Metals and Non-metals
NCERT Exemplar Problems
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
Answer: A is nitrogen (the largest component of air), B is ammonia, C is nitrogen dioxide and D is nitric acid (a strong oxidizing agent).
(b) To which group of periodic table does this non-metal belong?
Answer: Nitrogen belongs to group 15.
Question 60: Give the steps involved in the extraction of metals of low and medium reactivity from their respective sulphide ores.
Answer: Extraction of Mercury: Mercury is a metal of low reactivity. Cinnabar, i.e. mercury (II) sulphide is the ore of mercury. It is heated in air so that it is oxidized to produce mercury (II) oxide. After that, mercury oxide is reduced to obtain mercury. The following reactions are involved in this process.
2HgS + 3O2 ⇨ 2HgO + 2SO2
Extraction of metals of medium reactivity series: The metals in the middle of the reactivity series are also extracted by roasting; followed by reduction but the methods are somewhat different.
Extraction of Zinc: Zinc ire in the middle of the reactivity series. It is found in the form of zinc blende which is zinc oxide. It is first heated in the presence of air to obtain zinc oxide. This process can be shown by following equation.
2ZnS + 3O2 ⇨ 2ZnO + 2SO2
After that, zinc oxide is reduced to obtain pure zinc metal. The reduction is done in the presence of carbon. This can be shown by following equation.
ZnO + C ⇨ Zn + CO
Question 61: Explain the following
(a) Reactivity of Al decreases if it is dipped in HNO3
Answer: When aluminium is dipped in nitric acid a layer of aluminium oxide is formed on the metal. This happens because nitric acid is a strong oxidizing agent. The layer of aluminium oxide prevents further reaction of aluminium. Due to this, the reactivity of aluminium decreases.
(b) Carbon cannot reduce the oxides of Na or Mg
Answer: Sodium and magnesium have higher affinity towards oxygen than towards carbon because these are highly reactive metals. Hence, 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.
Answer: Ionic compounds do not conduct electricity in solid state but they conduct electricity in aqueous solution and in molten state. Hence, this property is shown by sodium chloride.
(d) Iron articles are galvanised.
Answer: Iron articles are galvanized to prevent rusting of iron. After galvanization, the layer of zinc works as protective layer.
(e) Metals like Na, K, Ca and Mg are never found in their free state in nature.
Answer: Metals, like Na, K, Ca and Mg are highly reactive metals and hence they are not found in their free state in nature.