[GeLe5000]

Good evening.

I've just dissolved 0,125 g Acetylsalicylic acid in 100 ml of a phosphate buffer, pH 7,3 at 20°C.
According to Wikipedia, it's the solubility limit in water at 15°C.

I was astonished by the time necessary to dissolve this substance : 10 hours or so, with a mixing of a few seconds every hour.

I suppose that if I could grind the crystals to a sub-nanoscopic powder, the dissolving could be instantateous, because it's a matter of activation energy. If the molecules are all separated, water molecules will have no more work to do. But am I right ?

Another question : do we know how salts in a solution can influence the dissolving of an organic molecule ? Can you predict that that the dissolving of Acetylsalicylic acid in distilled water would be faster than in a phosphate buffer ?

Thank you.

[Enthalpy]

Grinding is a good start, not to reduce the a work, and I'd say not because of some activation energy, but to help the diffusion of the solute in the solvent.

Stirring too is a good idea for the same reason: help the diiffusion.

That's why you get sugar as porous dices nowadays instead of a loaf and stir the coffee.