Any treatment system that uses hypochlorination for their disinfection process has to be able to solve for their strength of solution.** **Strength of solution (SOS) compares the weight of a chemical you add to water as compared to the weight of the water that you put the chemical in, plus the weight of the chemical. Though there are a couple of different formulas that can be used for SOS, we will be covering SOS = weight of chemical/ weight of solution.

When solving for SOS, you must have the weight of your water and chemical in the same unit, which needs to be in pounds. Also, remember when doing this problem that most situations want an answer in percentage form. After solving the equation, simply multiply the answer you get by 100 to convert any number to a percent.

Let’s work out an example:

You are adding 12 pounds of lime to 100 gallons of water. What is the strength of solution?

SOS = wt. of chemical

Wt. of solution

You have to remember that both your numbers have to be in the same units. Also, the weight of the solution is the weight of water plus the chemical. When converting pounds of water to gallons, we multiply 8.34.

SOS = 12 pounds

12 pounds + (100 x 8.34)

SOS= 12 pounds

12 pounds + 834 pounds

SOS= 12

846

In the last step if the answer is or needs to be in percent form, you must convert your decimal to a percent by multiplying by 100.

SOS = .014 x 100

SOS= 1.4 percent

To try out a practice problem, check out Test Your Knowledge – Strength of Solution.

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