The relationship between ORP and residual chlorine
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Find the relationship between ORP and residual chlorine
There is no strict direct relationship between ORP and residual chlorine; although a high concentration of residual chlorine will also result in a high ORP value. The ORP value is also related to pH and the concentration of dissolved oxygen in water. The ORP value represents the combined effect of all oxidizing substances in water, whereas residual chlorine is merely an indication of the concentration of active chlorine.
We want to install an online ORP sensor in the chlorination tailwater tank, and hydrogen peroxide is being used to remove free chlorine; we are currently conducting comparative experiments to determine whether an excess of hydrogen peroxide causes the ORP reading to be negative, and whether the pH value measured with test strips is alkaline； I measured the ORP of pure water, and it showed 361 mV.
Hydrogen peroxide is also oxidizing, and its potential should also be within the positive range. The reaction of free chlorine with hydrogen peroxide does not mean that hydrogen peroxide will exhibit a negative potential; it can only be said that hydrogen peroxide is an oxidizing agent that is slightly less strong than free chlorine, and it is only in comparison to free chlorine that hydrogen peroxide shows reducibility. Additionally, there is also dissolved oxygen in pure water, and dissolved oxygen is an oxidizing agent as well.