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