Nearly every chemical reaction takes place in homogeneous mixtures called
solutions.
Therefore, we must understand the properties of solutions before we can
even begin to understand
those reactions. Perhaps the most salient characteristic of a solution is its
concentration--how much
solute is dissolved in what amount of solvent. Several different
units of concentration like
mass percent, mole fraction, molarity, normality, and
molality have been
developed for use in different situations.
Solution Composition explains the
definitions and uses of those units and why it is necessary to have so many
different units of
concentration.
After we have discussed the units of concentration, we will explore the
questions of why solutions
form at all and what factors affect the solubility of solutes in
different solvents. As we shall see,
like dissolves like. Non-polar solvents dissolve non-polar solutes
better than polar
solvents and polar solvents dissolve polar solutes better than
non-polar solvents. Raising the
temperature of a solution will increase the solubility of most solid
solutes. Likewise, according to
Henry's law, increasing the pressure above a solution will increase the
solubility of most
gaseous solutes.
There are several other properties of solutions, besides concentration and
solubility, called
colligative properties, that depend only on the number of solute
particles, not on their identities.
The colligative properties that we will study are vapor pressure lowering,
freezing point depression,
boiling point elevation, and osmotic pressure. Each of those properties is
discussed in detail in
Colligative Properties.
