NCERT Exemplar Class 10 Science Chapter 3 Metals And Non-Metals
NCERT Exemplar Class 10 Science Chapter 3 Metals And Non-Metals are part of NCERT Exemplar Class 10 Science. Here we have given NCERT Exemplar Class 10 Science Chapter 3 Metals And Non-Metals.
Multiple Choice Questions (MCQs)
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. (c)
Explanation: Metallic luster is the characteristic feature of metals that is due to presence of free electrons.
Question. 2 The ability of metals to be drawn into thin wire is known as:
(a) ductility
(b) malleability
(c) sonorousity
(d) conductivity
Answer. (a)
Explanation: Ductility can be defined as the property of metals to drawn in thin wires by application of force on them.
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. (d)
Explanation: Some of the most common properties of Aluminium are good thermal conductivity, malleability, light weight and high melting point which make it useful for making cooking utensils.
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. (d)
Explanation: Na, Ca and Mg are reactive metals and quickly react with water. At room temperature, the reaction of Fe is very slow but red hot iron reacts with steam to form Fe3O4 with hydrogen gas.
3Fe + 4H2O → Fe3O4 + 4 H2
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. (c)
Explanation: Prolong heating of red hot iron with steam form Fe3O4 with hydrogen gas.
3Fe + 4H2O → Fe3O4 + 4H2
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. (d)
Explanation: Calcium reacts less violently with water producing the bubbles of hydrogen gas along with calcium hydroxide (Ca(OH)2).
Ca (s) + 2H2O (l) → Ca(OH)2 (aq) + H2 (g)↑
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) HCI
(c) HNO3
(d) All of these
Answer. (c)
Explanation: Nitric acid (HNO3) is a strong oxidizing agent so it does not give hydrogen gas with metals (except Mn and Mg). As hydrogen gas is formed in the reaction HNO3 oxidizes this hydrogen to water.
Question. 8 The composition of aqua-regia is
(a) Dil.HCI : Conc. HNO3 ↔ 3 : 1
(b) Conc. HCI: Dil. HNO3 ↔ 3 : 1
(c) Conc. HCl: Conc. HNO3 ↔ 3 : 1
(d) Dil. HCl: Dil. HNO3 ↔ 3 : 1
Answer. (c)
Explanation: Aqua-regia is a mixture of concentrated HCl and concentrated HNO3 in 3 : 1 ratio.
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. (b)
Explanation: Ionic compounds are formed by combination of cation and anions. HCl and CCl4 are formed by equal sharing of electrons between atoms in the molecule. Here HCl is a polar covalent compound and CCI4 is a non-polar covalent compound.
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. (b)
Explanation: Ionic compounds can conduct electricity in molten or aqueous state due to presence of free ions. In solid state, no free or mobile ions are available for conducting electricity.
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. (c)
Explanation: Gold and silver (Au and Ag) are also known as Noble metals as they are less reactive and exist in their native state in nature.
CBSE Class 10 NCERT Textbooks & NCERT Solutions
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) (ii) and (iv)
Answer. (a)
Explanation: Alkali metals are very reactive so cannot refine with the help of electrolytic refining process.
Question. 13 Silver articles become black on prolonged exposure to air. This is due to the formation of
(a) Ag3N
(b) Ag3O
(c) Ag2S
(d) Ag2S and Ag3N
Answer. (c)
Explanation: Silver metal reacts with atmospheric sulphur compounds like H2S gas and form black coating of Ag2S over surface.
Question. 14 Galvanisation is a method of protecting iron from rusting by coating it with a thin layer of
(a) Gallium
(b) Aluminium
(c) Zinc
(d) Silver
Answer. (c)
Explanation: Zinc (Zn) metal is used to protect iron surface from rusting.
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. (a)
Explanation: Stainless steels are formed with the addition of high proportion of chromium and nickel to iron.
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. (b)
Explanation: Copper reacts with moist carbon dioxide in the air and form green colour basic copper carbonate.
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. (d)
Explanation: At room temperature, mercury is found in liquid state.
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. (d)
Explanation: Usually alkali and alkaline earth metals can be extracted by electrolysis of their salts in molten state.
Question. 19 Generally non-metals are not lustrous. Which of the following non-metals is lustrous?
(a) Sulphur
(b) Oxygen
(c) Nitrogen
(d) Iodine
Answer. (d)
Explanation: Iodine is a non-metal with lustrous appearance and exists in solid state.
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. (b)
Explanation: Least reactive metal can be displaced from its solution by other three metals. Silver is least reactive out of given four metals.
