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fee, , , , NON-AQUEOUS SOLVENTS, , —_— . 5, solvent. A solvent is defined as a substance which has the, “excellent solvent. On account of its high dielectric constant,, n ai binding the charged ions in electrolytes in the, ated into ions when they dissolve m water and the solutions conduct electricity Water has a long liqui, are °C) and hence is liquid at ordinary temperatures. ts ily avai lene, rae (0° 10 100 t My temperatures, It is most easily available and ¢, warifed. It is neutral, odourless, non-toxic and non-poisonous. ean, therefore, be handled, wl these characteristics, water serves as the most useful solvent,, i, , Power of dissolvin, , po 8 other substanves, Water, Wis capable ab, , of reducing forces of e, , t pa leetrostatio, solid state, Thus, salts and other ele, , clrolytes pet, , an be easily, ely, Due to, , Anempts have been made to find out some other common substances which could Serve as good solvents, tke water and could also have sizeable dielectric constants so that they could have high ionising capacities,, Liquid ammonia, liquid sulphur dioxide, anhydrous hydrogen fluoride, anhydrous sulphuric acid and liquid, nitrogen tetroxide are some such solvents., , Classification of Solvents. The various solvents are generally classified as follows :, , 1. Protonic and aprotic solvents. Solvents from which Protons (ie, H* ions) can be derived are called, prowonic solvents. Common examples are : HO, NH, HF, ete. Solvents from which protons cannot be ordinarily, cerved are called aprotic solvents. Examples are : CCL, CoH, acetonitrile, ete., , 2. Acid solvents, basic solvents and amphiprotic solvents. Solvents which have 3, give protons are called acid solvents, e.g., liquid hydrogen fluoride, sulphuric, which have strong affinity for protons are called basic solvents, e. @., liquid, Amphiprotic solvents are those which neither have a strong tendency to, Protons. Examples are : water, methy] alcohol, ethyl alcohol, ete., , 1 strong tendency to, acid and acetic acid. Solvents, ammonia, pyridine, hydrazine, ete,, gain nor a strong tendency to lose, , 3. Tonising and non-ionising solvents. Ionising solvents are those which are capable of undergoing auto, or self-ionisation, Examples are : water, ammonia, sulphur dioxide, ete. These solvents ionise as follows :, , H,O + H,O = H;0° + OH, NH; + NH; == NH,* + NH, SO, + SO, = SO% + SO;>, Solvents which do not ionise at all are non-ionising solvents. lonising solvents have high dielectric, , and are polar. Non-ionising solvents have low dielectric constants and are non-polar., , whi phatacterstc Pr operties of a Solvent. Some characteristic physical and chemical properties of a solvent, i . cack, ch govern Mts usefulness as a solvent are given below., , 1. Meltin, , . . ili ints of a solvent indicate the range of, oint a int. The melting and boiling points o|, , Mert ® point and boiling point. Th ig, , ints, , ‘ ssure. The melti piling, Fe Over which it can exist in the liquid state under atmospheric pressure, The mele et ig, Sl various solvents alongwith their critical temperatures and critical pressures are giver, , 275, , >

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afiv, , , , , , , , , , , , , ints and Critical Constants of Variguy Solveny,, oints, , , , , , , , i Boiling P, ST BAP. (°C) Critical, temperature (20), 300-0 2, , ae 100-0 zh, Sulphuric 2 oe we, Water “Het 05 ne, Ammonia ; oa w ts, Sulphur dioxide a., Hydrogen fluoride MD be, Dinitrogen tetroxide , , , , , Because of the above valu, and sulphur dioxide exist as &, , Jow temperatures., , a3i)8 by one mole of a substance, i ation. The heat absorbed, 2. Heats of i 4 Oued of fusion. Likewise, the heat absorbed by one m, fro Tigui reap state is called its molar heat of vaporisation. These constants, change from li, , to liquid state i, , sulphur dioxide and hydrogen, fluoride are given in Table 2., , The heats of fusion and, , Molar Heats of Fusion and Vaporisation of, , hile water exists as liquid at ordinary temperature, es " under these conditions. These gases, therefore,, ase:, , TABLE 2, , , , , 4nd Pressur. ., , amt 9 Gti "%, act ag 50M vent, z i, , 0 change 5 ces, ole of a sing, for Water, ats, , is, , Some Sotven ts, , , , , , vaporisation indicate the nature and, strength of forces with which the, , , , , , molecules of the solvent are held, together in the solid or the liquid, state. A high heat of vaporisation of, a liquid indicates that the, intermolecular forces in it are strong., A better idea of the intermolecular, , , , , , Solvents Molar heat of fusion | Molar heat of Vaporisateg, (kJ. mol-!) . at boiling point (4 uf}, , Water 6-02 40-65, Ammonia 5-65 23-34 |, Sulphur dioxide 7-40 24-93 |, Hydrogen fluoride 4-58 30-28 |, , , , , , , , for, the heat of vaporisation expressed in, This constant is about 90 J K-! mol!, between them. A higher y., which undergo associatio, alcohols are al] associated, It is fr, indicates, , liquids,, evident, that the 3, sulphur dioxide jg, , ces is obtained by dividing the heat of va, , lecul, comparat, , porisation by t, , joules to the boiling po, -! for normal |, alue of the constant i, , m are polar. The co;, , , , iquids. Such liquids, indicates association, , he boiling point. For normal liquids, the ratio of, , int (K) is, , TABLE 3, , . Solvents, Dipole Moments and Dielectric Constants of Some, , a constant known as Trouton constant, have single molecules without any bots, of molecules. The molecules of liguis, mmon solvents like water, ammonia, hydrogen fluoride and, , Tom Table 2 that heats of fusi i early the same. Tté, sins ih hold molecules together in ance od ammonia are very nearly thes, , €s together in water and ammonia are of the same mae low, vely high while that of hydrogen fluoride is comparative?, , , , , , , , Dipole Moment, (Debye Units), , of, Dielectric Consta!, , , , , , , , 2 Molecy] js, force boing HE melee iow =, 3. Die! tric, ap ombie force F ven ote’ euioat, uy 'S given by th express, : cha ca Where gy and 1 ate Water, {Wo ions and € is the dielectrign ei ie rhe, A high Value of ¢ Ndicate: th aan ic i, , , , initropen tetroxide, , 1°85, 1-47, 1-61, 1-90, , ide, , , , , , , , 785 (25°C), 22-0 380), 174 (20%), 33-6 (0°O), 2-42 0°O)