Class 11th

9.31. (H⁺ and OH⁻ ions) of water molecule react with a compound to form products. For example:

NaH+H₂O → NaOH+H₂

Hydration is defined as the addition of one or more water molecules to ions or molecules to form hydrated compounds. For example:

CuSO₄+5H₂O → CuSO₄.5H₂O

9.30. No, D₂O is injurious to human beings, plants and animals.

9.29. Water is highly polar in nature. That is why it has high dielectric constant and high dipole moment. Because of these properties, water is a universal solvent.

Water is good solvent for ionic compounds but poor solvent for covalent compounds. It can hydrolyse ionic compounds.

9.28.  (i) Major part of all living system is made of water.

(ii) It constitutes about 65 – 70% of body weights of animals and plants.

(iii) Some properties of water like high specific heat, thermal conductivity, surface tension, high polarity allow water to play a major role in biosphere.

(iv) Because of high heat of vaporisation it is responsible to regulate temperature of living beings.

(v) It is an excellent fluid for the transportation of minerals and nutrients in plants.

(vi) It is also required for photosynthesis in plants.

9.27. No, demineralised or distilled water is not fit for drinking purposes. It can be made useful by adding required amount of ions which are useful for our body.

9.26. Water free from salts and minerals is called Demineralized water. Ion exchange method is used for this process. The ions present in the water bind to the positively or negatively charged sites on a resin when water is passed through the column packed with resin.

9.25. H₂O₂ as an oxidising agent:
2Fe²⁺  (aq) + 2H⁺ (aq) +H₂O₂ (aq) → 2Fe³⁺  (aq) + 2 H₂O (l)

H₂O₂ as a reducing agent:
I₂ (s) + H₂O₂  (aq) + 2OH^–  (aq) → 2I^–  (aq) + 2 H₂O (l) + O₂ (g)

9.24. Water is amphoteric in nature because it acts as an acid as well as a base.

Amphoteric nature of water is represented by following chemical reactions.

(1) Water as a base:
H_2?O(l)+H_2?S(g)?H₃?O⁺(aq)+HS⁻(aq)

(2) Water as an acid:
H_2?O(l) +NH₃?(aq)?OH⁻+NH₄⁺?

(3) Self ionization of water in which water simultaneously acts as acid and base.
2H₂?O→H

9.23. Cation exchange resins have large organic molecule with SO₃H group which are insoluble in water. Ion exchange resin (RSO₃H) is changed to RNa on treatment with NaCl. The resin exchange Na⁺ ions with Ca²⁺ and Mg²⁺ ions present in hard water and make it soft.
                                    2RNa (s) + M²⁺ (aq) ——> R₂M (s) + 2Na⁺ (aq)
where, M = Mg, Ca.
The resins can be regenerated by adding aqueous NaCl solution.

9.22. Temporary hardness of water is due to the presence of bicarbonates of calcium and magnesium in water i.e., Ca (HCO₃)₂ and Mg (HCO₃) in water. Permanent hardness of water is due to the presence of soluble chlorides and sulphates of calcium and magnesium i.e., CaCl₂, CaSO₄, MgCl₂ and MgSO₄.