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
Answer: Magnesium nitride (Mg3N2)
(b) Li and O2
Answer: Lithium oxide (Li2O)
(c) Al and Cl2
Answer: Aluminium chloride (AlCl3)
(d) K and O2
Answer: Potassium oxide (K2O)
Question 49: What happens when
(a) ZnCO3 is heated in the absence of oxygen?
Answer: When zinc carbonate is heated in the absence of oxygen, zinc oxide and carbon dioxide are produced.
ZnCO3 ⇨ ZnO + CO2
(b) A mixture of Cu2O and Cu2S is heated?
Answer: When a mixture of copper oxide and copper sulphide is heated, pure copper is obtained.
2Cu2O + Cu2S ⇨ 6Cu + SO2
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
Answer: The clue that C causes global warming shows it is carbon dioxide. A is carbon, B is carbon monoxide and C is carbon dioxide.
(b) To which Group of Periodic Table does A belong?
Answer: Carbon belongs to Group 14
Question 51: Give two examples each of the metals that are good conductors and poor conductors of heat respectively.
Answer: Good conductors: Iron and copper
Poor conductors: Lead and mercury
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: Mercury (metal) and Iodine (non-metal) exist in liquid state at room temperature. Gallium and caesium are metals with melting points less than 310 K.
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. The involved reactions are as follows:
Ca + 2H2O ⇨ Ca(OH)2 + H2
Ca(OH)2 ⇨ CaO + H2O
CaO + H2O ⇨ Ca(OH)2
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: Clue from question 42 shows that compound B is sodium hydroxide. Hence A is sodium and C is sodium aluminate.
2Na + 2H2O ⇨ 2NaOH + H2 + Heat
Al2O3 + 2NaOH ⇨ 2NaAlO2 + H2O
Question 55: Give the reaction involved during extraction of zinc from its ore by
(a) Reaction during roasting of zinc ore
Answer: 2ZnS + 3O2 ⇨ 2ZnO + 2SO2
(b) Reaction during calcination of zinc ore
Answer: ZnCO3 ⇨ ZnO + CO2
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: M is copper and black coloured product is copper (II) oxide.
2Cu + O2 ⇨ 2CuO
Question 57: An element forms an oxide A2O3 which is acidic in nature. Identify A as a metal or non-metal.
Answer: We know that oxides of non-metals are acidic in nature and A is a non-metal.
Question 57: 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: Iron is more reactive than copper. Hence, iron displaced copper from copper sulphate solution. This reaction resulted in formation of holes in the iron pot. The following equation shows this reaction.
CuSO4 + Fe ⇨ FeSO4 + Cu
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