Outlander
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Problem concentrating H2SO4
I'm not sure where this belongs, so i posted it here. I've been googling but have yet to come up with an answer.
When I need concentrated H2SO4 for experiments I typically boil down new battery acid until my thermometer reads around 320C, It usually takes around
2 - 3 hours and it's clear with a slight yellow tinge to it. However I run out recently and bought another (different brand) bottle of battery acid -
S.G 1.26 - and have been having problems (one of which is that I broke my last 360C thermometer and cant get more for a couple of weeks):
I put 700ml 36% H2SO4 into a 1lt beaker and heated it in a sandbath on an electric hot plate, a couple of hours later it had hardly reduced at all and
there was no sign of it boiling, so I removed the sand bath and placed the beaker directly on the hot plate, an hour later, still no boil. So I
thought the hot plate must have been on it's last legs (although it's only relatively new) so I put the beaker back in the sand bath and put in on a
portable gas cooker for 50 minutes on 'high', Still i could not get it to boil. Annoyed, I covered it and let it cool then bottled it, once it had
cooled to room temp, I measured exactly 10ml and weighed it, Density was 1.64g/ml or around 75%.
The next day i poured it back into the 1Lt beaker and put it back on the electric hotplate in a sand bath, I turned the hotplate to 'Max' and left it
to heat up - a lot of white vapor was coming off - I then set up a fan to blow over it to speed up evaporation since there was very little wind, I
left it for 3.5 hours after which it still hadn't boiled and had only reduced around 50ml - Also the colour had become a LOT darker than i am used to,
I removed it from the heat and set it aside to cool, once cooled to room temperature I again measured exactly 10ml of it and it weighed only
1.681g/ml. So for 3.5 hours of heating, a hell of a lot of white gas coming off and loosing at least 50ml it had only increased from around 75% to
maybe 78%?
Can someone tell me what i'm doing wrong? I've done this 4 or 5 times before with the same setup, but different acid, and never had a problem.
[Edited on 23-4-2010 by Outlander]
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hissingnoise
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It's many years since I boiled down battery acid but I remember an amber colour appearing - darkening as the volume reduced.
When the very dense white fumes appeared the acid evolved small gas bubbles (CO2), went water-white and deposited a white precipitate.
The precipitate was SiO2.
SiC had been used in the acid to prevent crystallisation occurring between the battery plates.
Bringing the acid to 98% had oxidised SiC to CO2 and SiO2.
Try reboiling your acid until opaque white fumes appear; you can then assume it's 98% without checking its density.
In any case, a hydrometer is a bit more accurate than weighing samples!
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DJF90
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If you've boiled it past the point of white vapour being evolved then you've lost some of your acid! You're supposed to stop when the white fumes
become apparent.
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Outlander
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Thanks for the replies.
The last few times I boiled it down i began noticing white fumes at about 150C, they steadily increased until the B.P reached 300+ at which point they
were quite thick, so if i stopped when the white fumes began i'd have around 65% or maybe less.
From 700ml of 35-36% it should reduce to around 245ml 98%, yes? However it seems nothing I do can get it below roughly 400ml (and so far I've found it
impossible to boil, even at it's starting strength which should boil at ~125C) all it is doing is going darker and throwing off white clouds that are
visible for about 50 meters as they drift away, I also doubt it's already at 98% since it's hard to believe 50%+ H2SO4 would be bottled as 35% battery
electrolyte.
I'll have a look to see if i can get a hydrometer when i order more thermometers, but since that will be a couple of weeks away, I'll attempt boiling
it again over a gas flame. Also I checked my hotplate and it appears to be working fine, It takes 10 minutes from first being turned on to heat 750ml
of cold water to a rapid boil which is the same as when it was new.
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Skyjumper
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Why not use drain cleaner H2SO4, Its already concentrated.
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Outlander
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It's not sold here, it was hard enough getting a bottle of battery electrolyte.
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hissingnoise
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| Quote: | | I also doubt it's already at 98% since it's hard to believe 50%+ H2SO4 would be bottled as 35% battery electrolyte. |
It's just possible that it is 50% and was intended to be diluted before use.
But not having access to draincleaner is a problem - can you get someone to order it for you; a pharmacist, maybe?
You could say you have a badly blocked sewage-pipe or something. . .
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rrkss
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Question, do you use any sort of boiling chips? I had this problem a while back and adding boiling chips solved the problem.
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Outlander
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No boiling chips. To date I've never had a problem with H2SO4 bumping so i haven't worried about them, I'll add them to the shopping list anyway since
they'd be nice to have on hand.
Hissing noise, thanks for the suggestion, I lurk here quite a bit and always find your posts interesting. Unfortunately I try and keep my hobby as
low-key as possible, it seems these days if you have so much as a beaker you must be a meth cook or Taliban timmy, I asked my pharmacist for KMnO4
(10g) last year and had to show I.D and have all of my details recorded. Also the acid is just labeled "Battery Grade Sulphuric Acid - Specific
Gravity 1.260".
