Our water treatment facility used Chlorine Dioxide to disinfect the produced drinking water. The analysis results indicate concentrations of 0.2 mg/l of chlorine dioxide at the source. Can we analys residual chlorine in the distribution network? We dont have water quality standards for chlorine dioxide, only residual chlorine. Can I calculate the concentration of chlorine in the water from the concentration of chlorine dioxide?


1 Answer 1


Some chemistry, first add H2O2 and NaOH:

$\ce{2 ClO2 + H2O2 + 2 NaOH -> 2 NaClO2 + O2 (g) + 2 H2O }$

Source: https://chemiday.com/en/reaction/3-1-0-1114

Continue adding H2O2, as:

$\ce{2 NaClO2 + 2 H2O2 -> 2 NaClO + 2 O2 (g) + 2 H2O }$

$\ce{2 NaClO + 2 H2O2 -> 2 NaCl + 2 O2 (g) + 2 H2O }$

which implies a net reaction of:

$\ce{2 ClO2 + 5 H2O2 + 2 NaOH -> 2 NaCl + 5 O2 (g) + 6 H2O }$

So, slowly add H2O2 until the bubbling ceases. Collect the volume of oxygen and convert to moles. Divide by 2.5 to determine moles of ClO2 and your chlorine therefrom.

Here is a related reference, Titrimetric and photometric methods for determination of hypochlorite in commercial bleaches, which cites the use of hydrogen peroxide and acidic permanganate.

  • 1
    $\begingroup$ Please have a look at Is ChemiDay a reliable enough source (for inorganic reactions) to be cited on our site? $\endgroup$
    – andselisk
    Commented Apr 8, 2020 at 21:48
  • $\begingroup$ The action of H2O2 on NaOCl has to be one of the better-known reactions. The reaction mechanics is actually more complex than many are aware, but the final products are not in dispute. $\endgroup$
    – AJKOER
    Commented Apr 10, 2020 at 0:20
  • $\begingroup$ Also, do not employ concentrated H2O2, dilute solutions are safer especially in forming normal dioxygen (not singlet oxygen). $\endgroup$
    – AJKOER
    Commented Apr 10, 2020 at 0:27

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