General Properties of Aqueous Solutions
Aqueous medium (water medium) is a very powerful medium; most of the chemical
reactions and nearly all the biochemical reactions take place in this medium. It is
important to understand how different substances behave in solutions made with water.
Let us start with the definition of a solution and its components. A solution is a
homogeneous mixture of substances. Simple solutions have two components, one is a
dissolved substance and another one is a dissolving medium. The dissolved substance is
usually present in a smaller ratio (proportion) and termed as a solute. The dissolving
medium is usually present in a larger proportion and known as a solvent. The solvent is
a liquid and in aqueous solution it is a water. The solute can be either solid or liquid or a
gas.
Electrolytes and Non-electrolytes
All solutes dissolved in water can be classified as electrolytes or non-electrolytes. An
electrolyte is a substance that breaks up into ions when dissolved in water. Since it
breaks up into ions, it can conduct electricity. On the other hand, non-electrolyte is a
substance that does not break up into ions when dissolved in water. Among the
electrolytes, there are two kinds; (a) strong electrolyte and (b) weak electrolyte. The
strong electrolyte dissociates completely (100%) into ions in solution, where as, weak
electrolyte does not dissociate completely into ions in solution. The chemical reaction
for the dissociation of strong electrolyte is written with a single arrow going from
reactants to products like (think this is one-way street – traffic going in only direction),
NaCl(s) Æ Na+(aq) + Cl-(aq)
The chemical reaction for the dissociation of weak electrolyte is written with double
arrows going in opposite directions like (think this is two-way street – traffic going in
both directions),
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CH COOH(aq) CH COO (aq) H (aq)
−+
⎯⎯→+
←⎯⎯
Generally, ionic compounds are strong electrolytes. However, there are few acids and
bases are strong electrolytes. See the following table.
Strong Electrolytes Weak Electrolytes
Nonelectrolytes
Ionic compounds
HCl ( hydrochloric acid) CH3COOH (acetic acid) CH3OH (methyl alcohol)
HNO3 (nitric acid) HF (hydrofluoric acid) C2H5OH (ethyl alcohol)
HClO4(perchloric acid) HNO2 (nitrous acid) C6H12O6 (glucose)
H2SO4 (sulfuric acid) NH3(ammonia) C12H22O11 (sucrose/table sugar)
NaOH (sodium NH2-CO-NH2 (urea)
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