Can HCl replace H2SO4 in the reaction used to produce phosphoric acid from bone ash (Ca3(PO4)2)?
I'm having trouble finding sulfuric acid OTC besides the dilute black stuff with all the buffers and stuff in it. The phosphoric acid I have found OTC
is purple with gelling agents and stuff in it.
[Edited on 16-8-2006 by Odyssèus]12AX7 - 16-8-2006 at 14:20
I don't think so, lesse the reaction works by first acidifying calcium phosphate to hydrogen, then dihydrogen phosphate (Ca(H2PO4)2), which then is
more soluble than CaSO4, which precipitates in turn. And the higher (insoluble) calcium phosphates aren't formed, because the pH is too low.
HCl would form CaCl2, which is very soluble. The best you could do, then, is an acidic solution of Ca(2+), H2PO4- and/or H3PO4, and H+ and Cl-.
Evaporation will do no good, as H3PO4 doesn't boil, while HCl will evaporate quite nicely. You may be left with something like CaCl2 and Ca(H2PO4)2
in crystalline form. Fractional crystallization may seperate the phosphate, but I don't see you ever getting more than H2PO4- with HCl.
Note that, although H2SO4 is stronger than H3PO4, on heating the H2SO4 will ultimately decompose/boil off, leaving H3PO4 (which itself dehydrates some
on extensive heating). The same goes for H3BO3 and H2SiO3/H4SiO4, which also form glassy melts and dehydrate towards the anhydride.
TimOdyssèus - 18-8-2006 at 08:10
I guess I'll have to stick with my purple goop. That is unless I get the lead chamber process to work for me.
Thanks for clarifying the reaction for me.not_important - 18-8-2006 at 09:07
What is the intended use of the H3PO4? If it is for making phosphorus, go with either. Organic additives will get burnt out early, most of the rest
will be harmless.Odyssèus - 18-8-2006 at 10:24
That and preparing various phosphates and phosphorus salts.12AX7 - 18-8-2006 at 14:27
Well then, hmm you could add, say, Na2SO4 to the acid calcium product, giving something like:
Na2SO4 + Ca(H2PO4)2 > 2NaH2PO4(aq) + CaSO4(s)
That ought to work... then filter, crystallize and go with metathesis reactions (sodium phosphate ought to be pretty soluble, huh?).
Tim
Interesting point
chloric1 - 18-8-2006 at 18:05
The still available trisodium phosphate may be a better choice. In aqueous solutions this slat actually forms NaOH and disodium phosphate. The OTC
is the dodecahydrate so you should calcinate the water of hydration off first before making your solution. If you add the calculated amount of HCl
just to neutralize the NaOH then you will be left with disodium phosphate and NaCl. The interesting point here is NaCl has realtively constant
solubility at various temperatures while disodium phosphate varies greatly in solubility at various temperatures. You should be able to separate the
later. ONce more the solubility in cold water is quite low so a second recrystalization from distilled water will remove more impurites.Odyssèus - 18-8-2006 at 19:36
I have found trisodium phosphate at my local hardware store but it is expensive and cut with something (only about ~15% pure). Thanks for the advice
though!
[Edited on 19-8-2006 by Odyssèus]not_important - 18-8-2006 at 23:57
Odd,all the TSP I've seen is the plain dodecahydrate stuff.
I was going to suggest the same as chloric1, use TSP for making phosphates, calcium phosphate and acid for when the target is phosphorus.
When I needed a bit of clean H3PO4, I used a similar method. I gassed a hot solution of TSB with HCl, and allowed it to cool while still being treated
with more HCl. When it was fair cool, I filtered it off from the NaCl formed. I evaporated it a bit, then added a lot of isopropanol which
precipitated most of the rest of the salt. After that add water, distill the alcohol off, then the water, then excess HCl. After that I followed a
procedure for getting solid H3PO4: heat to a bit higher temperature-that-I-can't-remember, cool, set aside for awhile, remove the H3PO4 crystals.
But that's a lot of work, as many phosphates are not very soluble you can just add T SP or partially neutralised TSP to a solution of the desired
cation; the NaCl or Na2SO4 from the neutralisation just stays in solution out of the way.YT2095 - 19-8-2006 at 02:47
H3PO4 crystals?
can you describe them to me please?
I ask for the simple reason that I may well have been throwing mine away considering them a contaminant
I mixed H2SO4 with CaHPO4 filtered out the CaSO4 and boiled down the liquid until it was syrupy, however very fine needle like crystals formed even
after filtering. these crystals resemble chopped up fiberglass.
another odd thing I notice it that left to stand overnight tiny bubbles start to rise slowly through the liquid from the crystal layer (inside a brown
glass bottle).Odyssèus - 19-8-2006 at 05:25
Quote:
Odd,all the TSP I've seen is the plain dodecahydrate stuff.
Can you describe where and what its used for? The stuff I found was in roughly 4 or 5cm^3 boxes used for cleaning of some kind, though as soon as I
saw it was cut then I lost interest so I cant tell you what its specific use was. It was on the shelf above the acetone, and next to the naval jelly in Lows I think.12AX7 - 19-8-2006 at 07:46
Er well, look up the properties of H3PO4 and decide. Like pure acetic acid, it has a relatively high melting point.
That formation is known as "acicular" BTW.
Timnot_important - 19-8-2006 at 08:05
TSP is used for cleaning. It appears that in the US and some other western countries pure TSP is being replaced with lo-functionality substitutes, or
mixes of TSP and sodium carbonate.
You are going to have to do research in your area, try all the different stores that stock serious cleaning products - paint stores, wood supply, the
smaller hardware stores. In the US local regulations may prevent it from being sold where you live, so you might check with friends in other areas.
Some sodium carbonate is acceptable, you just burn through more acid to get rid of it.
Another avenue is chemical suppliers that cater to candelmakers and soapmakers. One online place sells 10 pounds for less than $20. I have a huge
pail myself and I use it for cleaning my griddle especially after cooking bacon.
It was on the shelf above the acetone, and next to the naval jelly in Lows I think.