How many pounds of a chemical are needed to dose 200,000 gallons at a rate of 3 mg/L?

To determine how many pounds of a chemical are needed to dose 200,000 gallons of water at a rate of 3 mg/L, you'll need to start by converting the volume of water from gallons to liters. There are approximately 3.785 liters in a gallon, so:

200,000 gallons × 3.785 liters/gallon = 757,000 liters of water.

Next, since the dosage is given in mg/L, the total mass of the chemical can be calculated using the formula:

Mass (mg) = Concentration (mg/L) × Volume (L)

This means:

Mass (mg) = 3 mg/L × 757,000 L = 2,271,000 mg.

Now, convert milligrams to pounds. There are 453,592.37 milligrams in a pound, so:

Mass (pounds) = 2,271,000 mg ÷ 453,592.37 mg/pound ≈ 5 pounds.

Thus, the result indicates that you would need approximately 5 pounds of the chemical to achieve the desired dose of 3 mg/L in 200,000 gallons of water. This choice aligns with the calculations above, confirming why it is the correct answer.