Sciencemadness Discussion Board

calculating Solubility

Broken Gears - 5-2-2006 at 15:05

Searching in this Forum and on Google did not make me smarter. I just dont get it.
Im trying to calculate how acetone(58,08g/mol) is needed to disslove 10grams for acetylsalicylic acid(180,154g/mol).

Can someone explain how to calculate this in easy-understandable-way?

[Edited on 5-2-2006 by Broken Gears]

12AX7 - 5-2-2006 at 16:12

Incidentially, I don't think you can, without looking up empirical solubility data.

Is there actually a relatively easy way to calculate solubilities and such of various chemicals?


DeAdFX - 6-2-2006 at 15:00

I think there is only one thing that one can do to determine solubility... Nitrates/ammonia compounds/sodium/potassium/chlorates/perchlorates etc are solubile.

Doesn't give number values but at least you know if something is solbuble...

12AX7 - 6-2-2006 at 18:27

Originally posted by DeAdFX
potassium/chlorates/perchlorates etc are solubile.

Except these two last combinations, and potassium hexanitritocobaltate I think it is.

Sodium bicarbonate is relatively insoluble, too.

That's the problem with rules in chemistry, you can't make any generalizations!


woelen - 6-2-2006 at 23:36

Originally posted by 12AX7... and potassium hexanitritocobaltate I think it is....

Yes, it really is insoluble, I was very surprised to see a potassium salt, which is so much insoluble. Also really insoluble is the bright orange K2PdCl6, which can be made by heating a solution of PdCl2 in dilute HCl with a solution of K2S2O8.

Another highly insoluble alkali metal compound, I've come across is Na3[IO4(OH)2]. This can be prepared by adding a calculated amount of NaOH-solution to a solution of NaIO4 in water. A white flocculent precipitate is formed at once.

General Solubility Rules(in water)

MadHatter - 7-2-2006 at 10:35

The Solubility Table

Rules and Exceptions

1. All nitrate (NO3¯), nitrite (NO2¯), chlorate (ClO3¯) and perchlorate (ClO4¯) salts are
soluble. Silver nitrite and potassium perchlorate are considered slightly soluble.

2. Essentially, all alkali metal (Li+, Na+, K+, Rb+, Cs+) and ammonium (NH4+) salts are
Exceptions: rare

3. Most halogen (Cl¯, Br¯, I¯) salts are soluble.
Exceptions: Ag+, Pb2+, Hg2+,Cu+, Tl+ (Pb2+ halogens are soluble in hot water.)
HgBr2 is slightly soluble.

4. Most acetate (C2H3O2¯) salts are soluble.
Exceptions: Ag+, Hg2+

5. Most sulfate (SO42¯) salts are soluble.
Exceptions: Ca2+, Sr2+, Ba2+, Ra2+, Pb2+, Ag+, Hg2+ (Some sources consider calcium
sulfate and silver sulfate to be slightly soluble.)

6. Many sulfides (S2¯) are insoluble.
Exceptions: All alkali metal and alkaline earth (Be2+, Mg2+, Ca2+, Sr2+, Ba2+, Ra2+) sulfides
are soluble. Ammonium sulfide is soluble. (Some sources consider MgS, CaS and BaS to
be slightly soluble.)

7. Most borates (BO32¯), carbonates (CO32¯), chromates (CrO42¯), phosphates (PO43¯),
and sulfites (SO32¯) are slightly soluble. MgCrO4 is soluble, MgSO3 is slightly soluble.

8. Most hydroxide (OH¯) salts are insoluble.
Exceptions: Alkali metal hydroxides are soluble. Ba2+, Sr2+, Ca2+, Tl+ are considered
slightly soluble.

These are some general rules. There will always be exceptions to any set of rules.

[Edited on 7-2-2006 by MadHatter]

unionised - 7-2-2006 at 13:52

This discussion is all very well, but it fails to address the original question which was about organics. Though, while we are on the subject, what about the low solubility of sodium dizinc di uranyl acetate (and the magnesium equivalent) and the relatively interesting compound Cr(II) acetate?

You might get somewhere looking at the "ideal solubillity" which is calculable but
1 is usually wrong and
2 needs you to know the heat of fusion of the material.

I'm afraid it's usually a matter of experimentation. There are some vague rules for solubility among the organics based on the idea that "like disolves like".

daeron - 7-2-2006 at 15:29

the answer to the question-how to calculate the solubility of an substance in an another substance:
you have to start with a good EOS model for both substances, i think SRK will work fine for these, derive all the needed props, find the K values, the pfitzer coeffs,...etc,etc... and after that a lot of playing around with gibbs energies of mixing and whatnot...and the outcome is not 100% correct..

if one would really start from scratch id consider that a real ordeal..
it is certanly possible but im thinking since you already dont know this, you probably dont need to go so far...

probably youre better off finding some empirical data