Final answer:
The chlorine residual at the point of consumption includes both free and combined forms of chlorine, measured to ensure water safety. A titration method is used for determining the total chlorine residual and maintaining proper disinfection levels is crucial for public health, highlighted by regulations in pool water chlorination.
Step-by-step explanation:
The chlorine residual at the point of consumption refers to the concentration of chlorine remaining in the water after it has traveled through the distribution system to the consumer's tap. The total chlorine residual is a measure of this concentration and includes both free chlorine residual, such as Cl2, HOCl, and OCl⁻, and combined chlorine residual, which consists of species like NH₂Cl, NHCl2, and NC13. These chlorinated compounds serve to maintain water quality by ensuring that harmful pathogens are destroyed. A common method to determine the total chlorine residual is by using the titration method, where an oxidizing reaction with iodide converts chlorine to I3⁻, which is then quantified using a titrant such as Na₂S₂O3, with starch as an indicator to determine the endpoint of the titration.The goal of adding chlorine to the water supply is not only to disinfect the water but also to maintain a residual chlorine level to ensure continuous disinfection as the water makes its way to consumers. It is essential for public health to monitor the chlorine residual as it indicates the effectiveness of water treatment. Pool water, as an example, should be chlorinated to a maximum level of 3.0 ppm to ensure safety against contaminants, and the amount of chlorine added must be calculated based on the volume of the pool and desired chlorine concentration.