Question. 21 2 mL each of conc. HCl, HNO3, and a mixture of conc. HCl. and conc. HNO3, in the ratio of 3 : 1 were taken in test tubes labeled 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. The metal could be
(a) Al
(b) Au
(c) Cu
(d) Pt
Answer. (b), (d)
Explanation: A mixture of conc. HCI and conc. HNO3 in the ratio of 3: 1 forms aqua-regia which can dissolve gold (Au) and platinum (Pt).
Question. 22 An alloy is
(a) An element
(b) A compound
(c) A homogeneous mixture
(d) A heterogeneous mixture
Answer. (c)
Explanation: A homogeneous mixture of different metals or a metal and a non-metal is called as alloy.
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) and (iv)
Answer. (b)
Explanation: There is a positively charged anode and negatively charged cathode in an electrolytic cell.
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. (a)
Explanation: During electrolytic refining the pure zinc metal is deposited on cathode.
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. (b)
Explanation: Sodium is a soft, reactive alkali metal.Question. 26 Alloys are homogeneous mixtures of a metal with a metal or non-metal. Which among the following alloys contain non-metal as one of its constituents?
(a) Brass
(b) Bronze
(c) Amalgam
(d) Steel
Answer. (d)
Explanation:
(a) Brass- Copper and zinc
(b) Bronze- Copper and tin
(c) Amalgam- Mercury with other metals
(d) Steel- Iron with carbon
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. (b)
Explanation: Magnesium metal does not react with cold water but reacts with both hot water and steam to form magnesium hydroxide and hydrogen gas.
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. (d)
Explanation:
(a)Stainless steel – Fe with C
(b) Alnico – Al, Ni and Co
(c) Solder – Pb and Sn
(d) Zinc amalgam – Zn with Hg
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. (b)
Explanation: Since Z is formed from X and Y by complete transfer of electrons therefore Z should be ionic compound which must have high melting point and conductivity in molten state and usually occur as solids.
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. (d)
Explanation: Metals have 1 or 2 electrons in their valance shell whereas non-metals have 5-7 valence electrons. Here X has octet configuration so it should be a Noble gas.
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. (c)
Explanation: Some of the metals like Aluminium (Al) metal forms amphoteric oxide (A12O3) which can behave like acid as well as base.
Question. 32 Generally non-metals are non-conductors of electricity. Which of the following is a good conductor of electricity?
(a) Diamond
(b) Graphite
(c) Sulphur
(d) Fullerene
Answer. (b)
Explanation: Graphite is one of the allotropes of carbon which shows layers arrangement of carbon atoms. The fourth valence electron of each carbon is free to move that makes it good conductor of electricity.
Question. 33 Electrical wires have a coating of an insulating material. The material, generally used is
(a) Sulphur
(b) Graphite
(c) PVC
(d) All can be used
Answer. (c)
Explanation: An insulating substance is required to coat the electrical wire such as PVC.
Question. 34 Which of the following non-metals is a liquid?
(a) Carbon
(b) Bromine
(c) Phosphorus
(d) Sulphur
Answer. (b)
Explanation: Bromine is a non-metal which exists in liquid state.
Question. 35 Which of the following can undergo a chemical reaction?
(a) MgSO4 + Fe
(b) Zn SO4 + Fe
(c) MgSO4 + Pb
(d) Cu SO4 + Fe
Answer. (d)
Explanation: According to reactivity series, more reactive metal can displace less reactive metal from its compound. Fe is more reactive compare to copper so it can displace copper from its compound, copper sulphate. The reactivity order for given metals are;
Mg < Zn < Fe < Pb < Cu
Question. 36 Which one of the following figures correctly describes the process of electrolytic refining?
Answer. (c)
Explanation: In electrolytic refining process, impure metal forms the anode which is positive electrode whereas pure metal forms the cathode which is negative electrode.
In the given image, apparatus for electrolytic refining of copper metal is being shown in which copper from impure anode dissolves into the solution and Cu2+ ions from the solution are deposited on the cathode.
Short Answer Type Questions
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 be identify the produced gas. Write chemical equations for both the reactions.
Answer.
The divalent element must be some metal which releases hydrogen gas with both acid and bases. Bring a burning splinter near the gas, it will burn with a pop sound, hence it must be hydrogen gas. The divalent element could be zinc. Chemical equations for both the reactions are;
Question. 38 During extraction of metals, electrolytic 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) Thin strip of pure silver is made the cathode and impure silver block is made the anode.
(b) Any salt solution of silver like AgNO3 can be used as electrolyte.
(c) On passing electric current, from the electrolyte metal ions discharge on the cathode whereas metal ions from impure metal dissolves and goes into the electrolyte solution.
