Chapter 9 Hydrogen Solutions
Question - 21 : - Describe the structure of common form of ice.
Answer - 21 : - Ice crystallizes in the normal hexagonal form. However, at very low temperatures it condenses in cubic form. In the normal hexagonal ice each oxygen atom is tetrahedrally surrounded by four other hydrogen atoms.
Question - 22 : - What causes the temporary and permanent hardness of water?
Answer - 22 : -
Temporary hardness ofwater is due to the presence of bicarbonates of calcium and magnesium in wateri.e., Ca(HCO3)2 and Mg(HCO3) in water. Permanent hardness of water is due tothe presence of soluble chlorides and sulphates of calcium and magnesium i.e.,CaCl2, CaS04, MgCl2 and MgS04.
Question - 23 : - Discuss the principle and method of softening of hard water by synthetic ion-exchange resins.
Answer - 23 : -
Cation exchange resinshave large organic molecule with S03H group which are insoluble in water. Ion exchangeresin (RS03H) is changed to RNa on treatment with NaCl. Theresin 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 aqueousNaCl solution.
Question - 24 : - Write chemical reaction to show the amphoteric nature of water.
Answer - 24 : - Water is amphoteric in nature because it acts as an acid
Question - 25 : - Write chemical reactions to justify that hydrogen peroxide can function as an oxidising as well as reducing agent.
Answer - 25 : -
As an oxidising agent
2Fe2+ (aq) + 2H+(aq) +H2O2(aq) ———–> 2Fe3+ (aq) + 2 H2O(l)
As a reducing agent
I2(s) + H2O2 (aq) + 2OH– (aq) ———> 2I– (aq) + 2 H2O(l) + O2(g)
Question - 26 : - What is meant by ‘demineralised water’ and how can it be obtained?
Answer - 26 : -
Demineralised water isfree from all soluble mineral salts which is obtained by passing watersuccessively through a cation exchange (in the form of H+) and an anion exchange in the form of OH– resins.
H+ exchanges forNa+, Ca2+,Mg2+ and other cations presentin water. This process results in release of proton which makes the wateracidic.
OH– exchanges, for anions like Cl–, HCO3–,SO42-etc.
OH– ions thus liberatedneutralize the H+ ions set freein the cation exchange process. H+(aq)+ OH–(aq) ——-> H2O(l)
Question - 27 : - Is demineralised or distilled water useful for drinking purposes? If not, how can it be made useful ?
Answer - 27 : - No, demineralised water is not fit for drinking purposes. It can be made useful by adding required amount of ions which are useful for our body.
Question - 28 : - Describe the usefulness of water in biosphere and biological systems.
Answer - 28 : -
(i) Major part of allliving system is made of water.
(ii) It constitutes about 65 – 70% of body weightsof animals and plants.
(iii) Some properties of water like high specificheat, thermal conductivity, surface tension, high polarity allow water to playa major role in biosphere.
(iv) Because of high heat of vaporisation it isresponsible ro regulate temperature of living beings.
(v) It is an excellent fluid for thetransportation of minerals and nutrients in plants.
(vi) It is also required for photosynthesis inplants.
Question - 29 : - What properties of water make it useful as a solvent? What types of compound can it (i) dissolve (ii) hydrolyse?
Answer - 29 : -
Water is highly polar in nature thats why it has high dielectric constant and high dipole moment. Because of these properties, water is a universal solvent.
It can hydrolyse many oxides metallic or non-metallic, hydrides, carbides, nitrides etc.
Question - 30 : - Knowing the properties of H2O and D2O,do you think D2O canbe used for drinking purpose.
Answer - 30 : - No, D2O is injurious to human beings, plants and animals.