Fundamental Chemistry and Hydraulics - Mathematics and Statistics for the Environment - page 345

TABLE 14.2
Chemicals and Chemical Compounds Used in Water Treatment

Name Common Application Name Common Application

Activated carbon Taste and odor control Aluminum sulfate Coagulation

Ammonia Chloramine disinfection Ammonium sulfate Coagulation

Calcium hydroxide Softening Calcium hypochlorite Disinfection

Calcium oxide Softening Carbon dioxide Recarbonation

Copper sulfate Algae control Ferric chloride Coagulation

Ferric sulfate Coagulation Magnesium hydroxide Deluoridation

Oxygen Aeration Potassium permanganate Oxidation

Sodium aluminate Coagulation Sodium bicarbonate pH adjustment

Sodium carbonate Softening Sodium chloride Ion exchanger regeneration

Sodium fluoride Fluoridation Sodium fluosilicate Fluoridation

Sodium hexametaphosphate Corrosion control Sodium hydroxide pH adjustment

Sodium hypochlorite Disinfection Sodium silicate Coagulation aid

Sodium thiosulfate Dechlorination Sulfur dioxide Dechlorination

Sulfuric acid pH adjustment

its environmental chemical behavior. In a water molecule, the two hydrogen atoms always come
to rest at an angle of approximately 105° from each other. The hydrogens tend to be positively
charged and the oxygen tends to be negatively charged. This arrangement gives the water molecule
an electrical polarity; that is, one end is positively charged and one end is negatively charged. This
105° relationship makes water lopsided, peculiar, and eccentric; it breaks all the rules (Figure 14.1).
In the laboratory, pure water contains no impurities, but in nature water contains a lot of materi-
als besides water. This is an important consideration for the environmental professional tasked
with maintaining the purest or cleanest water possible. Water is often called the universal solvent ,
a fitting description when you consider that, given enough time, water will dissolve anything and
everything on Earth.

14.1.2.2 Water Solutions
A solution is a condition in which one or more substances are uniformly and evenly mixed or dis-
solved. In other words, a solution is a homogeneous mixture of two or more substances. Solutions
can be solids, liquids, or gases, such as drinking water, seawater, air, etc. Here, we focus primarily
on liquid solutions. A solution has two components: a solvent and a solute (see Figure 14.2). The
solvent is the component that does the dissolving. Typically, the solvent is the species present in the
greater quantity. The solute is the component that is dissolved. When water dissolves substances, it
creates solutions with many impurities. Generally, a solution is transparent and not cloudy. Because

H +

O -

H +

FIGURE 14.1 A molecule of water.