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18.Give two examples each of the metals that are good conductors and poor conductors of heat respectively. 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.
19.The metal which exist as a liquid at room temperature is mercury.
Non-metal which exist as a liquid at room temperature is bromine.
20.
Since an oxide of element is acidic in nature, therefore, "A" will be a non - metal because for the non-metal oxides, their acidity is usually thought of in terms of the acidic solutions formed when they react with water. For example, sulphur trioxide reacting to give sulphuric acid.
21.Non-metal a is nitrogen because it is the largest constituent of air which constitute around 78% of the gases. B is Ammonia, C is Nitrogen dioxide D is Nitric acid. When heated with H2 in 1:3 ratio in the presence of catalyst (Fe) following reaction takes place. 3N2 + 3H2 → 2NH3 On heating Nitrogen with O2 it gives nitrogen-di-oxide N2 + 3O → 2NO2 When nitrogen dioxide is passed into water in the presence of air it gives an Nitric acid NO2 + H2O → HNO3 b) Nitrogen belong to group 15.
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14. Most of the metals do not react with HNO₃ because nitric acid is a strong oxidizing agent. Hence, when metals (except Mn and Mg) are treated with nitric acid; hydrogen gas is not liberated.
Mg + 2HNO₃ → Mg(NO₃)₂ + H₂
15. X is coal.
Y is a diamond .
Z is graphite.
16. Metal ‘A’ is Aluminium (Al) which is used in the thermite process.
Al reacts with oxygen to form aluminum oxide, Al2O3 (B), which is amphoteric in nature.
4Al + 3O₂ → 2Al₂O₃
The chemical equation of the reaction of oxide Y with HCl is:
Al₂O₃ + 6HCl → 2AlCl₃ + 3H₂O
The chemical equation of the reaction of oxide Y with NaOH is:
Al₂O₃ + 2NaOH → 2NaAlO₂ +H₂O
17. (a) 'A' is Carbon
'B' is Carbon monoxide
'C' is Carbon dioxide
(b) Carbon (or A) has atomic number 6. Its electronic configuration is 2,4. It is present in the 14th group of the periodic table.
18. Good conductors: Aluminium and Copper
Poor conductors: Lead and Mercury
19. (a) Metal that exists in a liquid state at room temperature = Mercury
Non-metal that exists in a liquid state at room temperature = Bromine
(b) Metals having melting point less than 310 K = Caesium and Gallium
20. Non-metallic oxides are acidic in nature.
Whereas metallic oxides are basic in nature.
∴ 'A' is a non-metal
21. (a) 'A' is N₂ (Nitrogen)
'B' is NH₃ (Ammonia)
'C' is NO (Nitrogen Dioxide)
'D' is HNO₃. (Nitric Acid)
(b) Element A belongs to group -15 of the periodic table
22. 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.
Al + HNO₃ → Al(NO₃)₃ + NO₂ + H₂O
22. 'X' reacts with cold water.
Hence , the element is "Calcium"
Ca + H₂O → Ca(OH)₂ + H₂
'Y' reacts with hot water,
Hence, the element is "Magnesium"
Mg + H₂O → Mg(OH)₂ + H₂
'Z' reacts with steam only.
Hence , the element is "Iron"
Fe + H₂O → Fe₂O₃+ H₂
- Arranging in ascending order (increasing order of reactivity)
Fe < Mg < Ca
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