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Name: Sebastian
Status: student
Grade: 9-12
Location: CT
Country: USA
Date: February 2009


Question:
Hi, I have noticed that my school stores Sulfuric acid in glass bottles. I have also noticed that some labs, and professionals I have seen store it in HDPE bottles. Is there any advantage to one versus the other? Will the plastic contaminate / discolor the acid?



Replies:
The "standard" container for sulfuric acid is glass, even though sulfuric acid can dissolve glass if the surface area is very large. Only is the most precision experiments is this a cause for concern. For short term storage (days - weeks) HDPE is OK but any plastic container is subject to having low levels of polymer fragments and/or additives. In any case if the acid is discolored you can assume it is contaminated, and should not be used.

Vince Calder


Sebastian,

Chemistry labs can be unsafe if the chemicals get mishandled or spilled. Concentrated sulfuric acid can cause really nasty burns on skin (and destroy clothing) as well as eye corneas. As a teacher I am always looking for ways to reduce accidents and risks. Here is where the HDPE bottles come in. These bottles do not shatter. If a person drops a glass container of sulfuric acid (even dilute) there is a high probability the glass will shatter and/or the cap will come off. The result is an acid spill. HDPE bottles have a much lower probability for breakage. That is why chemistry teachers like them.

Warren Young


Sebastian-

I have stored ( concentrated H2SO4 + 3% H2O2 ) for a 3-5 years in the polyethylene bottle in which it was delivered. Eventually it did discolor (tinged brownish), but not until after a few years. The discoloration may have been from eventual degradation of an organic additive to stabilize peroxide, instead of the bottle, but I do not know. On the other hand, the stabilizer before it was consumed might have been preventing the bottle from generating discoloration in the first year. Almost any organic substance which can be de-hydrated and partly oxidized by the acid will build up the brown coloring. Polyethylene is not particularly prone to that, but it is not inconceivable either.

I have personally had an old poly bottle (pint) for hydrogen peroxide which, after I discarded the expired chemical, allowed its bottom to be neatly cracked away from the walls. So there was a danger of sudden spillage. Sulfuric might have some of this effect on poly, on rare old occasions. On the other hand, in the short run a poly bottle is much more break-resistant when dropped. If my gallon bottle is glass, I am more comfortable if it has that elastomer safety- coating on the outside, even though that coating gets a bit sticky. But I do not really get that coating often.

If I seem to be slurring the distinction between Sulfuric Acid and Hydrogen Peroxide, I do know the difference, but there is a relationship. The dehydrating potential of the H2SO4 is fairly stable, and always helps oxidation reactions. But I tend to think that for a given old bottle of the acid, the oxidation potential of the solution is variable and unknown. It could be H2SO4 + 0.1% H2SO3, somewhat reduced and not highly oxidizing, (< 0.2 volt ) or it could be H2SO4 + 0.1% H2SO5 (Caro's acid), and have a real knife-edge for slow but powerful oxidation (> 1.0volt). I think the 0.1% H2SO5, if about 1% water is added, becomes 0.1% H2O2. It is an equilibrium relationship, and the two (Caro's and peroxide) are roughly equivalent.

A very small concentration of silica, Na+, and Ca+ might dissolve into the acid from a glass bottle. In some very sensitive applications this might be more undesirable than a similarly small concentration of suspended carbon-rich substances.

I would tend to accept either for a given year of use. Older acid would stay clearer in glass. An old poly bottle might be weak or leaky; be cautious. I suppose the professionals you noticed make a presumption that their bottles will be used up at a steady pace. In return they get lower ionic contamination and lower risk of breaking-spillage in a workers hands. That's about all I know about it.

Jim Swenson



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