Chapter 9 - Solutions, Acids & Bases
Solutions
A solution is a mixture of materials, one of which is usually a
fluid. A fluid is a material that flows, such as a liquid or a gas. The
fluid of a solution is usually the solvent
. The material other than
the solvent is the
solute. We say that we dissolve the solute into
the solvent.

Some solutions are so common to us that we give them a unique
name. A solution of water and sugar is called syrup. A solution of
sodium chloride (common table salt) in water is called brine. A
sterilized specific concentration (0.15 molar) of sodium chloride in
water is called saline. A solution of carbon dioxide in water is
called seltzer, and a solution of ammonia gas in water is called
ammonia water.

A solution is said to be
dilute if there is less of the solute. The
process of adding more solvent to a solution or removing some of
the solute is called
diluting. A solution is said to be
concentrated if it has more solute. The process of adding more
solute or removing some of the solvent is called concentrating.
The concentration of a solution is some measurement of how
much solute there is in the solution
.

Solids are difficult to consider as solvents because there is a lack
of motion of the particles of a solid relative to each other. There
are, however, some good reasons to view some mixtures of these
types as solutions. The molecules of a gas do knock against each
other, and the motion of a gas can assist in changing material
from a liquid or solid state.

True solutions with liquid solvents have the following properties:
                        PROPERTIES OF SOLUTIONS

  • The particles of solute are the size of individual small molecules or
    individual small ions. One nanometer is about the maximum diameter for a
    solute particle.
In solutions individual
molecules of the solute
are mixed evenly into
the molecules of the
solvent.
Solubility
can dissolve in a certain quantity of solvent or quantity of
solution at a specified temperature.

The main factors that have an effect on solubility are:

The nature of the solute and solvent  --  While only 1
gram of lead (II) chloride can be dissolved in 100 grams
of water at room temperature, 200 grams of zinc chloride
can be dissolved.  The great difference in the solubilities
of the of these two substances is the the result of
differences in their natures.

Temperature  --  Generally, an increase in the
temperature of the solution increases the solubility of a
solid solute.  A few solid solutes, however, are less
soluble in warmer solutions.   For all gases, solubility
decreases as the temperature of the solution rises.

Pressure  --  For solids and liquid solutes, changes in
pressure have practically no effect on solubility.  For
gaseous solutes, an increase in pressure increases
solubility and a decrease in pressure decreases
solubility.  (When  the cap on a bottle of soda pop is
removed, pressure is released, and the gaseous solute
bubbles out of solution.  This escape of a gas from
solution is called effervescence.)  
Solubility of different
substances in relation to
temperature.
Concentration
  • The mixture does not separate on standing. In a gravity environment the solution will not come apart due to any difference
    through the filter.
  • Once it is completely mixed, the mixture is homogeneous. If you take a sample of the solution from any point in the
    solution, the proportions of the materials will be the same.
  • The mixture appears clear rather than cloudy. It may have some color to it, but it seems to be transparent otherwise. The
    mixture shows no Tyndall effect. Light is not scattered by the solution. If you shine a light into the solution, the pathway of
    the light through the solution is not revealed to an observer out of the pathway.
  • The solute is completely dissolved into the solvent up to a point characteristic of the solvent, solute, and temperature. At a
    saturation point the solvent no longer can dissolve any more of the solute. If there is a saturation point, the point is distinct
    and characteristic of the type of materials and temperature of the solution.
  • The solution of an ionic material into water will result in an electrolyte solution. The ions of solute will separate in water to
    permit the solution to carry an electric current.
  • The solution shows an increase in boiling point as the amount of solute is increased.
  • The solution shows a decrease in melting point as the amount of solute is increased.