RogueRose
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Comparison of H2SO4 & oxalic acid for making acids (price & result comparison)
So I am trying to figure out which acid is more economical for making acids from various salts and am looking at oxalic acid and sulfuric acid. The
prices are about $25 for 10lbs of oxalic acid C2H2O4 and about $28-30 for 1 gallon of sulfuric acid, H2SO4 (~90-94% - 1.84g/ml @ 100% so ~6.4KG acid
or 14.1lbs of 100% acid when water content is removed).
Now oxalic acid is available in anhydrous and dihydrate, the dihydrate being 40% heavier (90g vs 126g anhydrous vs dihydrate) or a loss of 29% in
weight when dehydrated to anhydrous.
Now both acids have 2 hydrogen atoms so in this case, they seem equal, but when it comes to price per hydrogen atoms, the oxalic is much more
expensive, especially if the oxalic being sold is the dihydrate (often not stated which it is, so I'm guessing most are dihydrate). Even if buying
50lb bags, the price is still $25-26 which seems odd.
Now I've seen that oxalic acid can be used to make things like nitric acid from various nitrate salts and one that I think is interesting is Ca(NO3)2
because calcium oxalate has VERY low solubility in water (less than 1mg per liter!). Using H2SO4 to make HNO3 from Cal nitrate leaves a lot of very
fluffy CaSO4 which is a mess to deal with and a lot of HNO3 adheres to the CaSO4, leaving a very dilute HNO3 which has a fair amount of CaSO4
dissolved in the solution (enough to be a problem in many cases). Looking at sodium oxalate, it has a fairly high (30g – 63g per liter) solubility
in water so these seem unsuitable for this use and potassium oxalate is not listed anywhere as a compound (potassium hydrogenoxalate is, but little
info available).
So while more expensive that sulfuric acid, it may be the ideal choice for making HNO3 from calcium nitrate, I will have to do some testing to see if
this works out. IDK if there are other reactions where oxalic acid would be the preferred acid for use and would be interested in hearing from others
who have experience with it.
I'll be posting the results of the calcium nitrate/oxalic acid reaction within a week I hope. If anyone has any suggestions before I try this, please
let me know! Thank you.
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CobaltChloride
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Sulfuric acid can also be successfully used to make fairly pure nitric acid without distillation. You need to buy barium nitrate from a fireworks
supplier (pretty easy to find one if you're in the USA, but harder if you're in Europe). If you react this with sulfuric acid, you'd get nitric acid
and barium sulfate. Barium sulfate is incredibly insoluble in both nitric acid and water, so you'd get fairly pure acid. This precipitate isn't as
fluffy as CaSO4*2H2O because it has much higher density. It will eventually settle out, so there's no problem if you have no acid-resistant filter as
you can decant the acid.
[Edited on 1-4-2018 by CobaltChloride]
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Chemi Pharma
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You'd better compare the use of sulfuric acid and phosphoric acid. Both are the most common fixed acids used to do this kind of job and strong enough
to deslocate other acids from their salts. Oxalic acid, in my oppinion, isn't strong and stable enough to make some acids from their metal salts,
without any kind of decomposion or byproducts formation like formic acid, CO and CO2. Oxalic acid may fail to do the job in many cases.
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