Science of Water : Concepts and Applications

Water Treatment Calculations 395
Calculate the gpd hypochlorite solution required:
180 lbday
8.34 lbgal 21.6 gpd hypochlorite
CALCULATING PERCENT STRENGTH OF SOLUTIONS
If a teaspoon of salt is dropped into a glass of water it gradually disappears. The salt dissolves in
the water. A microscopic examination of the water would not show the salt. Only examination at the
molecular level, which is not easily done, would show salt and water molecules intimately mixed.
If we taste the liquid, of course, we would know that the salt is there, and we could recover the salt
by evaporating the water. In a solution, the molecules of the salt, the solute, are homogeneously
dispersed among the molecules of water, the solvent. This mixture of salt and water is homogenous
on a molecular level. Such a homogenous mixture is called a solution. The composition of a solution
can be varied within certain limits.
There are three common states of matter—gas, liquid, and solid. In this discussion, of course, we are
only concerned, at the moment, with solid (calcium hypochlorite) and liquid (sodium hypochlorite).
CALCULATING PERCENT STRENGTH USING DRY HYPOCHLORITE
In calculating the percent strength of a chlorine solution, we use Equation 10.93.
(hypochlorite, lb)(% available chlorine100) % Cl strength
100 (10.93)
Water, lb (hypochlorite, lb)(% available chlorine100) Example 10.119
Problem:
If a total of 72 oz of calcium hypochlorite (65% available chlorine) are added to 15 gal of water, what is
the percent chlorine strength (by weight) of the solution?
Solution:
Convert the ounces of hypochlorite into pounds of hypochlorite:
72 oz
4.5 lb chemical
16 oz/lb
(hypochlorite, lb)(% available chlorine100) % Cl strength
100
water, lb (hypochlorite, lb)(% available chlorine100) (4.5 lb)(0.65)
100
(15 gal)(8.34 lbgal) (4
lb)(0.65)
2.9 lb
100
125.1 lb 2.9 lb
(2.9)(100)
126
2.3 chlorine strength