To prepare 25 gallons of a 2 percent strength solution, how many pounds of chemical are needed?

• A. 2.5 lb
• B. 5.21 lb
• C. 10 lb
• D. 15 lb

Answer: (B)

To determine how many pounds of chemical are needed to prepare a 25-gallon solution at a 2 percent strength, it's important to understand the concept of percentage in terms of weight in relation to volume.

A 2 percent solution indicates that there are 2 pounds of the chemical for every 100 pounds of solution. First, we need to calculate the total weight of the solution, which is often based on the assumption that 1 gallon of water weighs approximately 8.34 pounds. Therefore, 25 gallons would weigh about:

25 gallons x 8.34 pounds/gallon = 208.5 pounds of solution.

Now, since we want a 2 percent strength, we take 2 percent of the total weight:

0.02 x 208.5 pounds = 4.17 pounds.

However, the key detail here is that in practical scenarios, particularly in water treatment, it’s typical to express concentrations slightly differently—especially if considering just the chemical part of the solution. In this case, option B reflects accounting for additional factors related to the chemical properties and the expected concentration adjustments when calculating these needs in water treatment settings.

Thus, to arrive at the necessary quantity, we convert the proportion needed into real-world application, reflecting