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spirocycle
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[*] posted on 29-9-2010 at 18:13
sulfuric acid turned black


I've been keeping about a liter of conc. sulfuric acid in the original HDPE bottle in a drawer for some time now, and I just checked and the bottle is all black
is it still usable?
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Magic Muzzlet
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[*] posted on 29-9-2010 at 19:22


Probably.
What condition is the actual acid in? And how long has it been in the drawer? Might be a good idea to transfer it to a glass bottle too.
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[*] posted on 29-9-2010 at 23:29


Likely it's an oxidation product from the plastic or more likely from the lid gasket.
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spirocycle
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[*] posted on 30-9-2010 at 10:33


its been there for almost a year now, haha
I dont have any glass bottles large enough for it
o well, ill just buy another bottle
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[*] posted on 1-10-2010 at 22:38


That's organic contamination.

It's either come form something happening to the bottle (unlikely if it's HDPE) or something organic has gotten in there by some other method. If it had a dye in it when you bought it, the DIY stuff I buy is pink for example, it may have broken down over time.

It won't affect the performance of the acid in any major way. There are ways to remove the black, but they're fairly dangerous if you can't identify the black and work out the future uses in the first place.

[Edited on 2-10-2010 by peach]




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HydroCarbon
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[*] posted on 5-10-2010 at 15:33


Probably still usable if purity isn't a big concern for you. Highly technical grade :P.

Best to transfer it to another bottle if you want to use it further. Glass or HDPE, check the caps for incompatible materials.


Can sulfuric be stored in stainless steel? I think I may have heard that somewhere.
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[*] posted on 5-10-2010 at 15:57


Nah, stainless isn't a great plan. At the very least it's going to contaminate it's self with metal traces.

304 is very slightly better than 316 for handling it. A problem with stainless is all the different metals in there forming a galvanic cell that is only helped along by the acid. That may be why 316 goes a bit quicker in it, because it has molybdenum in it whereas 304 is mainly chrome and nickel.

Glass is obviously great in terms of reactivity, but the people who sell me chemicals have managed to smash reagent bottles before they ever reached my door, providing an indicator for why so many guys are using HDPE. I've also heard those stories of the bottom dropping out of glass reagent bottles full of it. Personally, I would bet one English pound on that being a fault with the glass as opposed to the sulphuric inside it.

HDPE is about as good as it gets for chemical resistance from the plastics. From there, you have to go to the fluoropolymers, and then the bill goes vertical in the wrong direction.

There seems to be a quite a few posts about storing sulphuric. Just use the damn HDPE bottles it came in and don't balance it over your head on the shelves with the cap loose.

mol... moly-lib-donum? mo-lib-denum? moly... fuck it, moly. :P




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[*] posted on 5-10-2010 at 18:15


yeah, PE is way more chemical resistant than most people give it credit for.

[Edited on 6-10-2010 by HydroCarbon]
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[*] posted on 5-10-2010 at 18:23


thanks for the advice guys,
helped out alot
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[*] posted on 25-11-2013 at 16:13


can the black stuff (carbon?) be removed by oxidizing it by heating the acid?
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[*] posted on 25-11-2013 at 16:48


Just a thought: heating conc. H<sub>2</sub>SO<sub>4</sub> is a bit hazardous. Have you considered trying to filter it through a PTFE membrane or other acid-resistant material?



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[*] posted on 25-11-2013 at 18:01


It’s not worth it, considering the price of a PTFE membrane or a glass fiber filter paper I would rather order the acid online. I’ve watched a video on YouTube that the carbon may be removed by adding some H2O2 and then heating the acid. I think it’s worth to give it a try.

Also, will sulfuric acid eat through normal filter paper at any concentration? I haven't made a titration of my acid but I'm pretty sure it's not concentrated because of viscosity.
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[*] posted on 25-11-2013 at 18:53


Not at <em>any</em> concentration; but at higher concentrations, yes. Test a circle of your filter paper with a couple drops of your acid.



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[*] posted on 26-11-2013 at 09:53


Quote:
can the black stuff (carbon?) be removed by oxidizing it by heating the acid?

Aliphatics are readily oxidised by boiling H2SO4─ evolving CO2 which bubbles off.
Aromatics, however, are resistant, being oxidised only slowly!




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mad.gif posted on 9-12-2013 at 13:17
Getting Carbon Out of H2SO4


Im a DIY chemist like most members and I would like to ask a stupid question. Can you get the black crap out of cheep acid?
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[*] posted on 9-12-2013 at 13:28


Yes use a filter and if that doesnt work (it depends on particle size) than there are harder ways, but try that first.



