and alkaline media.
Reactions involving oxidizing actions are:
Reactions involving reduction actions are:
Q: 26. What is meant by ‘demineralised’ water and how can it be obtained?
Demineralised water is obtained by passing water successively through a cation exchange (in the from) and an anion exchange (in the from) resin.
During the cation exchange process, exchanges for , and other cations present in water.
In the anion, exchange process, exchanges for anions such as etc. present in water.
ions liberated in reaction (2) neutralize ions liberated in reaction (1), thereby forming water.
Q: 27. Is demineralised or distilled water useful for drinking purposes? If not, how can it be made useful?
Water is an important part of life. It contains several dissolved nutrients that are required by human beings, plants, and animals for survival. Demineralised water is free of all soluble minerals. Hence, it is not fir for drinking.
It can be made useful only after the addition of desired minerals in specific amounts, which are important for growth.
Q: 28. Describe the usefulness of water in biosphere and biological systems.
Water is essential for all forms of life. It constitutes around of the human body and 95% of plants. Water plays an important role in the biosphere owing to its high specific heat, thermal conductivity, surface tension, dipole moment, and dielectric constant. The high heat of vaporization and heat of capacity of water helps in moderating the climate and body temperature of all living beings.
It acts as a carrier of various nutrients required by plants and animals for various metabolic reactions.
Q: 29. What properties of water make it useful as a solvent? What types of compound can it (i) dissolve, and (ii) hydrolyse?
A high value of dielectric constants and dipole moment make water a universal solvent.
Water is able to dissolve most ionic and covalent compounds. Ionic compounds dissolve in water because of the ion-dipole interaction, whereas covalent compounds form hydrogen bonding and dissolve in water.
Water can hydrolyze metallic and non-metallic oxides, hydrides, carbides, phosphides, nitrides and various other salts. During hydrolysis, and ions of water interact with the reacting molecule.
Some reactions are:
Q: 31. What is the difference between the terms ‘hydrolysis’ and ‘hydration’?
Hydrolysis is defined as a chemical reaction in which hydrogen and hydroxide ions ( and ions) of water molecule react with a compound to form products. For example:
Hydration is defined as the addition of one or more water molecules to ions or molecules to form hydrated compounds. For example:
Q: 32. How can saline hydrides remove traces of water from organic compounds?
Saline hydrides are ionic in nature. They react with water to form a metal hydroxide along with the liberation of hydrogen gas. The reaction of saline hydrides with water can be represented as:
(Where, A = Na, Ca, …)
When added to an organic solvent, they react with water present in it. Hydrogen escapes into the atmosphere leaving behind the metallic hydroxide. The dry organic solvent distills over.