NCERT Exemplar: Metals & Non-metals Notes | Study Science Class 10 - Class 10

Short Answer Type Questions

Q.1. Iqbal treated a lustrous, divalent element M with sodium hydroxide. He observed the formation of bubbles in the 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.
Ans.

• M + 2NaOH → Na₂MO₂ + H₂(g)
• M + 2HCl → MCl₂ + H₂(g)
• Bring a burning candle near the gas. 
• If it burns with a pop sound, the gas is hydrogen, and the element is a metal.
  

Q.2. During the 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?
Ans. (a) Pure silver rod will be used as cathode, and impure silver rod will be used as the anode.

(b) AgNO₃(aq) can be used as the electrolyte.
(c) Pure silver will be formed at the cathode.
At anode : Ag → Ag⁺ + e^-
At cathode : Ag⁺ + e^- → Ag

Q.3. Why should the metal sulphides and carbonates be converted to metal oxides in the process of extraction of metal from them?
Ans. It is because it is easier to reduce metal oxides to get free metals as compared to metal sulphides and metal carbonates.

Q.4. 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?
Ans. It is because HNO₃ is an oxidising agent and it gets reduced to NO if it is dilute and NO₂ if HNO₃ is concentrated, it oxidises H₂ to H₂O.

Q.5. Compound X and aluminium are used to join railway tracks.
(a) Identify the compound X.
(b) Name the reaction.
(c) Write down its reaction.
Ans. (a) ‘X ’ is Fe₂O₃.
(b) It is called thermite reaction.

(c) 
Molten iron is used to form broken railway tracks.

Q.6. 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.

Ans.

• Both sodium (Na) and potassium (K) react with cold water to give basic salt NaOH and KOH respectively. Since the molecular mass of XOH is 40, therefore, the metal X is Na. Since, the molecular mass of NaOH is 40 (23 + 16 + 1 = 40). 
• Therefore, Y is NaOH and the gas liberated during the reaction is hydrogen. Thus, Z is H₂.
  2Na + 2H₂O → 2NaOH + H₂ + Heat energy

Q.7. The following reaction takes place when aluminium powder is heated with MnO₂

(a) Is aluminium getting reduced?
(b) Is MnO₂ getting oxidised?
Ans. (a) No, aluminium is getting oxidised.
(b) No, MnO₂ is getting reduced.

Q.8. What are the constituents of solder alloy? Which property of solder makes it suitable for welding electrical wires?
Ans.

• Solder is made up of lead and tin. 
• It has low melting point, therefore, it is used for soldering (welding) electrical wires.
  

Q.9. 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.
Ans.

• ‘A’ is aluminium.
  4Al(s) + 3O₂ 2Al₂O₃(s)
• 'B' is amphoteric in nature(Al₂O₃).
  ► Al₂O₃ + 6HCl → 2AlCl₃ + 3H₂O
  ► Al₂O₃ + 2NaOH → 2NaAlO₂ + H₂O

Q.10. A metal that exists as 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.
Ans. The metal is mercury.
► 2HgS(s) + 3O₂ → 2HgO + 3SO₂(g)
► HgS(s) + 2HgO → 3Hgl(l) + SO₂(g)

Q.11. 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
Ans.
(a) 3Mg + Mg₃N₂ → Mg₃N₂
(b) 4Li + O₂ → 2Li₂O
(c) 2Al + 3Cl₂ → 2AlCl₃
(d) 4K + O₂ → 2K₂O

Q.12. What happens when
(a) ZnCO₃ is heated in the absence of oxygen?
(b) a mixture of Cu₂O and Cu₂S is heated?
Ans.
(a) 

• Zinc oxide(s) and CO₂(g) are formed.
  ZnCO₃ZnO + CO₂
• Blister copper(s) and SO₂(g) are formed.

