for university students

1. Dr.S.Z.Bootwala
Wilson College

3.  Water is easy available, neutral, odourless, non – toxic
 Can be handled safely
 has wide range of liquid state (0 – 100℃)  is liquid at
ordinary temperature,
 high dielectric constant (78.5)  is capable of reducing
forces of electrostatic attraction binding the charged
ions in electrolytes in the solid state. thus, salts and
other electrolytes get dissociated into ions when they
dissolve in water and the solution conducts electricity.
 high dipole moment, heat of vapourisation
 ability to dissolve a large number of substances.
water is not always a suitable solvent
Χ Some reagents may react with H2O (e.g.
the alkali metals)
Χ non-polar molecules are insoluble in
water.

4. NON-AQUEOUS SOLVENTS
 The solvents other than water which are used for carrying
out chemical reactions are called non-aqueous solvents.
NON-
AQUEOUS
SOLVENTS
Organic non-
aqueous
solvents
Benzene, carbon
tetrachloride,
acetone, ether etc
Inorganic
non-aqueous
solvents
Liquid ammonia, sulphuric
acid, liquid HF, liquid sulphur
dioxide etc

5. Importance of non-aqueous solvents.
water as solvent has few limitations.
 It cannot be used as solvent during reactions involving
acids stronger than H3O+ and bases stronger than OH-.
 During the use of strong reducing agents, water
cannot be used, as strong reducing agent would react
with water.

6. Importance of non-aqueous solvents.
In many cases, non-aqueous solvents can serve as better
solvent than water.
 By changing the solvent medium, the product from
given set of reaction can be completely changed. This
indicates the influence of solvent on chemical
reaction.
 Reaction in water :
2AgNO3 + BaCl2 → 2AgCl  + Ba(NO3)2
 Reaction in Ammonia:
2AgCl + Ba(NO3)2 → BaCl2 + 2AgNO3

7. Importance of non-aqueous solvents.
 It is possible to precipitate KCl in a non-aqueous
solvent (liq.NH3), but it is impossible to precipitate
KCl in an aqueous medium.
 Non-aqueous solvent is used to improve the strength
of weak acid. For example CH3COOH behaves like a
weak acid in water medium but the same acid behaves
like a strong acid in liquid NH3 medium.
 Relative strength of various acids like HClO4, HI, HCl,
HBr and HNO3 can be determined in non-aqueous
solvent, NH3, but not in aqueous medium.

8. Physical Properties of Solvent
A )Melting & Boiling Point (Liq. Range)
 Water has excellent liquid range( 0 to 100℃) at
ordinary temp and pressure. Acids can also act as
solvent at ordinary temp while liq.NH3 (-77.7 to -
33.4℃) and liq. SO2(-75.5 to -10.2℃) can act as solvent
only at low temp.

9. Physical Properties of Solvent
B) Heat of Fusion & Heat of vaporization:
 A high heat of vaporization of liquid indicates that the
intermolecular forces in it are strong.
∆Hvap/Tboiling pt. = Trouton Constant
 The ratio of the heat of vaporization expressed in joules to
the boiling point(K) is a constant known as Trouton
Constant.
 High value of Trouton constant indicates associated
molecules.
 Molar heat of fusion for water (6.0kJ/mol) and
ammonia(5.65kJ/mol) are almost same, this means the
forces which hold molecules together in H2O and NH3 are
of same magnitude.

10. Physical Properties of Solvent
C)Dielectric Constant:
This property measures the polar nature of
solvent and helps to estimate solubility of polar
and non polar substances in the solvent.
In solvent of high dielectric constants, the ionic
substances will dissolve readily. With decrease in
dielectric constant, the solubility of ionic
compounds decreases.
NH3 and SO2 with small value of dielectric
constant values show decreased tendency to
dissolve ionic compounds.

11. Physical Properties of Solvent
D)Dipole Moment:
 Greater is the Polarity between bonds in the molecules
,larger is the dipole moment.
 And with increase in dipole moment ,tendency to
dissolve ionic substance increases.
E)Viscosity:
 It is the measure of fluidity of the solvent.
 In solvents of low viscosity the operations such as
precipitation, crystallization,filtration etc can be easily
carried out without any difficulty.