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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: 113zami on August 15, 2008, 07:24:09 PM

Title: buffer and adding base
Post by: 113zami on August 15, 2008, 07:24:09 PM

 I know that when OH ions are added to a weak acid buffer they will combine with the weak acid and more H+ ions will be released into solution  as a result, but how does that happen equation wise??  ie. if this is the weak acid buffer equation (before OH addition):

HA ---> H+  +  A-

and this is the equation after you add the OH ions

HA  +  OH  --->  A-  +  H2O

there are no H+ ions in the above equation, so where are these H+ ions that should be released into solution after the OH addition coming from??

Title: Re: buffer and adding base
Post by: Astrokel on August 16, 2008, 02:04:18 AM

hey!

Weak acid buffer consist of a weak acid, HA and a salt of the acid's conjugate base, NaA.

HA(aq) <----> H+ + A-

NaA ----> Na+ + A-

Due to the dissociation of NaA, there will be large reservoir of A-, this shifts equilibrium of the acid dissociation to the left. So at equilibrium, there will be large reversoir of HA acid, A-(from the salt), little amount of H+, from what i heard the equilibrium to the left shifts up to 97%, so H+ is almost negligible, even if it does reacts with the OH-, it will form H2O, but probably only a small amount.