I have water contaminated with dissolved chlorine:

$\ce{H2O + Cl2 <=>HCl + HOCl}$

During electrolysis, this is an issue. These are my products:

$\ce{NaCl + H2O ->T[electrolysis] NaOH + Cl2 + O2 + H2 }$

However, $\ce{NaOH}$ will be neutralised by $\ce{HCl}$:

$\ce{NaOH + HCl-> NaCl + H2O}$

I guess this can be considered hydrochloric acid. I want to remove the chlorine ions from water and prevent future dissolving.

Does increasing temperature help to remove the chlorine? Does boiling make the chlorine leave the mixture?

$\ce{H2O + HCl + HOCl ->T[???] H2O + Cl2(gas)}$

PS.: I understand that there are means of separating the electrolysis columns. But this question is really about removing $\ce{Cl2}$ or $\ce{HCl}$ from aqueous solution.

  • $\begingroup$ Can you let the mixture sit and ventilate for a while? If the chlorine leaves as a gas eventually it will all be gone. HCl should be less soluble in hot water so heating will drive it off faster. $\endgroup$ Commented Sep 7, 2014 at 2:52
  • $\begingroup$ I actually used to put an old PC ventilator on half of the glass, so air would forcefully strike the solution. But even after it smelled, as well as after boiling. Still thanks for info. I'll repeat the process. $\endgroup$ Commented Sep 7, 2014 at 9:27

1 Answer 1


1) Do NOT heat the solution, if you want chlorine out. Electrolysis of hot $\ce{NaCl}$ solution produces $\ce{NaClO3}$, then $\ce{NaClO4}$, not chlorine. You apparantly don't want this.

2) traditionally, in such setups some barrier between cathode and anode spaces is used. The easiest one would be unglazed ceramic pot (with no holes and no direct contact of anode and cathode solutions), though I'm not sure if it will work with chlorine ions. It is recommended to perform electrolisys of $\ce{MgSO4}$ solution first. In this case chlorine ions would migrate from cathode space. With barrier introduced you may expect chlorine to evolve from anode space and sodium hydroxide to accumulate in cathode space.

3) do NOT blow air atop sodium hydroxide solution. It reacts with $\ce{CO2}$ from air.

  • $\begingroup$ Thanks for warning me - apparently, I was totally unaware that I'm dealing with poison. Since the sodium chlorate decomposes at 300°C, it will be best to toss my current product. $\endgroup$ Commented Sep 9, 2014 at 11:52
  • 1
    $\begingroup$ @TomášZato I wouldn't call chlorates a potent poison. They are potentially dangerous in mixes with reducers, but not extremely toxic. $\endgroup$
    – permeakra
    Commented Sep 9, 2014 at 13:36

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