[ebonized]

Attempting to do my formal lab calculations for a lab report due on Monday, but running into problems as the manual is relatively unclear, and I'm not sure where to start. I'll briefly explain how the lab went and the values I had found.

-trying to determine the Ka value of the unknown acid, which could be acetic acid or its three chloro substituted derivatives (monochloroacetic acid, etc)

[NaOH] = 0.10002 M
Volume at equivalence point: 24.685 mLpH at equivalence point: 9.47

pH meter error : +/- 0.01 instrument error
25 mL pipette error: +/- 0.5 instrument and reading error
50 mL burette error: +/- 0.02 instrument and reading error
(need to do error calculations for the steps that involve these values)

need to:
-calculate the concentration of the unknown acid
-calculate the Ka of the unknown acid from the data at the 0%, 20%, 40%, 60%, 80% and 100% titration points (where 100% is the equiv. point)

We're supposed to do this with simultaneous equations, however they confuse me and I'm not sure exactly what I'm trying to find with the equations.


Thanks for all the help, it's much appreciated.

[UG]

[NaOH] = 0.10002 M
Volume at equivalence point: 24.685 mL
pH at equivalence point: 9.47

Is that the total volume or the amount of NaOH added?

[ebonized]

[NaOH] = 0.10002 M
Volume at equivalence point: 24.685 mL
pH at equivalence point: 9.47

Is that the total volume or the amount of NaOH added?

It's the total amount of NaOH added

[UG]

And how much acid did you start off with?
Knowing all this, you have enough information to
-calculate the concentration of the unknown acid

[ebonized]

25 mL of acid. What else do you need to calculative the different percentages?

[Borek]

As this is monoprotic acid situation is simple - 20% means 0.2*24.685 mL.

[ebonized]

I get that part...what about the rest of it? Ka? What do I do with the percentage values? I need someone to go t hrough this step by step

[Borek]

Assume neutralization was quantitative - that'll give you ratio of HA/A^-, then use Henderson-Hasselbalch equation.