Course 6: Introduction to Free Chlorine
- Lesson 1 – Free Chlorine for Water Disinfection (2:05)
- Lesson 2 – Measuring Free Chlorine (2:33)
- Lesson 3 – pH and Free Chlorine (5:37)
- Lesson 4 – Parts of a Free Chlorine Measurement Signal (5:47)
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Lesson 3 – pH and Free Chlorine (5:37)
Watch the video to learn about the pH-dependence of a free chlorine measurement.
> Hypochlorous acid dissociates into the hypochlorite ion (OCl-) and a proton (H+), which is pH-dependent:
HOCl(aq) ↔ OCl-(aq) + H+(aq)
> As pH increases, the amount of HOCl present decreases, and OCl- increases.
> Free chlorine is the sum of hypochlorous acid, hypochlorite ion, and molecular chlorine (Cl2):
Free chlorine = HOCl + OCl- + Cl2
> The Zirkon DIS sensor measures only HOCl, and a pH measurement is used to quantify OCl- concentration. Molecular chlorine is only present at pH < 4.