[Bliz33]

sorry...may be simple but a search for this specifically would be rather difficult

predict the change to ph.....NaNO2 added to HNO2.....and HCL added to NaC2H3O2



i realize that according to le chataliers principle and the simple ionization of said compounds.....the first would increase and second would decrease
but my initial instinct for HCL added to NaC2H302 would be that it would have no effect despite the fact that HCL is a strong acid(so is NaOH....the conjugate base) and H+ ions are realeased into the solution.....ive had numerous people say no effect

stupid, yes, but id like a better explanation from someone that has a much better understanding

[nj_bartel]

http://www.science.uwaterloo.ca/~cchieh/cact/c123/conjugat.html
http://www.science.uwaterloo.ca/~cchieh/cact/c123/baseacid.html
http://en.wikipedia.org/wiki/Acetic_acid     <=First Paragraph

I believe there is a result.  If there is, your answer lies in those links as to why there is.  If there is not a result, an admin will correct me (believe the admin, I'm a little hazy on this).

[Borek]

You may treat both cases in a similar way - in the first case you add base (NO₂^- is a conjugated base of weak acid), in the second case you add acid. pH must change. Due to the presence of other substances in the solution change can be much smaller than if these subtances are not present - that's what we call buffering effect - but nonetheless it can be never completely eliminated and addition of acid or base always changes pH.

Le Chatelier's principle works OK for this case, although you can get quantitative results (i.e. calculate exact pH change) using so called Henderson-Hasselbalch equation and assuming, that added acid (or base) reacted stoichiometrically (i.e. to the end) with the substances present in the solution.

[Rabn]

Qualitatively speaking Le Chatliers principle will send you in the right direction.  In the first case you have HNO2 -> (H+) + (NO2-) adding (NO2-) pushes the equilibrium backwards and the pH will increase.  Good instincts there.  In the second case you need to really consider the components of the solution.  Initially you have Na(acetate) which when added to water you get (Na+) + (actetate) + H2O -> (Na+) + H(acetate) + (OH-) so the solution is initially basic as defined by its pKb. When you add HCl it completely dissociates.  The first thing that happens is the (H+) will neutralize any (OH-) present which drives the formation of acetate. The excess (H+) will then protonate acetate ions until there are no more available or all of the acetate ions have been protonated(This is the buffering effect that Borek spoke of). Any left over (H+) or acetate molecules that react with water to form (OH-) will define the pH. Regardless of how much HCl is added the pH will be reduced, making your initial instinct incorrect.  What caused you to have that instinct? I'm curious as to why multiple people thought the pH would not be effected.

[nj_bartel]

Can't believe I didn't immediately recognize the buffer.