Titration pH Confusion

[darkhope]

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Hi guys
Sorry so I'm really confused about titration and salt formation which is the same thing. Ok so basically in titration or salt formation, you get N1V1=N2V2 which makes sense because you need an equivalent amnt at equivalence point of H+ and of OH-. Yet, why are pH values different at equivalence points for weak acid/base interactions with acid/base? I get that its because of weak acid/base forming conjugates which don't form in strong acid/base. But I don't get the role of conjugates in affecting pH? Because given N1V1=N2V2, then H+ must equal OH- in terms of amount so why is it that [H+] does not equal [OH-] at equivalence point? I'm definetely missing something and am so confused... Basically why isn't pH=pOH=7 at equivalence point since there is an equal moles of H+ and OH- at equivalence point and the volume of the solution will be the same, so why isn't the molarity of H+ and OH- the same at equivalence point? please help...thanks...

 

[darkhope]

Hey guys, thanks, i think I finally got it.

 

[hvairline]

You have to understand that the salts formed during a titration can act themselves as acids or bases thus affecting the ph. This does not occur with strong acids/strong bases titrations because the salts contain the conjugates of them and are thus very weak.Thus in such an instance we have [OH-]=[H+] but in no other

 

[whiteshadodw]

strong base/acid titration = super weak base or acid leftover, disregard
weak acid/base titration = weak base or acid leftover, cannot disregard the effect of the conjugate. also, the weak acid/base concentration at the beginning of the titration is equal to the conjugate concentration at equivalence.