Hypochlorous acid

Can you tell me more about hypochlorous acid as a cleaning/disinfecting agent? Is it safe? Is it effective? Does it keep for a long time?
How does it compare to supermarket cleaners that are cheaper and more easily available?

Thanks so much for your website! I’ve learnt to much.

31960cookie-checkHypochlorous acid

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Dr Chemical
Dr Chemical

Not quite right. At pH of 8.2 the ratio of hypochlorous ion to hypochlorous acid is 5:1 (based upon a simple calculation from its pKa of 7.53). But nonetheless, your point is well-made. A lower pH (below the pKa) will yield a higher concentration of the acid and therefore efficacy of chlorination. I’d aim for 7.0-7.4. Not sure where I heard the 8.2 figure…

Dr Ian Calhaem
Dr Ian Calhaem

The answer by Dr Chemical concerning what is hypochlorous acid is INCORRECT. When bleach (calcium or sodium hypochlorite) has a pH of 8.2 it is ENTIRELY composed of Hypochlorite ions 0 NO Hypochlorous. If the bleach is acidified to a pH value of 6.5 then the Hypochlorite ions change to Hypochlorous Acid. This is a reversible chemical reaction based on the pH of the solution.

wzander
wzander

Bleach is not the same as HOCl. HOCl is more effective than bleach as a disinfectant. A pH between 5.5 and 6.5 is necessary to maximize HOCl.

Dr Chemical

Hypochlorous acid is essentially the active ingredient in bleach. Bleach is NaOCl and hypochlorous acid is HOCl. When you adjust the pH in your pool you are aiming at around pH 8.2. That’s because that’s the pH at which hypochlorous acid is the dominant species. So to make hypochlorous acid all you have to do is get some bleach and adjust it to pH 8.2