Chemtastic - 1-7-2004 at 14:47
I know virtually every source you might come across say that strong acids completely dissociate and thus have an acid dissociation constant of
infinity. I just can't imagine, though, that there isn't any non-dissociated HCl, HBr, HI, HClO3, HClO4, HNO3, or H2SO4 in a solution of
each compound. The acid dissociation constants could be extremely high, but if some REALLY weak acids have reported contstants of 10^-15, why
aren't strong acids reported at, say 10^15? There must be some way to measure it.
Also, why are the solubility products of relatively soluble salts never reported? Murcury compounds will have a reported solubility product of
10^-55, but they never list NaCl's Ksp as 28 (what it should be, giving it's molar solubility).
Is there some fact that I'm overlooking, or am I just more anal about this than the rest of the chemical world
?
t_Pyro - 1-7-2004 at 19:10
The dissociation constants of stong electrolytes are axtremely high, so for all practical purposes (including theoretical calculations), one can
assume them to be completely dissociated. Indeed, one could quantify their values, but they would be of no use to you for two reasons:
1. Firstly, apart from academic interest, you wouldn't have gained anything.
2. At extremely high concentrations (where the dissociation constant becomes important to be considered), the activity of the species will not be the
same as their molarities. I'm not sure how to calculate the activity of species under such circumstances.
unionised - 3-7-2004 at 06:47
As you say, there is at least some fre HCl in hydrochloridc acid, thats why it smells. Some of the undissociated HCl evaporates.
Most of the time people work with solutions in water and any acid that is strong enough to protonate water (ie to frm H3O+ ions) is as strong as any
other.
If you start working in other solvents you can have much stronger acids, their strengths are measured by a property called the Hammett function.
Feel free to Google it.