Chemical Forums
Chemistry Forums for Students => Physical Chemistry Forum => Topic started by: Darwin on January 07, 2010, 12:23:22 PM
-
Hi
I have a question that has bothered me for long now, and I can't really find an answer. For an e.g. HCl(aq) solution, is the following relation true?
aHCl2 = aH+*aCl-
or should it rather be aHCl = aH+*aCl-?
where a is the activity.
-
Hi
I have a question that has bothered me for long now, and I can't really find an answer. For an e.g. HCl(aq) solution, is the following relation true?
aHCl2 = aH+*aCl-
or should it rather be aHCl = aH+*aCl-?
where a is the activity.
What seems logical to you and why?
-
What seems logical to you and why?
Well, normally for a reaction like HCl :rarrow: H+ + Cl-, we write [HCl(aq)] = [H+] = [Cl-], so [HCl]2 = [H+][Cl-], and the exact same thing with molalities. So my logical answer is that aHCl2 = aH+aCl-. However, in a standard solution book that I have, it is indicated that aHCl = aH+aCl-, though without any concomitant explanation. I'm wondering if that's wrong..
-
I am not aware what aHCl is, unless it is activity of dissolved but undissociated HCl, similarly to - say - aCH3COOH - activity of undissociated acetic acid. Usually we assume activity of uncharged species is just their concentration (activity coefficient is 1).
-
Well, normally for a reaction like HCl :rarrow: H+ + Cl-, we write [HCl(aq)] = [H+] = [Cl-], so [HCl]2 = [H+][Cl-], and the exact same thing with molalities. So my logical answer is that aHCl2 = aH+aCl-.
Why do think it is [HCl]2 ?