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Can $32\%$ ($20$-degree Baume) hydrochloric acid (typically found as 'muriatic acid' in hardware stores) be stored in a milk jug?

muriatic acid

milk jug

I have read that acids can be safely stored in polyethylene bottles. The milk jug I have has the HDPE resin ID code on it. However looking at Wikipedia, it is clear that HDPE is used to make a wide range of products with different "strengths". Given the "squishiness" of milk jugs, I would assume it is on the lower end of the "strength" scale. Does this make it any less suitable for holding diluted hydrochloric acid?

Context: I plan on etching some circuit boards as per this tutorial. And I am looking for places to store the resulting copper (II) chloride solution.

$$ \ce{Cu + 2HCl + H2O2 -> CuCl_2 + 2H2O} $$

I am assuming that if the container can hold hydrochloric acid, it can hold the resulting copper(II) chloride solution.

A.K.
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Jet Blue
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    I guess there'd be no problem, but you can easily get more solid HDPE cannisters. Just google it. Anyway, please label you bottle properly. Spray it in yellow with a pink skull on it, so everybody get's it that this is not to be openend, spilled, drunk, etc. – Karl Sep 07 '18 at 19:03
  • Is everyone etching circuits for some weird reason? https://chemistry.stackexchange.com/questions/662/handling-and-storing-sodium-hydroxide-hydrochloric-acid-hydrogen-peroxide-and https://chemistry.stackexchange.com/questions/35185/how-do-i-store-hcl-safely https://chemistry.stackexchange.com/questions/83845/how-to-properly-store-acids-at-home – Mithoron Sep 07 '18 at 19:05
  • https://chemistry.stackexchange.com/questions/60946/is-it-safe-to-store-muriatic-acid-hydrogen-peroxide-and-acetone – Mithoron Sep 07 '18 at 19:06
  • Can't you store it in the vessel it's stored in when you purchase it? – Todd Minehardt Sep 07 '18 at 19:15
  • @ToddMinehardt I would except, I won't use all of it... and I don't want to mix the "pure" with the "used" – Jet Blue Sep 07 '18 at 19:18
  • @Mithoron ah that's funny. I had come across two of those articles but was curious about milk jugs. The rust shown in one of those questions is alarming! Is the milk jug more "permeable" than a "stronger" container? Is the copper (II) chloride that potent, or is HCl a special case? – Jet Blue Sep 07 '18 at 19:21
  • @Karl, the prices I am seeing on amazon are astronomical... where do people typically buy these canisters? – Jet Blue Sep 07 '18 at 19:24
  • Hm. I find a dozen online sources for 5€ within a second. You local hardware store? Agricultural supplies? There you should get them for 2€. I can get one filled with 5 liters of new wine for ~10 at every other corner at this time of the year. – Karl Sep 07 '18 at 19:36

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There is more than just material composition to container selection. Yes HDPE is compatible with hydrochloric acid, but you have to consider rigidity and failure probability. Think: would you want to store Concentrated Hydrochloric acid in a 2 mil bag? Probably not because the probability of puncture and resulting loss/cost from the spill would be sufficiently high. Though not as extreme your milk jug is along those lines as it is softer and less rigid as the original container.

There is also the issue of legal considerations. In the US I'm sure that milk jug would not meet the DOT requirements for transport, and OSHA prohibits using containers typically used for food as being used for chemical or waste storage.

That said for home use only, you will probably be okay to store it, certainly not recommended, but this is the real world. I would at least recommend that if you do use a milk jug, you at least use a basin that can hold all of the contents for secondary containment in case of a leak which milk jugs occasionally do AND certainly label the contents.

A.K.
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    I like the reminder about secondary containment. You could also put the milk jug in a plastic bag and tie the bag top to help contain vapors of HCl. Milk bottle tops are not really snug, especially after use, and HCl tends to corrode things before dissipating. – James Gaidis Sep 08 '18 at 13:01
  • Another important consideration is the effects of wall thickness on HCL escaping from the container, as it's happening even with thick-walled HDPE containers. It's certainly ok for short-term storage, but without knowing the actual impact I would definitely consider getting a better container for long-term storage, and also ensure that it's not stored on or near materials that would be quickly corroded by HCL. – Thomas Guyot-Sionnest Sep 20 '23 at 22:38
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I prepared the very same etching solution you mentioned to make a custom shield for an Arduino project (it worked great by the way) and still have the etching solution sitting in my garage. It's in a small HDPE tote and has been for over 9 months without any problems. However, the tote has thicker sidewalls than a milk jug. I wouldn't worry about the chemical compatibility and would worry mostly about structural integrity of the container. It might be wise to buy a thicker walled HDPE or Polypropylene (PP) container at the dollar store.

Veluminum
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  • Thanks for the reply! Does your tote have a cover (liquid and air tight)? Doing a google image search for "HDPE tote" and can't quite picture what you have. Also did you experience any problems with the muriatic acid and rust? It seems to be a common problem with storing the acid... and people resort to storing it outdoors =/? Glad to hear the etching process works! – Jet Blue Sep 07 '18 at 22:52
  • I looked for a photo of the kind of box/tote I bought and couldn't find one that matches well. If I find a good image of the box/tote I used, I'll post it. It does have a lid, but I wouldn't trust it to be waterproof. Now that I think more about it, the Muriatic acid I used is this one. https://www.osh.com/Osh-Categories/Outdoor/Outdoor-Living/Pool/Hot-Tub-%26-Pool-Chemicals/Kem-Tek-2X1-Gal-Pool-Muriatic-Acid/p/2821262 It comes in two one-gallon milk jug like containers. The walls are thicker than you would find on a normal milk jug. – Veluminum Sep 07 '18 at 23:01
  • It looks like a tiny version of this. http://zamza.info/plastic-boxes-with-lids/plastic-boxes-with-lids-plastic-boxes-with-hinged-lids-uk-small-plastic-container-with-lid-and-handle/ – Veluminum Sep 07 '18 at 23:06
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According to this chart from a manufacturer of plastics, HDPE is resistant to concentrated $\ce{HCl}$ acid as well as to copper salts (other manufacturers report the same - Google if needed). As mentioned in the comment thread, do be sure to label and store the containers properly.

Todd Minehardt
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