Fundamental Chemistry and Hydraulics - Mathematics and Statistics for the Environment - page 344

Solution: Normally, for a conversion from gallons to pounds, we would use the factor 8.34 lb/gal (the
density of water) if the specific gravity of the substance is between 0.98 and 1.02. However, in this
instance the substance has a specific gravity outside this range, so the 8.34 factor must be adjusted.

1. Multiply 8.34 lb/gal by the specific gravity to obtain the adjusted factor:

8.34 lb/gal × 0.94 = 7.84 lb/gal (rounded)

2. Then convert 1455 gal to pounds using the corrected factor:

1455 gal × 7.84 lb/gal = 11,407 lb (rounded)

■ EXAMPLE 14. 3
Problem: The specific gravity of a liquid substance is 0.96 at 64°F. What is the weight of 1 gal of
the substance?

Solution:

Weight = Specific gravity × weight of water = 0.96 × 8.34 lb/gal = 8.01 lb

■ EXAMPLE 14.4
Problem: A liquid has a specific gravity of 1.15. How many pounds is 66 gal of the liquid?

Solution:

Weight = 66 gal × 8.34 lb/gal × 1.15 = 633 lb

■ EXAMPLE 14.5
Problem: If a solid in water has a specific gravity of 1.30, what percent heavier is it than water?

Solution:

(Specificgravity of solid) − (specificgravity of water)

Specificgravity of water

Percentheavier = × 100

13010
10

. − ×= .

= 100 30 %

.

14.1.2 W ater C hemistry F undamentals
Whenever we add a chemical substance to another chemical substance, such as adding sugar to tea
or hypochlorite to water to make it safe to drink, we are performing the work of chemists. We are
working as “chemists” because we are working with chemical substances, and how they react is
important to us. Environmental practitioners involved with water treatment operations, for example,
may be required to determine the amount of chemicals or chemical compounds to add (dosing) to
various unit processes. Table 14.2 lists some of the chemicals and their common applications in
water treatment operations.

14.1.2.1 Water Molecules
Just about everyone knows that water is a chemical compound of two simple and abundant elements:
H 2 O. Yet, scientists continue to argue the merits of rival theories on the structure of water. The fact
is that we still know little about water; for example, we don't know how water works. The reality is
that water is very complex and has many unique properties that are essential to life and determine