Question. 39 Why should the metal sulphides and carbonates be converted to metal oxides in the process of extraction of metal from them?
Answer.
Usually metal sulphides and carbonates are converted to metal oxides in the process of extraction of metal. This is because metal oxides can easily reduce to metal with the help of some common reducing agent like coke.
Ores of metal can converted to metal oxides with the help of calcination or roasting which depends on the nature of ore. For example, metal carbonate can convert to metal oxide by calcinations whereas roasting is used for metal sulphide.
Question. 40 Generally when metals are treated with mineral, acids. Hydrogen gas is liberated but when metals (except Mn and Mg) are treated with HNO3, hydrogen is not liberated, why?
Answer.
Unlike other acids, reaction of nitric acid is little different because it is a good oxidizing agent.
As hydrogen gas is formed during the reaction of nitric acid with metals, acid reacts with hydrogen gas and converts it to water. And nitric acid gets reduced to NO2 or NO or N2O.
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) Iron (III) oxide (Fe2O3) is used with aluminium (Al) to join railway tracks.
(b) The reaction is known as Thermite reaction or Alumino thermy process.
(c) Fe2O3(s) + 2 Al(s) → 2 Fe(l) + Al2O3 (s) + Heat
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.
Given, molecular formula of Y = XOH
And molecular mass OF Y = 40.
So, atomic mass of metal X would be;
M + 16 + 1 = 40 ⟹ M = 40 − 17=23
Metal with atomic mass 23 is sodium and reaction of it with cold water will form sodium hydroxide (NaOH).
2Na + 2H2O (Cold) → 2NaOH + H2↑
Hence; X = Sodium (Na), Y = Sodium hydroxide (NaOH), Z = Hydrogen gas (H2)
Question. 43 A non-metal X exists in two different forms Y and Z. Y is hardest natural substance, whereas Z is a good conductor of electricity. Identify X, Y and Z.
Answer.
Different forms of any element are called as allotropes. Since Y is the hardest substance so it must be diamond which is an allotrope of carbon. Hence non-metal X is carbon. Another allotrope of carbon is graphite which is very good conductor of electricity due to presence of free mobile electrons.
Hence; X = Carbon, Y= Diamond and Z = Graphite
Question. 44 The following reaction takes place when aluminium powder is heated with MnO2
3MnO2 (s) + 4Al (s) 3Mn (l) + 2Al2O3 (l) + Heat
(a) Is aluminium getting reduced?
(b) Is MnO2 getting oxidized?
Answer.
(a) As Al converts to Al2O3, i.e., oxygen is added to Al so it is getting oxidized.
(b) Now MnO2 gets converted to Mn, i.e. oxygen is being removed from MnO2, so it is getting reduced.
Question. 45 What are the constituents of solder alloy? Which property of solder makes it suitable for welding electrical wires?
Answer.
Solder is a fusible metal alloy of lead (Pb) and tin (Sn). It contains 40% lead and 60% of Sn metal.
Solder has a low melting point around 90°C to 450 °C as compared to the metals used in forming electrical wires. So, it acts as bridge between two metal pieces, hence used for welding electrical wires.
Question. 46 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.
Ans. Aluminium (Al) is used in thermite process so metal A is Aluminium. The reaction of Al with oxygen forms aluminium oxide Al2O3 which is amphoteric in nature as it can exhibit acidic as well as basic nature.
4Al (s)+ 3O2 (g) → 2Al2O3 (s)
Hence; A = Aluminium and B = Aluminium oxide
Reactions of aluminium oxide with HCl and NaOH are as given below;
Al2O3 (s) + 6 HCl (aq)→ 2AlCl3 (aq) + 3 H2O (l)
Al2O3 (s) + 2NaOH (aq)→ 2NaAlO2 (aq) + H2O (l)
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. Give the reactions involved.
Answer.
Mercury is the only metal which exists in liquid state at room temperature. It is usually extracted from its sulphide ore, mercury (II) sulphide or cinnabar (HgS) by the process of roasting. Hence;
Metal = Mercury and Ore = Cinnabar
Roasting of ore occurs in the presence of air and form metal oxide which further reduce to metal.
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) Mg and N2 – Mg3N2 (Magnesium nitride)
(b) Li and O2– Li2O (Lithium oxide)
(c) Al and Cl2– AlCI3 (Aluminium chloride)
(d) K and O2– K2O (Potassium oxide)
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) Heating of carbonate ores in the absence of oxygen is called as calcinations. Zinc carbonate (ZnCO3) also forms zinc oxide (ZnO) and carbon dioxide when it is heated in the absence of oxygen.
