , this low melting point makes it suitable for soldering electrical wires.
Page No 25:
Question 46:
A metal A, which is used in thermite process, when heated with oxygen gives an oxide B, which is amphoteric in nature. Identify A and B. Write down the reactions of oxide B with HCl and NaOH.
Answer:
Aluminium metal is used in the thermite reaction. When aluminium is heated with oxygen it gives a chemical compound aluminium oxide. Aluminium oxide is amphoteric in nature thus, it acts both as acid and base.
Hence, metal A is aluminium and oxide B is aluminium oxide.
Page No 25:
Question 47:
A metal that exists as a liquid at room temperature is obtained by heating its sulphide in the presence of air. Identify the metal and its ore and give the reaction involved.
Answer:
Mercury is the metal which is liquid at room temperature. Ore of Mercury is Cinnabar. When we heat cinnabar in
atmospheric oxygen following reaction takes place.
Page No 25:
Question 48:
Give the formulae of the stable binary compounds that would be formed by the combination of following pairs of elements.
(a) Mg and N2
(b) Li and O2
(c) Al and Cl2
(d) K and O2
Answer:
(a) Magnesium Nitride (Mg3N2 )
(b) Lithium Oxide( Li2O)
(c) Aluminium Chloride( AlCl3 )
(d) Potassium Oxide ( K2O)
Page No 25:
Question 49:
What happens when
(a) ZnCO3 is heated in the absence of oxygen?
(b) a mixture of Cu2O and Cu2S is heated?
Answer:
(a) When is heated in the absence of oxygen, zinc oxide and carbon dioxide are liberated.
(b) When a mixture of and is heated we get the pure copper.
Page No 26:
Question 50:
A non-metal A is an important constituent of our food and forms two oxides B and C. Oxide B is toxic whereas C causes global warming
(a) Identify A, B and C
(b) To which Group of Periodic Table does A belong?
Answer:
(a) A is carbon, B is carbon monoxide and C is carbon dioxide.
(b) Carbon belongs to group number 14 in the modern periodic table.
Page No 26:
Question 51:
Give two examples each of the metals that are good conductors and poor conductors of heat respectively.
Answer:
Metals that are good conductor fo heat - iron and copper
Metals that are poor conductor of heat - lead and mercury
Page No 26:
Question 52:
Name one metal and one non-metal that exist in liquid state at room temperature. Also name two metals having melting point less than 310 K (37°C)
Answer:
Metal that exists in a liquid state at room temperature - mercury.
Non-metal that exists in a liquid state at room temperature - bromine
Two metals that have a melting point less than 310 K are:
Mercury - 234.32 K
Gallium - 302.91 K
Page No 26:
Question 53:
An element A reacts with water to form a compound B which is used in white washing. The compound B on heating forms an oxide C which on treatment with water gives back B. Identify A, B and C and give the reactions involved.
Answer:
A is calcium, B is calcium hydroxide and C is calcium oxide.
Page No 26:
Question 54:
An alkali metal A gives a compound B (molecular mass = 40) on reacting with water. The compound B gives a soluble compound C on treatment with aluminium oxide. Identify A, B and C and give the reaction involved.
Answer:
Alkali metal sodium when reacting with water gives a chemical compound sodium hydroxide. When sodium hydroxide is treated with aluminium oxide gives a soluble compound sodium aluminate.
Hence, A is sodium, B is sodium hydroxide and C is sodium aluminate.
Page No 26:
Question 55:
Give the reaction involved during extraction of zinc from its ore by
(a) roasting of zinc ore
(b) calcination of zinc ore
Answer:
Page No 26:
Question 56:
A metal M does not liberate hydrogen from acids but reacts with oxygen to give a black colour product. Identify M and black coloured product and also explain the reaction of M with oxygen.
Answer:
Copper is the metal which does not react with acids to liberate hydrogen gas. With oxygen, it forms Copper Oxide.
Hence, metal M is copper and the black coloured product is copper oxide.
Page No 26:
Question 57:
An element forms an oxide A2O3 which is acidic in nature. Identify A as a metal or non-metal.
Answer:
Element A is a non-metal because the oxides of non-metals are acidic in nature.
Page No 26:
Question 58:
A solution of CuSO4 was kept in an iron pot. After few days the iron pot was found to have a number of holes in it. Explain the reason in terms of reactivity. Write the equation of the reaction involved.
Answer:
According to the reactivity series of metals, iron is more reactive than copper and hence can displace copper from its salt. When a solution of copper sulphate is stored in the iron pot, a displacement reaction happened and iron from the pot came into the solution forming iron sulphate and thus the holes were formed in the pot.
Page No 26:
Question 59:
A non-metal A which is the largest constituent of air, when heated with H2 in 1:3 ratio in the presence of catalyst (Fe) gives a gas B. On heating with O2 it gives an oxide C. If this oxide is passed into water in the presence of air it gives an acid D which acts as a strong oxidising agent.
(a) Identify A, B, C and D
(b) To which group of periodic table does this non-metal belong?
