Strength
Available chlorine: typical bleach strength vs typical HOCl strength
CDC-cited bleach protocols run from about 100 to 5,000 ppm. The HOCl-type solutions in the studies cited here mostly sit in the tens to a few hundred ppm.
Free chlorine in water exists as two main species: hypochlorite ion (OCl⁻), and the undissociated acid, HOCl. They convert into each other as pH moves. Household bleach and HOCl-type solutions both start from that same equilibrium. The comparison on this page is about where each one usually sits on the pH scale, and which species ends up in the majority.
For a general introduction to the molecule, see What is hypochlorous acid? on disinfectant.org. For the pH curve itself, see How pH affects HOCl.
Where each one usually sits
| HOCl | Bleach | |
|---|---|---|
| Typical pH | Slightly acidic electrolyzed solutions about 5–6.5; neutral ones about 6–7; strongly acidic types about 2–3. | Alkaline (above pH 8 for CDC's tap-water dilutions; 9.3 to above 11 in the cited studies). |
| Majority species | Undissociated HOCl near pH 5–6. | OCl⁻ at alkaline pH. |
| What changes the split | pH, not the way the solution was made. | The same rule: lower the pH and the HOCl share rises. |
Why the source matters less than the pH
A solution can reach the HOCl band in several ways: from a generator, as a buffered commercial product, or by acidifying bleach in a lab. At the same pH and the same free available chlorine, those three hold the same HOCl / OCl⁻ split. That is why papers that bring bleach down to pH 5–8 report the same pH-linked shift as papers on electrolyzed water (see Mixing for why that is a lab finding and not something to try).
CDC describes chlorine’s activity as “attributed largely to undissociated hypochlorous acid,” and notes that it falls as pH rises, in step with the conversion of HOCl to OCl⁻ (CDC 2008, p. 41). In one study that tracked the two species directly by UV measurement, HOCl concentration peaked near pH 4 (Len 2000). The same authors point out that “standard titrimetric methods… cannot differentiate the levels of HOCl,” so an ordinary chlorine reading tells you how much free chlorine is present, not how it is split. The Available chlorine page picks up that point.
The alkaline side has its own role. A review notes the general view that the concentration of OCl⁻ “is a key factor determining the cleaning efficiency,” and that the best pH for one job is not the best pH for the other (Fukuzaki 2006).
The short version
Same family, different pH. Bleach is the alkaline end and is mostly hypochlorite ion; HOCl-type solutions sit near neutral or slightly acidic and are mostly hypochlorous acid. If the naming question is all you need, see Is hypochlorous acid the same as bleach?.
Sources: CDC 2008, p. 41; Len 2000 (PMID 11079696); Fukuzaki 2006 (PMID 17190269). Full entries on Sources.