1) 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.
Ans.(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.
2) Why should the metal sulphides and carbonates be converted to metal oxides in the
process of extraction of metal from them?
Ans. Usually metal sulphides and carbonates are converted to metal oxides in the process of extraction
of metal because metal oxides can be easily reduced to metal with the help of some common reducing agent like coke.
3) 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) Iron (III) oxide (Fe2O3 ) is used with aluminium (Al) to join railway tracks.
(b) The reaction is known as Thermite reaction.
(c) Fe2O3 (s) + 2 Al (s) → 2 Fe (s) + Al2O3 (s) + Heat
4) 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. Given, the 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).
2 Na + 2 H2O (Cold) → 2 NaOH + H2↑
Hence; X = Sodium (Na), Y = Sodium hydroxide (NaOH), Z = Hydrogen gas (H2)
5) 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.
Ans. Different forms of any element are called allotropes. Since Y is the hardest substance
so it must be diamond which is an allotrope of carbon.
Hence the non-metal X is carbon.
Another allotrope of carbon is graphite which is a very good conductor of electricity due to
the presence of free mobile electrons.
Hence X = Carbon, Y= Diamond and Z = Graphite
6) The following reaction takes place when the aluminium powder is heated with MnO2
3 MnO2 (s) + 4Al (s) → 3 Mn (l) + 2 Al2O3 (l) + Heat
(a) Is Aluminium getting reduced?
(b) Is MnO2 getting oxidized?
Ans: (a) As Al converts to Al2O3, i.e., oxygen is added to also it is getting oxidized.
(b) Now, MnO2 gets converted to Mn, i.e. oxygen is being removed from MnO2, so it is getting reduced.
7) What are the constituents of solder alloy? Which property of solder makes it suitable for
welding electrical wires?
Ans: 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 as compared to the metals hence used for
welding electrical wires.
8) 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.
Ans: Mercury is the only metal which exists in a 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
9) Give the formulae of the stable binary compounds that would be formed by the combination of following pairs of elements.
(a) Al and Cl2 (b) K and O2
Ans: (a) Al and Cl2 ⇒ AlCI3 (Aluminium chloride)
(b) K and O2 ⇒ K2O (Potassium oxide)
10) What happens when
(a) ZnCO3 is heated in the absence of oxygen?
(b) A mixture of Cu2O and Cu2S is heated?
Ans:
(a) Heating of carbonate ores in the absence of oxygen is called as calcination. Zinc carbonate (ZnCO3) also forms zinc oxide (ZnO) and carbon dioxide when it is heated in the absence of oxygen.
(b) Reaction of copper sulphide (Cu2S) and copper oxide (Cu2O) at high temperature forms copper metal and sulphur dioxide gas is expelled out.
11) Give two examples each of the metals that are good conductors and comparatively poor conductors of heat respectively.
Ans: (a) Good conductors: Aluminium and copper are good conductors of heat.
(b) Poor conductors: Titanium and mercury are poor thermal conductors.