Solutions
A solution is a homogeneous mixture composed of two or more
substances. In such a mixture, a solute is dissolved in another substance,
known as a solvent. The solvent does the dissolving.
Properties of Solutions
 Reqular distribution of atoms (or molecules or ions) solutes
in solvent.
 Ease of recovery of solute or solvent in solution
Classification of Solutions:
Solutions can be classified into particles size and solute
concentration.
 Solute particles size
true solution
A true solution is a homogeneous solution in which the solute particles have
diameters less than 10-7cm. i.e., the solute particles are of molecular dimensions.
The particles are invisible even under powerful microscopes.
For example, sodium chloride in water is a true solution. Most ionic compounds
form true solutions in water. Organic compounds like sugar and urea also form
true solutions in water.
Suspensions
A suspension is a heterogeneous mixture in which one or more components
have a particle size greater than 10-5cm. Very often these particles are visible to
the naked eye.
For example, sand in water, sodium chloride in benzene, turmeric in water etc.
Colloids
A colloid is a solution in which the particle size ranges between 10 -7 and 10-5 cm.
For example, milk, blood, honey, smoke, ink, gum, starch solution etc.
Difference between true solutions, suspensions
and colloids
Property
True solutions
Colloidal solutions
Particle size
Between 10 - 5 and
Less than 10 - 7 cm
10 - 7 cm
Greater
than
cm
Visibility of
particles
Invisible to naked
eye not visible
under powerful
microscope
Easily visible
Invisible to naked
eye. Visible under
powerful microscope
Suspensions
10 - 5
Sedimentation of
Settle down under
Do not settle down
particles
high centrifugation
Settle down due
to gravity
Filtration
through filter
paper
Residue is
formed
No residue is
formed
No residue is formed
 Solute Concentration
1. Saturated solutions have the maximum amount of
solute dissolved in them. No more solute can be made to
dissolve.
2. Unsaturated solutions have less than the maximum
amount of solute dissolved in them. This means that more
solute could be added to the solution and the additional
solute would still dissolve.
3. Supersaturated solutions have more than the maximum
amount of solute dissolved in them. This is not normally
possible. Not all substances will form supersaturated
solutions. If a crystal of the solute is added to a
supersaturated solution, precipitation of all of the extra
solute will occur.
Definitions of Acids and Bases
 Arrhenius Acids and Bases
The Arrhenius definition of acids and bases is one of the oldest. An
Arrhenius acid is a substance that when added to water increases the
concentration of H1+ ions present. The chemical formulas of Arrhenius acids
are written with the acidic hydrogens first. An Arrhenius base is a
substance that when added to water increases the concentration of OH1- ions
present. HCl is an example of an Arrhenius acid and NaOH is an example of
an Arrhenius base.
 Bronsted-Lowry Definition of Acids and Bases
We will use the Bronsted-Lowry definitions for acids and bases:
Acids are species that donate a proton (H+).
and
bases are species that accept a proton.
Acid example:
HNO3 (aq) + H2O
NO3-(aq) + H3O+(aq)
Keq = a very large number
In this example, HNO3 is an acid and H2O is acting as a base.
NO3- is called the conjugate base of the acid HNO3, and H3O+ is the
conjugate acid of the base H2O.
Base example:
NH3 (aq) + H2O
NH4+(aq) + OH-(aq)
K = 1.8x10-5
In this example, NH3 is a base and H2O is acting as an acid. NH4+ is the
conjugate acid of the base NH3, and OH- is the conjugate base of the acid
H2O.
A compound that can act as either an acid or a base, such as the H2O in the
above examples, is called amphiprotic.