According to Eurekalert, by lowering the pH of household bleach (e.g., by adding vinegar or citric acid), we can increase $\text{[HOCl]}$ and consequently greatly improve the disinfecting capabilities of the bleach itself.

However, doing so could technically liberate chlorine gas, either through hypochlorous decomposition $$ \ce{4H+(aq) + 4OCl- (aq) -> 2Cl2(g) + O2(g) + 2H2O (\ell)} $$ or mere comproportionation $$ \ce{2H+(aq) + OCl- (aq) + Cl- (aq) -> Cl2(g) + H2O (\ell)} $$ (depending on how the bleach was originally made) and so, mixing bleach and acid seems to be contraindicated everywhere else on the internet.

However, the authors of that link also suggest

... first diluting one cup of household bleach in one gallon of water and then adding one cup of white vinegar.

So then does that make it safe? Wouldn't chloroacetic acid formation also be a concern?

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    $\begingroup$ There won't be chloroacetic acid to speak about. As for the rest, in effect you'll acidify bleach to make it stronger and then dilute it to make it weaker, much like a man who takes sleeping pills together with wake-up pills. $\endgroup$ – Ivan Neretin Jun 15 '18 at 11:34

The oxidizing effect of chlorine is quite powerful even at concentrations of 1% or less. Mixing bleach and vinegar gives a much more concentrated solution. Although chlorine is soluble to the extent of 1.46 grams per 100 mL cold H2O (CRC Handbook), its vapor pressure above the water may be significant. A solution diluted by a factor of 7 or 8 would be in contact with a surface long enough to disinfect with a much reduced odor. Safer for people, but still deadly to bacteria.


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