The thread title pretty much says it all. If i have a container full of hydrochloric acid, will it still be as powerfull in 20 years as it is today?
According to Wikipedia:
Which doesn’t quite address what happens in a glass or Pyrex container.
Acids are strong oxidizers, though, and really wants to form oxides. Again, according to Wiki:
A danger of many acids is that they’ll form a salt that will be a very impact and friction sensitive (but not very brisant, IIRC). Again, this assumes interaction with the environment (which may be simple diffusion through the glass walls?).
If you have a sealed container of aqueous hydrochloric acid (HCl) in an unreactive container with no air space, it will not degrade over time. Similarly, a strong base such as sodium hydroxide will not degrade if sealed in an unreactive container.
The unreactive container can be a sticking point for some acids. For example, hydrofluoric acid (HF) dissolves glass. This is unusual behavior, though. Most acids will not diffuse through or react with glass.
Santo Rugger, I don’t believe that you can extend the instability of a organic weak acid (such as picric acid) to predict the behavior of all acids, particularly strong inorganic acids (such as HCl).
Also, many acids do not form particularly reactive salts. For example, HCl forms chloride salts (e.g. NaCl).
As we seem to have acid/base experts available, I’d like to ask a somewhat related question if I may.
Watching an episode of How it’s Made the other day they mentioned that after aluminum cans were drawn to their final shape they were rinsed with deionized water “which has no Ph”. Now I’m not a chemist, but how can some liquid have no Ph? I can understand having a Ph of 7 which would be neutral, but I would think of no Ph as being lower than one, which would be very acid, right? Is there a simple explanation for a layman? Or did they simply use the wrong term and mean it had a ph of seven?
Thanks.
They used the wrong term. Deionization refers to just the removal of mineral ions from water. Ideally pure water has a pH of exactly 7. If there is any atmospheric headspace, it will absorb CO2 which will bring it just under 7.
It is possible to have negative pH value, because pH is actually the negative log of the concentration of H+ ions. For example if a solution had 10 moles per liter of H+ ions, the log of that is 1, and the negative is of course -1. An example of this would be a 10M solution of HCl (a strong acid that dissociates completely, so a 10M solution of it would dissociate into 10M of H+ and 10M of Cl- in water).
They used the wrong term and meant it had a neutral pH (which is 7.00 at room temperature).
It is impossible for liquid water or aqueous solutions to have “no” pH.
Non-aqueous (i.e. non-water based) solutions may not have a pH, though, since pH is a representation of how much dissociated hydrogen/hydronium ions are in solution.
They just mean a pH near 7. Aluminum is amphoteric so you need to use neutral solutions.
I disagree with this statement. Nitric acid is a strong oxidizer, but that is an exception. Technically, hydrochloric acid will oxidize zinc, but it is not considered an oxidizer. Protons aren’t considered oxidizers because they are defined as acids. Picric acid may be considered a weak oxidizer but I’m not sure. I’ve never seen an organic nitro group used as an oxidizer, but the potential is there.
Also, I would not refer to a pH of less than one as being equivalent to “no pH.” As as stated previously, an aqueous solution cannot have “no pH.”
As you state, it does indicate a very acidic solution.
Also, it incorrect to write pH as “Ph.” The representation has a very specific meaning. FWIW, you can also have “pOH,” “pK[sub]a[/sub],” “pK[sub]b[/sub],” etc., where:
pX = -log
Thanks for all the quick answers. I now understand that my initial thought, wrong word was correct. 
I don’t disagree with the gist of what you are saying, but to expound on this a bit further…
HCl is indeed a non-oxidizing acid, while HNO[sub]3[/sub] is an oxidizing acid.
However, in many reactions with metals, strong acids like HCl do act as oxidizing agents.
The term “non-oxidizing acid” indicates that only the proton reacts, while the anion is inert. More precisely, the term indicates that the anion of the acid is weaker oxidizing agent than H[sup]+[/sup].
Thanks for increasing my understanding, WarmNPrickly and robby.
Is the pH exactly defined as the log of hydrogen concentration, or is it normalized in some way to guarantee that pure water is exactly 7.00000? There’s no reason why a natually-occuring substance would have a precise mathematical value for anything, unless the scale were specifically designed for it to do so.
No normalization; it’s just coincidence that near room temperature pure water has a pH near 7.0. Unsurprisingly, the equilibrium position of H[sub]2[/sub]O <-> H[sup]+[/sup] + OH[sup]-[/sup] is temperature-dependent (moving rightward at higher temperatures like you’d expect), and at higher temperatures the pH of pure water decreases. Here’s a table.
It’s actually a function of the self-ionization constant of water. Ever substance has a self-ionization constant. Water happens to be 1.0×10−14 which solves to produce the pH scale discussed previously. Not to differ from the previous poster, just to focus on why the value is constant… because it’s governed by a constant.
That’s an interesting question that I have never considered. According to wikipedia pKw is actually 13.9965 at room temperature (They use the CRC as a cite). I think that would make a neutral pH slightly lower than 7.0.
In “real life” situations, solutions of NaOH will gradually pick up CO2 from the air and become less basic. Working and stock solutions of NaOH in regulated laboratories have fairly short expiration dates…like one week. After that, they need to be retested to accurately determine their current concentration.
Adding to that, I work in a laboratory that uses fairly concentrated nitric acid. We generally don’t worry too much about those. Everything else (bases and buffer solutions) needs to be kept covered whenever possible, are retested and replaced frequently.
The solid will also pick up CO2. But this only happens if it is exposed to air. In a sealed container, you wont have much of a problem You wouldn’t want to do precision analytical work with it though. If your doing foresics work or something then you’d better follow the protocol on standards in all cases.
Technically the solid picks up water from the air, which picks up CO2. Or am I mistaken? The solid doesn’t have a pH at all.
Hmmm. When I’ve seen it, there hasn’t been any obvious moisture. You can tell because the sodium hydroxide gets crusty. But I know how that stuff picks up water so you could be right. The process certainly generates water.
2NaOH + CO2 —> Na2CO3 + H2O