The previous three chapters were concerned with elements, compounds, and their
chemical reactions. Elements and compounds are pure substances, materials with
a definite, fixed composition that is the same throughout. Mixtures, on the
other hand, have a composition that may vary from one sample to the next. A
mixture contains the particles of one substance physically dispersed throughout
the particles of another substance. These particles can be any size, from the
size of rock particles in a gravel mixture down to the smallest size possible--particles
the size of ions or molecules. The size of the particles gives a mixture its
appearance. When the particles are relatively large and visible to the eye,
a mixture appears to be heterogeneous. Thus, a pile of gravel appears to be
a heterogeneous mixture. At the other end of the size scale, a uniform mixture
of ion- or molecule-sized particles appears to be homogeneous, or the same throughout.
Such homogeneous mixtures are called solutions. This chapter is concerned with
solutions, those involving water in particular. Many common liquids are solutions. Solutions are commonly used in everyday
household activities, as well as in the chemistry laboratory. The household
activities of cooking, cleaning, and painting all involve solutions that will
be considered in this chapter. Detergents, cleaners, and drain openers all function
because a solution is a medium for rapid chemical change. Solids react slowly,
if at all, because they have limited contact only at their immediate surfaces.
Thus, solutions are commonly used to speed reactions. The water you drink is
also a solution (Figure 13.1). Hard water results in certain reactions that
occur between soap and the water solution. This chapter considers hard water
and how it is softened, in addition to acids, bases, the pH scale, and many
common solutions used in everyday activities. |
2002 McGraw-Hill Higher Education