This process is used to convert carbonate ores to metal oxides and also helps to remove moisture and volatile impurities.
(b) Reaction of copper sulphide (Cu2S) and copper oxide (Cu2O)at high temperature forms copper metal and sulphur dioxide gas is expelled out.
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) Non-metal A must be carbon as it forms two oxides; carbon monoxide (CO) and carbon dioxide. Out of these two oxides; one is toxic that is CO and another is responsible for global warming so it must be CO2 (carbon dioxide).
Hence; A = Carbon, B = Carbon monoxide and C = Carbon dioxide.
(b) The electronic configuration of carbon is 2, 4. So there are 4 valence electrons and group number should be 10 + number of valence electrons. So carbon belongs to 14th group of the periodic table.
Question. 51 Give two examples each of the metals that are good conductors and comparatively poor conductors of heat respectively.
Answer.
(a)Good conductors: Aluminium and copper are good conductors of heat.
(b)Poor conductors: Titanium and mercury are poor thermal conductors.
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.
(a) Metal that exists in liquid state at room temperature = Mercury
(b) Non-metal that exists in liquid state at room temperature = Bromine
(c) Metals having melting point less than 310 K = Caesium (28.5oC) and Gallium (29.76°C)
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.
The compound that is used in white wash is calcium hydroxide. So the element must be calcium that reacts with water to form calcium hydroxide. Heating of calcium hydroxide forms calcium oxide which again converts to hydroxide with the reaction of water.
Hence; A = Ca, B = Ca(OH)2, C = CaO
Reactions involved are:
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 reactions involved.
Answer.
Alkali metals form MOH type of metal hydroxides with water. The molecular mass of hydroxide, B is 40 therefore mass of metal can be calculated as;
MOH = x + 16 + 1 = 40 ⟹ x = 23
Thus the atomic mass of alkali metal is 23. So it must be sodium that reacts with water to form sodium hydroxide (NaOH).
2Na + 2H2O → 2NaOH (aq) + H2 (g)↑
Reaction of sodium hydroxide with aluminium oxide (Al2O3) gives soluble sodium aluminate (NaAlO2).
Al2O3 + 2NaOH → 2NaAlO2 + H2O
Hence; A = Sodium, B = Sodium hydroxide and C = Sodium aluminate
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.
(a) Roasting of zinc ore:
- Conversion of sulphide ore to metal oxide can be done with the help of roasting which is a heating process in the presence of air below melting point of metal. Roasting of zinc ore like zinc sulphide forms zinc oxide and sulphur dioxide.
- This metal oxide formed above can further reduce to metallic zinc in the presence of coke.
(b) Calcination of zinc ore:
- Calcination is a heating process for carbonate ore in the absence of air. Zinc carbonate (ZnCO3) or calamine converts to zinc oxide and carbon dioxide.
- Then, like roasting, ZnO again reduces to metallic zinc in the presence of coke at high temperature.
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.
Because of less reactivity, copper metal does not release hydrogen gas with acid.
Cu(s) + HCl → No reaction
Hence metal M is copper.
Reaction of copper with oxygen on prolonged heating to form a black substance copper (II) oxide (CuO).
2Cu(s) + O2 (g) → 2CuO(s)
Question. 57 An element forms an oxide A2O3 which is acidic in nature. Identify A as a metal or non-metal.
Answer.
Metals usually form basic oxides like BaO, MgO, Na2O etc. Unlike metals, non-metals tend to form acidic oxides.
As we move from left to right in the periodic table, the acidity of oxides increases. So the element which forms acidic oxide must be non-metallic element.
The formula for oxide is A2O3 means the charge on element must be +3 or element should have 3 valence electrons that is boron and formula for oxide would be B2O3.
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.
In reactivity series, iron is placed above copper. So we can say that iron is more reactive compare to copper and it can displace copper from its compounds.
When copper sulphate solution is placed in an iron pot, iron reacts with copper sulphate and form iron sulphate with copper.
So the blue colour of copper sulphate solution fade to light green due to formation of iron sulphate and holes are produced at places where iron metal has reacted.
Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s)
Long Answer Type Questions
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 the periodic table does this non-metal belongs?
Ans. The largest constituent of air is nitrogen gas so the A must be nitrogen gas. Reaction of nitrogen with hydrogen in the presence of Fe catalyst forms ammonia (NH3) gas. It is known as Haber process.
Ammonia reacts with water to give nitric oxide (NO) which further oxidized to form NO2.
Reaction of oxides with water in the presence of air (O2) results nitric acid (HNO3).
