FGP - 25-3-2005 at 04:32
Would potassium bisulphate dissolve in conc. sulphuric acid?
Assuming it does would this increase the density and thus become a convenient adulterant?
I have some vague evidence that this was done in the early days of manufacturing (before analysis) but would appreciate a modern chemical point of
view.
Thanks.
FGP
BromicAcid - 25-3-2005 at 19:00
What do you mean by adulterant (I see the word as just generally meaning additive) what do you hope to accomplish by dissolving potassium bisulfate in
H2SO4?
adulteration of acid.
FGP - 26-3-2005 at 03:00
The 'evidence' is that in the early 1800s potassium bisulphate was added to sulphuric acid in order to increase the density and therefore
the price at which it could be sold.
My task is to show that this practice was viable both technically and commercially.
I need some opinions of present day chemists.
Thanks.
sparkgap - 27-3-2005 at 08:54
Let's see... I will try to understand... you will be mixing a strong acid and its insanely weak conjugate base for the purpose of selling the
stuff claiming it to be the pure acid itself... (why else would you want to increase density?)
I'll let the others lecture about ethics...
sparky (^_^)
P.S. Oh, in case you haven't figured it out yet, you're going to have a neutralization of sorts mixing them. Have fun with the bubbles!!!
Nicodem - 27-3-2005 at 09:26
OK, I guess what works for sodium bisulphate works with potassium bisulphate as well, hence this reply…
Dissolving sodium pyrosulphate (Na2S2O7) in concentrated sulphuric acid gives oleum (SO3 in H2SO4) and sodium sulphate (Na2SO4):
Na2S2O7 + H2SO4 ==> Na2SO4 + H2S2O7 (= H2SO4 + SO3)
I don't know however if the Na2SO4 remains dissolved or not. This is described in a patent as a method of preparing oleum and was already posted
to another legendary forum. Unfortunately I don't remember the patent number and don't fell like searching for it.
[edit: This post is not really related to the original question of this thread since I confused the bisulphate with the pyrosulphate. The mistake has
been corrected. Thanks to Sparky for noting it.]
[Edited on 27-3-2005 by Nicodem]
sparkgap - 27-3-2005 at 09:30
I am now thoroughly confused 
.
Isn't bisulfate ion HSO<sub>4</sub><sup>-</sup>?
sparky (°_°)
Nicodem - 27-3-2005 at 09:52
Hm... sorry, my mistake.
Yes, potassium bisulphate is KHSO4. I got confused as I saw no reason on why someone would want to add it in H2OS4, so I automaticaly mistaken it for
the pyrosulphate as I remembered it can be used to increase the concentration of H2SO4 even "above" 100%.
But FGP, what is this "adulteration" thing then if it is not about increasing concentration (density)?
mick - 27-3-2005 at 10:30
Is this just about scams people have done in the past like ethylene glycol in wine, to pass of a low grade product as something better. I would have
thought KHSO4 would be more soluble than the sodium salt in strong H2SO4 since all the anions present could solvate the potassium better. A bit like
dissolving KOH in water.
It might have been used to increase the density reading for spot sales but I would have thought it should have been clocked by regular buyers. A
simple flame test or something would indicate serious contamination.
mick
Testing for adulterants
Kinetic - 27-3-2005 at 12:51
I don't know whether potassium bisulfate is soluble in sulfuric acid or not, so I can't comment on the viability of the proposal.
Still, I'm surprised nobody has mentioned titration yet. Surely, even back in the early 19th century, this would be one of the (few) standard
methods of analysis. A simple base titration of the offending 'concentrated sulfuric acid' would immediately give a result inconsistent with
that expected.
I'm sure that even today, similar practices are carried out to increase the profit margin in selling chemicals, though these are probably more
likely to be due to laziness in purification rather than deliberate adulteration. Do not assume that these methods were performed only because they
were undetectable. As mick points out, it is more likely that they were carried out - and got away with - only because the majority were not thorough
enough to check for any additive.