Glass versus HDPE for H2SO4
Date: February 2009
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?
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.
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
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
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
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
A very small concentration of silica, Na+, and Ca+ might dissolve into the acid from a
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
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
That's about all I know about it.
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Update: June 2012