Ontario Operator-in-Training (OIT) Practice Exam

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Study for the Ontario Operator-in-Training Exam. Review flashcards and multiple choice questions, each with hints and explanations. Prepare for your certification!

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If the chlorine dosage of a town's water source is 4.0 mg/L and the chlorine demand for the water is 3.7 mg/L, what is the chlorine residual?

0.1 mg/L
0.3 mg/L
0.5 mg/L
1.0 mg/L

The correct answer is: 0.3 mg/L

To determine the chlorine residual, you need to subtract the chlorine demand from the chlorine dosage. The chlorine dosage represents the total amount of chlorine added to the water, while the chlorine demand indicates how much of that chlorine is required to react with substances in the water. In this case, the chlorine dosage is 4.0 mg/L and the chlorine demand is 3.7 mg/L. By lining these values up in a subtraction equation: Chlorine Residual = Chlorine Dosage - Chlorine Demand Chlorine Residual = 4.0 mg/L - 3.7 mg/L Chlorine Residual = 0.3 mg/L Thus, the chlorine residual is 0.3 mg/L, which reflects the amount of chlorine that remains in the water after meeting the demand of the contaminants present in the water source. This residual chlorine is important as it ensures that disinfection continues beyond the treatment process. Understanding this calculation is crucial for water treatment operators, as adequate chlorine residual is necessary to assure ongoing disinfection as the water travels through the distribution system to consumers.