Help-Relative Concentrations During Titrations

[drtdb1]

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Hey
I had a question if someone could help me out. Its probably really simple but i always get confused.
Can someone explain the relative concentrations or ratios of the acid and conjugate base during different stages of a titration. For instance, before the titration reaches the equivalence point, at the equivalence point, and after the eq. point.



Better yet, heres the problem that got me confused in the first place.
We are doing a titration with acetic acid which has a pKa of 4.75. If the pH of the solution is at 5. Why would the amount of acid be greater than the amount of conjugate base present in the solution?

I thought that after you passed the point where the acid and the conjugate base were equal, the concentration of the conjugate base would increase compared to the amount of acid present.
When you use the Henderson-Hasselbach equation you get that .25 = log([A-]/[HA])?
im so confused here
thanks

 

[RogueUnicorn]

titrating a weak acid with a strong base (i.e. adding base to acid)

initial - LOW pH, [HA] dominates, as weak acids are not very dissociated.

as you add base:

midpoint of the flat portion: pH=pKa, and [HA]=[A]

midpoint of the vertical portion: pH>7, enough base has been added to equal the concentration of the initial [HA]

 

[Hemichordate]

We are doing a titration with acetic acid which has a pKa of 4.75. If the pH of the solution is at 5. Why would the amount of acid be greater than the amount of conjugate base present in the solution?

You got that backwards.

 

[drtdb1]

Hemichordate-
Sorry I miss stated that. I meant to say that the answer said that the acid concentration was greater than the conjugate base concentration.

Like you i thought the opposite and got the question wrong, I was just wondering why it is that we were wrong. It was a TPR question, maybe they just made a mistake.