Answer:
(a) Non-metal A is nitrogen because it is the largest constituent of air which constitute around 78% of the gases, B is
ammonia, C is Nitrogen dioxide and D is Nitric acid.
When heated with H2 in 1:3 ratio in the presence of a catalyst Fe, the following reaction takes place:
On heating nitrogen with O2, it gives nitrogen dioxide.
When nitrogen dioxide is passed into the water in the presence of air it gives nitric acid.
(b) Nitrogen belongs to group 15 of the modern periodic table.
Page No 27:
Question 60:
Give the steps involved in the extraction of metals of low and medium reactivity from their respective sulphide ores.
Answer:
In the extraction of metal from their sulphide ores, the ore is first kept for the process of roasting in which it is heated in the presence of air below its melting point to convert the sulphide ore to its oxide form.
For example, Cinnabar is heated in the air which mercuric sulphide gets oxidised to produce mercuric oxide.
Mercuric oxide is further reduced by heating to get pure mercury.
In the case of zinc which is a metal of medium reactivity and its ore is zinc blende.
Zinc blend is roasted to get zinc oxide.
When zinc oxide is reduced in the presence of coke, pure zinc metal is produced.
Page No 27:
Question 61:
Explain the following
(a) Reactivity of Al decreases if it is dipped in HNO3
(b) Carbon cannot reduce the oxides of Na or Mg
(c) NaCl is not a conductor of electricity in solid state whereas it does conduct electricity in aqueous solution as well as in molten state
(d) Iron articles are galvanised.
(e) Metals like Na, K, Ca and Mg are never found in their free state in nature.
Answer:
(a) Reactivity of aluminium decreases if it is dipped in nitric acid because it is a strong oxidizing agent. When aluminium is dipped into nitric acid a layer of aluminium oxide gets deposited on top of the aluminium article because of which reactivity of aluminium gets reduced.
(b) Oxides of sodium and magnesium are very strong oxides and carbon is not a very strong reducing agent hence, carbon cannot reduce the oxides of sodium and magnesium.
(c) In the solid-state, sodium chloride does not contain any free ions and thus is not able to conduct electricity. Whereas in the molten or aqueous state free moving ions of sodium chloride causes the conduction of electricity.
(d) Iron undergoes a slow but spontaneous process of corrosion which is known as rusting, in which the top layer of the article gets degraded over time. To prevent the process of rusting of iron a coat of zinc metal is put on top of the iron article which acts as a sacrificial element by undergoing corrosion and forms a passive oxide layer on top and thus, prevents the further corrosion of the zinc layer and in doing so it prevents the rusting of iron.
(e) Metals like sodium, potassium, calcium and magnesium are very reactive metal and thus have a very high affinity for a reaction with oxygen gas present in the atmosphere. That is why these metals are never found in their free state in nature.
Page No 27:
Question 62:
(i) Given below are the steps for extraction of copper from its ore. Write the reaction involved.
(b) Reduction of copper (I) oxide with copper (I) sulphide.
(c) Electrolytic refining
(ii) Draw a neat and well labelled diagram for electrolytic refining of copper
Answer:
(i)
(ii)
Diagram for electrolytic refining of copper
Page No 27:
Question 63:
Of the three metals X, Y and Z. X reacts with cold water, Y with hot water and Z with steam only. Identify X, Y and Z and also arrange them in order of increasing reactivity.
Answer:
X reacts with cold water so, X could be sodium or potassium metal.
Y reacts with hot water so, Y could be magnesium or calcium.
Z reacts with steam only so, Z could be Aluminium, iron or zinc.
Out of the identified metals, X is the most reactive and Z is the least reactive so, in order if increasing reactivity they could be arranged as Z < Y < X.
Page No 27:
Question 64:
An element A burns with golden flame in air. It reacts with another element B, atomic number 17 to give a product C. An aqueous solution of product C on electrolysis gives a compound D and liberates hydrogen. Identify A, B, C and D. Also write down the equations for the reactions involved.
Answer:
Sodium when burnt in air, burns with a golden flame so, element A is sodium. Since element B has an atomic number of 17 so, it is chlorine. When sodium reacts with chlorine it forms sodium chloride.
When an aqueous solution of sodium chloride is electrolysed it liberates hydrogen and chlorine gas and another aqueous product sodium hydroxide so, the compound D is sodium hydroxide.
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Question 65:
Two ores A and B were taken. On heating ore A gives CO2 whereas, ore B gives SO2. What steps will you take to convert them into metals?
Answer:
Ore A gives carbon dioxide on heating that means it is a carbonate ore. For the extraction of metal, ore A is first calcined and then reduced to get the pure metal.
Calcination: Ore A is heated in the absence of air below its melting point to get the oxide of the corresponding metal.
Reduction: The metal oxide formed after the calcination process is further reduced with coke to get pure metal.
Ore B gives sulphur dioxide on heating that means it is a sulphide ore. For the extraction of metal, ore B is first roasted and then reduced to get the pure metal.
Roasting: Ore B is heated in the presence of air below its melting point to get the oxide of the corresponding metal.
Reduction: The metal oxide formed after roasting is further reduced to with carbon to get pure metal.
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