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This is a follow up to this question. Here is my short procedure:

  1. start with 200mL distilled water
  2. add 7mL of 8.25% sodium hypochlorite (.11M) to the solution. The resulting solution should be 3.7*10$^{-3}$M NaOCl
  3. add bromocresol green indicator.
  4. add acetic acid dropwise, titrate until the solution hits a green color (pH~5).

I think at this point, the solution should contain HOCl and a small amount of dissolved sodium acetate. $$NaOCl + CH_3COOH \rightarrow HOCl + CH_3COONa$$ I took a pH test with litmus paper and it shows between 5-6. I took a free chlorine test to determine the concentration of HOCl, and it resulted in ~1000ppm, which was what I was aiming for. The chlorine concentration stayed comfortably within its max solubility in water. I used an NaCl meter to determine the concentration in the solution and it returned 0. However, I tested for salts with silver nitrate and it precipitated both white and dark brown/black.

White precipitate indicates presence of chlorine, and dark brown precipitate indicates presence of OH. How did I get AgOH in an acidic solution? Is it simply that the silver rips apart the HOCl to form AgCl and AgOH?

My boss is concerned that I have made dilute hydrochloric acid, not hypochlorous acid. How can I prove that the solution is one product or the other?

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Ryan, sorry your approach to generate the desired compound is not the best one. This post also shows the problems with the concept of an "accepted" answer on StackExchange. The answer is also wrong and misleading. Please consult your academic supervisor to help you do a proper literature search. I am not sure why are you doing all this, you did not explain in your two posts. First of all, there is nothing such as pure 8% NaOCl soln. This bleach is a mixture sodium hydroxide and NaOCl. What you are apparently titrating is the free alkali with acetic acid (which you should not be doing). Simultaneously, the hypochlorite ion is decomposing into other products.

The proper place to do inorganic synthesis research is the library, not Q&A site. A good reference is Kirk Othmer Encyclopedia of Chemical Technology to look up bleach and its properties. Any good library must have it.

In your first question you linked a paper "Hypochlorous Acid as a Potential Wound Care Agent" in the Journal of Burns and Wounds. This journal has a zero impact factor which means this is of dubious quality. There was a reason to avoid organic acid such as acetic acid in that paper. Have you read about disinfection by-products in water? Search this topic this too, because disinfection byproducts can be cancer-causing.

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  • $\begingroup$ Here is the reason why I’m doing this. My boss at work uses copious amounts of cleaning fluid, but since COVID, he hasn’t been able to buy any. He asked me to look into synthesizing HOCl so he could use it in a fogging machine to disinfect the workplace. HOCl meets epa criteria for use against COVID-19. What do you think of this literature? ncbi.nlm.nih.gov/pmc/articles/PMC7315945 Is electrolysis the better approach to making HOCl? $\endgroup$ – Ryan Jul 14 at 8:06
  • $\begingroup$ Vapor-phase hydrogen peroxide is a standard method of microbial decontamination/sterilization for labs, hospitals, etc. Acidified chlorine bleach, which you tried out, or just 5% unacidified bleach, are effective but will leave a solid residue on surfaces. In really challenging situations, such as decontamination of an anthrax-contaminated postal facility, chlorine dioxide gas has been shown to be highly effective, but that is probably overkill in this case. $\endgroup$ – iad22agp Jul 14 at 12:33
  • $\begingroup$ Every university should have a Environment & Health Safety Department. They are best persons to contact for this problem. $\endgroup$ – M. Farooq Jul 14 at 14:49
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The explanation is actually a reaction I once attempted, the reaction of a soluble Silver salt (here Silver nitrate, I experimented with Silver acetate) with HOCl. The reaction apparently per Mellor (see this reference) proceeds, assuming some chlorine per the reactions:

$\ce{ 2 HOCl (aq) -> 2 HCl (aq) + O2 (g)}$

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

further, as follows commencing with the creation of the unstable Silver hypochlorite in an equilibrium reaction:

$\ce{AgNO3 (aq) + HOCl (aq) <=> AgOCl + H+ + NO3-}$

Followed by the disproportionation of the unstable hypochlorite forming a white precipitate of Silver chloride, which moves the above equilibrium to the right:

$\ce{3 AgOCl (aq) -> 2 AgCl (s) + AgClO3 (s)}$

Also, in the presence of HCl:

$\ce{ AgNO3 + HCl -> AgCl (s) + H+ + NO3-}$

The dark precipitate you reported is likely Ag2O formed, I suspect, from the subsequent breakdown of the Silver chlorate (which is a strong oxidizing agent). Less likely, but possible, is Ag2O2, which is also described as a dark brown solid per Wikipedia.

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  • $\begingroup$ Thank you! I guess I kind of split my question into two parts. Does this also prove the presence of HOCl and not HCl? $\endgroup$ – Ryan Jul 13 at 22:58
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    $\begingroup$ Anytime your have Ag+ and a source of Cl-, including from HCl, one quickly gets AgCl(s). So, as long as the Silver ion is in excess, no HCl. $\endgroup$ – AJKOER Jul 13 at 23:24
  • $\begingroup$ so the presence of the dark precipitate means that there was excess silver ions, thus no HCl- thanks! $\endgroup$ – Ryan Jul 13 at 23:51
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    $\begingroup$ @Ryan, Sorry to say all these silver related equations are imaginary, except the HCl one. A misleading answer. $\endgroup$ – M. Farooq Jul 14 at 4:03
  • $\begingroup$ Farooq: Do you known that the action of NaOCl on soluble Pb salts forms a transient Pb(OCl)2? There are pictures on this Lead hypochlorite and its subsequent decomposition producing red PbO2 on warming. I have also performed this reaction. Silver chemistry obviously related as AgClO3 is cited as unstable except in the presence of excess Ag2O, $\endgroup$ – AJKOER Jul 14 at 19:59

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