Georgia Drinking Water Laboratory Analyst Practice Test

The optimal pH range for determining free chlorine using the amperometric titration method is typically around 6.5 to 7.5. This range is important because it is near neutral pH, where free chlorine exists primarily as hypochlorous acid (HOCl), which is the most effective form of chlorine for disinfection and is also the form that amperometric titration methods measure most accurately.

At this pH, the response of the electrodes used in the amperometric titration is maximized, providing reliable and reproducible results. The electrodes are better at detecting the concentration of hypochlorous acid within this range, leading to more precise measurements. pH levels below or above this optimal range can affect the chemistry of chlorine, causing shifts between different species of chlorine (like hypochlorite ions) that may not produce a clear signal in the amperometric method. This could result in inaccurate readings of free chlorine levels, hence the preference for operating within the 6.5 to 7.5 pH range to ensure effective and accurate analysis.