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NIOS Class 12 Chemistry Chapter 20 p-block Elements and their Compounds – II
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p-block Elements and their Compounds – II
Chapter: 20
| Module – VI: Chemistry of Elements |
INTEXT QUESTIONS 20.1
1. Give one example each of basic oxide, acidic oxide and amphoteric oxide.
Ans: Basic oxide : CaO; acidic oxide : SO₂ ; amphoteric oxide : ZnO.
2. Classify the following oxides into acidic, basic or amphoteric oxides : K₂O, SiO₂, SO₂, FeO, Al₂O₃, ZnO, CrO₃.
Ans: Acidic oxide : SiO₂, SO₂, CrO₃
Basic oxide : K₂O, FeO
Amphoteric oxide : Al₂O₃, ZnO
3. Give chemical equations to illustrate the amphoteric behaviour of ZnO.
Ans: ZnO + H₂SO₄ → ZnSO₄ + H₂O
ZnO + 2NaOH → Na₂Zn O₂ + H₂O
4. Name the compound formed when the oxide of an element of Group 1 or 2 reacts with acid?
Ans: An oxide of group 1, K₃O and of Gr 2 BaO
K₂O + 2HCl ⎯⎯→ 2KCl + H₂O
BaO + H₂SO₄ ⎯⎯→ BaSO₄ + H₂O
5. Oxygen is a gas but Sulphur is solid why?
Ans: Oxygen has multiple bonds but sulphur has single bond.
INTEXT QUESTIONS 20.2
1. What are ozonides? What happens when an ozonide is hydrolysed?
Ans: When ethene combines with O₃, an ozonide is formed, thus:
On hydrolysis it gives HCHO,
2. Write the reactions which occur when ozone reacts with (i) ferrous sulphate (ii) stannous chloride.
Ans: (i) 2FeSO₄ + O₃ + H₂SO₄ ⎯→ Fe₂(SO₄)₃ + H₂O + O₂
(ii) 3SnCl₂ + O₃ + 6HCl ⎯→ 3SnCl₄ + 3H₂O.
3. Which is more soluble in water, oxygen or ozone?
Ans: Ozone is 10 times more soluble than O₂.
4. Draw the structure of ozone molecule, O₃.
Ans:
5. What is meant by “tailing of mercury”? How is it removed?
Ans: Mercury loses its convex meniscus and leaves a “tail” or a trail of minute droplets on a glass surface when exposed to ozone. This is due to the formation of mercurous oxide. The tailing effect can be removed by washing the mercury with a dilute acid.
INTEXT QUESTIONS 20.3
1. Write a reaction to show the:
(i) Oxidizing property of sulphuric acid.
(ii) Dehydrating property of sulphuric acid.
Ans: (i) Oxidizing property of conc. H₂SO₄
Cu + 2H₂SO₄ ⎯→ CuSO₄ + SO₂ + 2H₂O
(ii) Dehydrating property : It removes water from sugar.
C12H₂₂O₁₁ + H₂SO₄ ⎯⎯→ 12C + 11 H₂O
2. In the manufacture of sulphuric acid by Contact process, SO₃ is dissolved in conc. H₂SO₄ and not in water. Why?
Ans: A corrosive mist of sulphuric acid is formed.
3. Write the reaction that takes place in the presence of a catalyst in the contact Process.
Ans:
INTEXT QUESTIONS 20.4
1. Name the most electronegative halogen.
Ans: Fluorine.
2. Name the halogen that can react with an inert gas.
Ans: Fluorine.
3. Write a chemical reaction used for the laboratory preparation of chlorine.
Ans: 2 NaCl + 3H₂SO₄ + MnO₂ → MnSO₄ + 2NaHSO₄ + 2H₂O + Cl₂.
4. Arrange the hydroacids of halogens in the decreasing order of their strength.
Ans: Hl > HBr > HCl > HF.
5. What group of carbon compounds is supposed to cause ozone depletion?
Ans: Chlorofluorocarbons (or freons).
TERMINAL EXERCISES
1. Which one of the following oxides can react with an acid as well as with an alkali : SO₂, CaO, ZnO, MgO?
Ans: The oxide that can react with both an acid and an alkali is ZnO.
ZnO + 2HCl → ZnCl₂ + H₂O (reaction with acid)
ZnO + 2NaOH → Na₂ZnO₂ + H₂O (reaction with alkali)
ZnO exhibits amphoteric properties, reacting with both acids and bases.
2. Write two oxides which do not react with either acids or alkalies. Which type of oxides are they?
Ans: Two examples of oxides that do not react with either acids or alkalis are:
(i) CO (Carbon Monoxide)
(ii) N₂O (Nitrous Oxide)
These oxides are classified as neutral oxides, meaning they do not exhibit acidic or basic properties and do not react with acids or bases under normal conditions.
3. Is ozone an allotrope of oxygen? Which is more soluble in water oxygen or ozone?
Ans: Yes, ozone (O3) is an allotrope of oxygen (O2). Ozone is significantly more soluble in water than oxygen, being roughly 13 times more soluble at 25°C.
4. What is the state of hybridization of the central oxygen atom in O₃ molecule?
Ans: The central oxygen atom in the ozone (O₃) molecule is sp² hybridized. This hybridization allows for the bent or V-shape structure of the ozone molecule, with a bond angle of approximately 117°.
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