Edit: I just checked the MSDS (I know, i should have done it first) and it says:
Sulphuric 20% - 60%
Water 40% - 80%
That seems like VERY lax quality control, to the point that there is no use even printing a concentration/SG on the bottle, I guess i'll just have to
leave it on the shelf until i can get more 360C thermometers and a hydrometer.
[Edited on 25-4-2010 by Outlander]
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rrkss
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The boiling chips just give me a faster and steady boil. I've not really had a bumping problem either but they do help a ton. I recommend the
pourous graphite ones for sulfuric acid.
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hissingnoise
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I've never used boiling chips for sulphuric acid because I use a shallow pyrex dish without lid.
~rrkss, as stated in a previous thread, H2SO4 reacts with graphite, to some extent.
~Outlander, if your battery acid doesn't contain interfering additives the thermometer and hydrometer shouldn't really be neccessary since the thick
vapour will tell you when 98% is reached.
If you do get a hydrometer, a tall cylinder is needed to accommodate it.
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The WiZard is In
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Just put it into a graduated cylinder and weigh it.
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Outlander
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I have a 25ml and 100ml glass measuring cylinders as well as a couple of 100ml HDPE ones.
I used the 25ml cylinder with 0.5ml graduations and a scale of 0.01g accuracy to measure the density before and come up with 1.681g/ml.
I'm interested as to what these "interfering additives" are and how they can be beaten, could this explain why I was unable to make it boil at any
stage?
[Edited on 26-4-2010 by Outlander]
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hissingnoise
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ISTR, various additives have been used in BA to prolong battery-life.
They were metal ions, I think, but whether they'd prolong battery-life or interfere with boiling the acid is probably a moot point.
Using a pyrex dish, I've never seen H2SO4 boil visibly - I rely on the vapour to tell me when the acid is virtually anhydrous.
The large surface-area seems to help in removing water. . .
Doing it in humid conditions means the acid needs to be bottled and capped asap.
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DJF90
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| Quote: | | I used the 25ml cylinder with 0.5ml graduations and a scale of 0.01g accuracy to measure the density before and come up with 1.681g/ml
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You can't quote to that many significant figures because your accuracy isn't to that degree. The best you could do would be 1.68g, but even then it's
pushing it, especially with such a large error on the volume part. Use a 10ml measuring cylinder graduated to 0.2ml or even better measure from a
burette into a tared container.
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Outlander
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I measured 10ml (give or take, say 0.25ml) which gave me 16.81g, divided by 10 gives 1.681g/ml and the extra decimal place, I did this to minimize
error and the extra number is really insignificant.
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rrkss
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Just did a small test run boiling down battery acid in my 1000 mL florence flask on my hotplate using graphite boiling chips (I know they supposedly
react with the acid but never caused me any problems). After about an hour, the acid gave off thick white fumes that were so dense that I could no
longer see through the boiling flask. The acid itself was a clear pale yellow color.
I let the acid cool and when it no longer gave off white fumes, I attached a drying tube to the flask. Once at room temperature, I titrated 1 mL of
acid with 1.00 N NaOH solution and it took 37 mL for the phenophalein solution to turn pink giving me a molarity of above 18 or 98% sulfuric acid.
[Edited on 27-4-2010 by rrkss]
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peach
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That does sound odd.
Is the different brand of acid labeled as specifically for use in batteries? If not, it could easily have something else in it that's interfering.
I believe brick cleaner is often HCl, but the 5l bottle of it I found lying around from the building work we've had done smells like one of the
builders has bottled a beer fart in there, suggesting it's sulfuric. That would also seem in keeping with the powers that be trying to keep nitrating
/ halogenating acids out of the hands of the noobine.
The brick cleaner also had a few additives included, designed to improve the process. I think they're some kind of surfactants, haven't really
bothered looking since I can get about as much battery acid as I'll ever need.
This could be akin to using undistilled nail polish remover as a solvent and wondering why it's not behaving it's self, with all those essential oils
and nail conditioners in the pricier versions.
"Good morning sir, which of our fantastic new range of nail conditioners and paint strippers can I interest in you today?" "The dirtiest, cheapest
stuff you stock please!"
You're getting fairly technical on your concentration. I just stick the stuff in a pyrex dish and put it straight on the hob. When you start coughing
and the neighbors come out to see if your place is on fire, it's done. 
Worth noting that home anodizing and plating kit suppliers often have, or know where you can easily buy, acids.
If you're having trouble finding the sulfuric online, get out the house and down to a few local garages. Tell them your refilling a golf buggy and
that you need 36 gallons. And that you need to do some plating, and maybe clean some brickwork, and unblock a drain. Make some comments about engine
maintenance or 'dyno pulls', turbo chargers and nitrous; like "I saw a toyota supra pull 1300 on a dyno, awesome ride! My car is lame, and so is the
size of my penis. You have much mightier peni!". Don't forget to mention how sweet their setup is; preferably making note of how expensive that tire
balancing machine must have been. Ask how it works. You'll get it then, both the acid and a long explanation of dynamic balancing. 
[Edited on 1-5-2010 by peach]
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