Question

need help with that and how to do the graph please

342 Report Sheet . Determination Determination of the Dissociatia Constant of Weak Acid C. Determination of pk of Unknown Acid First determination ml NaOH pH 3.11 Second determination ml NaOH pH 3.56 Third determination ml NaOH pH 405 4,23 -4.10 darm544941117111 4.57 4.66 al 4,86 4.10 5.10 Alamagn 111111 to. 44 10.45 10,33 10. ut باميل 10.50 Volume at equivalence point Volume at one-half equivalence point pK, 4. K pka Standard deviation of Average K, (show calculations)

Answer 1

For the graphic, you need to plot the pH as a function of the added volume of NaOH. I usually use Excel for this, but I'm having problems with it now, but the graph should look like this:

Trial 1:

Hd 10 Vol NaOH

Trial 2:

Hd 10 Vol NaOH

The point of maximum growth of the curve (that is, when it is the most steep) is the equivalence point of the titration. In this cases, this happens between 14 and 15 mL, where the pH "jumps" around 4 units. So, given this data, we can say that the equivalence point is at 14.5 mL of NaOH. Since the pH midway to the endpoint represents the pKa of the acid being titrated, we can determine it this way. The volume halfway to the endpoint would be half the volume of the endpoint, that is: 7.25 mL. We don't have a point at that value exactly, but we can approximate it by the point at 7 mL (since pH does not change that much around those values). The pH when 7 mL of NaOH had been added was: 4.57 for trial 1 and 4.74 for trial 2. These are the obtained values of pKa for each trial which can be then, for example, averaged, to give an average value of 4.66.