North Carolina Surface Water Math Practice Test

To determine how many pounds of 7% bleach are needed to reach a concentration of 2 parts per million (ppm) in 6 million gallons, we need to follow a series of calculations.

First, convert the volume of water from gallons to pounds, since 1 gallon of water weighs approximately 8.34 pounds. Therefore, for 6 million gallons:

6,000,000 gallons × 8.34 pounds/gallon = 50,040,000 pounds.

Next, to obtain a concentration of 2 ppm in this total weight of water, we calculate the amount of bleach needed. The formula for ppm is:

ppm = (mass of solute / mass of solution) × 1,000,000.

Rearranging this formula to find the mass of the solute (bleach in this case):

mass of solute = ppm × mass of solution / 1,000,000.

Plugging in the numbers:

mass of solute = 2 ppm × 50,040,000 pounds / 1,000,000 = 100.08 pounds.

This means we need approximately 100.08 pounds of bleach to achieve the desired concentration. However, since we are using a 7%