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A buffer has a weak acid/base and its conjugate so that it can thus resist a chance in pH. You want to have large enough concentrations of both so that it can react if an acid or base is added to the solution
Hussain Chharawalla 1G wrote:If you use a weak acid or weak base, wouldn't it's conjugate be a strong base/acid? So if the buffer demands equal concentrations of weak acid and base, how would it be created?
i'm pretty sure the conjugate seesaw is only relative; if the acid is weakER then its conjugate base is strongER, etc. irl, if you have a weak acid with a conjugate base that is categorized as strong, it would actually mean the weak acid basically doesn't deprotonate. vice versa with a weak base and strong acid. HCl is a strong acid - its conjugate base Cl- ion doesn't protonate period.
it's like a spectrum
strong acid <--B---A----neutral H2O-B---A-----> strong base
a moderately weak acid/moderately weak conjugate base pairing (A and A) will fall equidistant left and right of the neutral H2O centerpoint. if a weak acid is strongER then the acid will be farther from the center and pull the conjugate base closer to the neutral center point, categorizing it as a weaker base (B and B). if an acid is so strong that it is a literal strong acid, that is it completely dissociates, then that means the conjugate base is pulled into the center point (practically) and is effectively neutral in solution/doesn't protonate more than just H2O would on its own.
this push and pull is a result of the fact that the Ka and Kb have to multiply into the Kw constant always.
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