I have been preparing bleach disinfectant lately in a spray bottle and has been spraying on my couch, door mat, door knots, etc... I don't rinse it... So I assume there is bleach residue left after evaporation? Is it safe to leave the residue?
I felt some very mild burn like feeling on my arms when putting my arms on my couch lately; I don't know if this is some kind of placebo effect or if it is real.
Bleach, especially employed in laundry applications, may have, in addition to the active ingredient sodium hypochlorite (NaOCl), an equal concentration of NaCl (as it is prepared from the action of Cl2 on NaOH) and at times, an alkaline, like lye (NaOH) or Washing Soda (sodium carbonate, Na2CO3). The latter can cause skin rashes and irritation (and will be present on drying).
The rationale for the latter is to keep the pH elevated in aqueous sodium hypochlorite as upon exposure to CO2, there is the possible introduction of hypochlorous acid. While HOCl is more powerful (and reportedly nearly a hundred times more potent disinfectant than the associated hypochlorite) is far less stable (a short shelf-life). Further, the decomposition product is O2 and also HCl (and not NaCl).
The created hydrochloric acid can further react with the sodium hypochlorite or hypochlorous acid as follows:
$\ce{HCl + NaOCl -> NaCl + HOCl}$
$\ce{HCl + HOCl <=> Cl2 + H2O}$
leading to a chain decomposition of the bleach, hence the advantage of adding NaOH or Na2CO3. To quote the cited source:
The pH has a significant effect on the stability of sodium hypochlorite solutions. Below pH 11 the decomposition of sodium hypochlorite is significant due to the shift in the equilibrium in favor of the more reactive hypochlorous acid. A pH between 12 and 13 gives the most stable solution. This equates to 0.4 to 4.0 grams per liter (gpl) excess NaOH. Greater concentrations will not improve the stability. Excessively high improve the stability. Excessively high alkalinity will damage textiles and retard the bleaching and disinfecting actions of the hypochlorite.
I would suggest that you can even dilute your current NaOCl dosing and add some lemon juice, just prior to use, to create (per the source reference noted above) a much more powerful mix (and a more potent bleaching agent, so be careful where you select to employ it) albeit, with a much shorter shelf-life.
To rapidly remove bleach smell (likely Cl2O from the dehydration of HOCl), one can apply a spray of dilute H2O2, which rapidly converts NaOCl to NaCl and oxygen. Caution: this further promotes bleaching action via intermediate radical formation (see 'Hydroxyl radical from the reaction between hypochlorite and hydrogen peroxide'), so again be careful where you apply it.
Bleach is usually a mixed solution of sodium hypochlorite NaClO and a lot of sodium chloride NaCl. NaClO is decomposed when dry. So your couch is probably soaked in salt (NaCl). It may produce an uncomfortable feeling.