(b) 2Cu₂O + Cu₂S(s)6Cu(s) + SO₂(g)

Q.13. A non-metal A is an important constituent of our food and forms two oxides B and C. Oxide B is toxic whereas oxide C causes global warming,
(a) Identity A, B and C.
(b) To which group of periodic table does A belong?
Ans. (a) 

• ‘A’ is carbon. 
• It forms two oxides: 
  (i) CO (B) is toxic
  (ii) Whereas CO₂ (C) causes global warming as it absorbs heat radiations from atmosphere.
  (b) ‘A’ belongs to group 14 of periodic table.

Q.14. An element A reacts with water to form a compound B which is used in whitewashing. 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.
Ans.


Q.15. 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.
Ans. M is 'Cu' It does not liberate hydrogen with dilute acid as it is less reactive than hydrogen gas.


Q.16. A solution of CuSO₄ was kept in an iron pot. After a 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.
Ans.

• Iron is more reactive than copper. 
• Therefore, it displaces copper from copper sulphate solution.
  
  
•  A portion of the iron pot got dissolved in this process and caused holes in it.

Long Answer Type Questions

Q.17. 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 0 2, 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?
Ans. (a)

• N₂ is largest constituent of air when heated with H₂ in the ratio of 1 : 3 in the presence of a catalyst (Fe) gives a gas NH₃(B).
  
  
• Nitrogen reacts with oxygen on heating to form nitrogen monoxide 'C' which gets oxidised in the presence of O₂ to nitrogen dioxide. Nitrogen dioxide dissolves in water in the presence of oxygen to form nitric acid, which is an oxidising agent.
  
  
• 'A' is N₂, 'B' isNH₃, 'C' is NO and 'D' is HN0₃.
  (b) Group 15

Q.18. Give the steps involved in the extraction of metals of low and medium reactivity from their respective sulphide ores.
Ans.

• Metal sulphide like HgS reacts with O₂ on heating to form mercuric oxide, HgO and sulphur dioxide, SO₂.
  2HgS + 3O₂  2HgO + 2SO₂
• Mercuric oxide on further heating gives Hg which can be refined by distillation.
  2HgO2Hg + O₂
• In the same manner, copper in copper glance, Cu₂S is found in nature and can be obtained from its ore by heating in air:
  2Cu₂S + 3O₂  2Cu₂O + 2SO₂
  2Cu₂O + Cu₂S → 6Cu + SO₂
• Pure copper is obtained from electrolytic refining.

(b)

• Sulphide ore like zinc blende (ZnS) on roasting in the presence of O₂ gives metal oxide. On reduction with suitable reducing agent gives metal which is impure.
• Impure metal on electrolytic refining gives pure metal.
  
  
• Pure zinc is obtained by electrolytic refining.

Q.19. Explain the following
(а) 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.
Ans. (a) It is due to the formation of oxide layer on its surface.
(b) It is because Na or Mg are strong reducing agents, therefore, carbon cannot reduce their oxides.
(c) NaCl does not conduct electricity in solid state as it does not have free ions to move in solid-state but in aqueous solution and in molten states ions are free to move.
(d) Iron articles are galvanised to protect them from rusting.
(e) It is because these metals are highly reactive and occur in the form of their compounds.

Q.20. 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.

• ‘A’ is sodium as it bums with golden flame in air.
• ‘B ’ (17) has electronic configuration 2, 8, 7 so ‘B ’ is chlorine
  
  ‘A’ is Na, ‘B’ is Cl_2, ‘C’ is NaCl and _{‘D’ is NaOH.}

Q.21. 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 then into metals?
Ans.

• Ore A gives CO₂, therefore, it is a carbonate ore. Ore ‘A’ is first subjected to calcination, followed by reduction.
  MCO₃MO + CO₂
  MO + C  M + CO
• Ore B gives SO₂, therefore, it is a sulphide ore. Ore B is first subjected to roasting followed by reduction.
  2MS + 3O₂  2MO + 2SO₂
  MO + C  M + CO