4NO2 + H2O + O2 → 4HNO3
Hence; A = Nitrogen, B = Ammonia, C = Nitrogen dioxide and D = Nitric acid
(b) Nitrogen has electronic configuration 2, 5. Thus with having 5 valence electrons, nitrogen belongs to group 15 of periodic table.
Question. 60 Give the steps involved in the extraction of metals of low and medium reactivity from their respective sulphide ores.
Ans.
(a) Extraction of less reactive metals like mercury:
(i) Roasting- Heating of metal sulphide in the presence of excess of air to form metal oxide.
(ii) Reduction- Metal oxide can be reduced to metal in the presence of reducing agent at high temperature.
(b) Extraction of metals with medium reactivity like zinc:
(i) Roasting- Heating of metal sulphide in the presence of excess of air to form metal oxide.
(ii) Reduction- Metal oxide can be reduced to metal in the presence of reducing agent like coke or aluminium at high temperature.
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 galvanized.
(e) Metals like Na, K, Ca and Mg are never found in their free state in nature.
Ans.
(a) Since nitric acid is an oxidizing agent so it reacts with aluminium and forms a layer of aluminium oxide over metal surface which further reduces the reactivity of metal.
(b) Alkali and alkaline earth metals are very reactive and readily react with oxygen to form their stable oxides. The reduction of these metallic oxides with carbon requires very high temperature and at that temperature metals react with carbon to form their corresponding carbides. Hence they cannot reduce with the help of carbon as reducing agent.
(c) NaCl is an ionic compound. In solid state, oppositely charged ions are held tightly with strong metallic bond. So neither metal ions nor free electrons can move from their position. Therefore NaCl and other ionic compounds cannot conduct electricity in their solid state. In molten state or in aqueous, the free electrons and metal ions are free enough to carry charge which makes them good conductor.
(d) Galvanisation is a process of formation of thin layer over metal surface. It prevents further contact of metal surface with atmosphere and reduces the corrosion level. So iron articles are galvanized by making a thin layer of zinc over them. Since zinc is more reactive than iron so it will react first and protect iron surface.
(e) Na, K, Ca and Mgare alkali and alkaline earth metals. They are most reactive metal and readily react with atmospheric oxygen and other gases. Therefore they are found in nature in the form of their compounds.
Question. 62 (a) Given below are the steps for extraction of copper from its ore. Write the reaction involved.
(i) Roasting of copper (I) sulphide.
(ii) Reduction of copper (I) oxide with copper (I) sulphide.
(iii) Electrolytic refining
(b) Draw a neat and well labeled diagram for electrolytic refining of copper.
Ans.
(a)
(b) The diagram showing the electrolytic refining of copper-
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.
Ans. X reacts with cold water so it must be very reactive like alkali metals, sodium. Sodium reacts with water to form sodium hydroxide and hydrogen gas.
2Na + 2H2O → 2NaOH + H2
Y metal can react with hot water so it must be little less reactive than X. So Y can be magnesium (Mg) which reacts with hot water to form magnesium hydroxide.
Mg + 2H2O → Mg(OH)2 + H2
Metal which reacts with steam must be iron that forms iron (III) oxide with steam.
3Fe + 4H2O → Fe3O4 + 4H2
Hence the increasing order of reactivity of given metals is;
Z (Fe)< Y (Mg) < X (Na)
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.
Ans. Element ‘A’ that burns with golden flame is sodium (Na). Element ‘B’ with atomic number 17 is chlorine (Cl).
Sodium and chlorine react to form sodium chloride (NaCl) which is an ionic compound.
2 Na (s) + Cl2 (g) → 2NaCl (s)
The aqueous solution of sodium chloride, also called as brine when goes through electrolysis, forms sodium hydroxide (NaOH), hydrogen and chlorine gas.
Hence; A = Sodium (Na), B = Chlorine (Cl), C = Sodium chloride (NaCl), D = Sodium hydroxide (NaOH)
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?
Ans. If an ore gives carbon dioxide gas on heating it means it is a carbonate ore. So it should go with calcination step in which metal ore is heated below its melting point in the absence or limited amount of air. Similarly, calamine (ZnCO3) is heated to give zinc oxide (ZnO) and carbon dioxide.
Zinc oxide can convert to metal in the presence of reducing agent like coke.
Another ore, B gives SO2 so it must be a sulphide ore. Metal can be extracted from suphide ore with the help of roasting which is a heating process in the presence of air. Like copper(I) sulphide is heated in the presence of oxygen to give copper (I) oxide and sulphur dioxide gas.
Later copper (I) oxide (Cu2O) and copper (I) sulphide (Cu2S) heated together to form copper metal and sulphur dioxide gas is expelled out.