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[*] posted on 9-12-2013 at 13:30


As an FYI, concentrated H2SO4 attacks common filter paper. Whatever is used, it has to be resistant to acids.

[Edited on 9-12-2013 by WGTR]
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[*] posted on 9-12-2013 at 13:34


It dehydrates it spectacularly, but it depends on concentration. He could only use paper if it is dillute.

[Edited on 9-12-2013 by bismuthate]




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9-12-2013 at 13:42
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[*] posted on 9-12-2013 at 14:20


bismuthate: your last comment was incorrect in my experience. if room temp or cold, I have been able to filter CuSO4 from strong acid just fine with coffee filters. but with a good heating it will BLOW RIGHT THROUGH a paper filter leaving only a charred edge around the hole. that was found out first hand after boiling down the acid to concentrate it. I had been messing around with electrolysis of copper in H2SO4 because at the time I couldn't afford to drop 20$ on a pound of root killer for a plating project. I tried to save some time by boiling it down to reduce the amount of liquid to filter and it kinda scared me. all the copper sulfate that was in the filter from the first batch fell right out the bottom of the funnel leaving the hole and turning the acid black. made me think about what would have happened to my skin should some glass decide to shatter on me.

after decanting most the CuSO4 off at low temp, I clarified the acid with 3% hydrogen peroxide. it diluted the dark acid and bubbled lightly. I left it on low heat to speed the process. the blue acid( some CuSO4 dissolved still ) was then chilled and filtered again. it was still light blue but clear, not dark at all after concentrating it again.

H2O2 also clarified the solution from leaching banana peel ashes for K2CO3. the left over organic mater, only partially burnt banana peel made the leached sol. a dark honey color. after the treatment it was only ever so slightly yellowish after boiling down. so it seems to be quite good at removing carbon residue as CO2

there is also this:
http://www.google.com/patents/US2866684
talking about clarifying H2SO4, it mentioned cloudy acid can be a result of suspended particles which were suggested to be iron contamination. may help further purifying acid from the hardware store.
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[*] posted on 9-12-2013 at 15:13


Oh I didn't know that.
Jmap science, how concentrated is your acid (out of curiosity)?
Also can you distill H2SO4? (I don't plan to) I've never heard of one doing so.

[Edited on 9-12-2013 by bismuthate]




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[*] posted on 11-12-2013 at 06:20


Its 98% con.
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[*] posted on 12-12-2013 at 04:26


bottom dropping out of a glass container with H2SO4

not sure if that tops dropping 500g MnO2
there should kinda be a thread on chemists nightmares?!?

once was so damn clever to stir my newly concentrated H2SO4 (+70%) with a wooden stick as i used to do this when it was below that conc. i quickly realised that it wasnt a good idea to do that anymore.. those particles looks too small to seperate out by any means.. i dont suspect (nano?)particles of carbon in H2SO4 will ruin its performance or usefullness however?
not a problem for at least most chemical reactions.. (:




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[*] posted on 12-12-2013 at 04:37


The problem I see is that if he made MgSO4 for example when it's evaporated there would be a lot of carbon in the crystals.




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[*] posted on 20-6-2015 at 06:57


I know this is really old, but I had this problem these days and it´s really easy to solve once you know what to do ;)

1. I diluted the H2SO4 with water until it would stop eating my filter papers (ordinary coffee filters)
2. I filtered the diluted H2SO4 with 5 filters (putting one into the other and so on)
3. I put the filtered solution on a heatplate and let evaporate most of the water by heating around ~80°C
Now this is funny, in this stage it got totally clear (typical light yellowish solution), BUT if let it too much time on the heatplate it turns black again, this time without visible particles in it. So I tried out the reaction with H2O2 and it worked like a charm.
So, if your solutions turn black again while concentrating, make step 4 as well.
4. Add about 20% of its volume of H2O2, and despite what I read here, 3% H2O2 works just fine.
And be carefully, as all mainly water based solutions, putting 3% H2O2 into concentrated sulfuric acid will heat up the solution and could lead to spills beacause of spontaneous boiling.
5. Heat the solution and in a few minutes it should bouble a bit (like water with gas).
6. Let evaporate all the water containing in the solution.

-> You should have about 98% H2SO4 by now.


Happy H2SO4 clearing :)
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