13
pH = −
×
 
  =
−
log
.
10
7
1 0 10
7
pH values of various water and wastewater, and discharge standards for treated
wastewater are shown in Fig. 1.7. The standards of 6–9 is usually practiced even
though standards of 6.5–8.5 are sometimes prescribed by some countries as it is not
practically possible to bring down the pH value to exactly 7.
Reaction between acid and base will result in salts. In other words, a salt is the
product of an acid–base reaction. A salt is an ionic compound having some cation
other than hydrogen as well as some anion other than hydroxide as well as oxide.
1.2.1 The Gas Laws
The gas laws are important to the environmental professionals as we live and breathe
in air that has direct impact on our health. The numerous chemical molecules within
the environment and our body interact as per natural phenomena explained by the
gas laws, briefly explained in subsequent sections.
1.2.1.1 Boyle’s Law
Boyle’s law states that the volume of an ideal gas is inversely proportional to its
pressure at a constant temperature (Fig. 1.8).
The law is written as:
1 kg
1 kg
1 kg
T = X
o C
T = X
o C
Fig. 1.8 Schematic depiction of Boyle’s law
1.2 General Chemistry