1. Approximately 0.250 grams of the unknown acid was weighed and added to the beaker, along with 50 mL of water and 1 drop of phenophthalein.
2. Standardized sodium hydroxide (NaOH) was titrated into the solution, the changes in pH were recorded, more data points were recorded, smaller volumes were added, as the rate of change increased.
3. The data was plotted, the first derivative was calculated and plotted, and the equivalence point and pKa values were determined graphically.  The EW was calculated.

Pre-Lab Questions:
(The web master makes no claims as to the correctness of the following answers)

1. Calculate the pH and pOH of a 1.0 x 10^-5 M solution of HCl?
 

HCl is a strong acid, so [HCl] = [H3O+] = 1.0 x 10-5 pH = -log [H3O+] = -log (1.0 x 10-5) = 5 Kw = [H3O+][OH-] = 1.0 x 10-14 Kw / [H3O+] = [OH-] = 1.0 x 10-14 / 1.0 x 10-5 = 1 x 10-9
pOH = -log [OH-] = -log (1 x 10-9) = 9 pH = 14 - pOH = 5

2. What is the pH of a buffer prepared by mixing 15 mL each of 0.10 M acetic acid and 0.10 M sodium acetate (K_a = 1.75 x 10^-5)?
 

pH = pKa + log [A-]/[HA] pH = -log (1.75 x 10-5) + log (.10/.10)
pH = pKa =  4.76

3. Calculate the pH of 0.100 M Na₃PO₄ solution (K₃ = 7.1 x 10^-13)?
 

K3 = 7.1 x 10-13 = [BH+][OH-]/[B] = x2 / .100 – x  x2 =7.1 x 10-13 x 0.1 = [BH+][OH-] x = 2.66 x 10-7 = [OH-] Kw = 1 x 10-14  = [H3O+][OH-] [H3O+] = 3.75 x 10-8
pH = -log [H3O+] = 7.43

4. The following data were obtained for the titration of 500 uL of 0.10 M acetic acid with 0.10 M NaOH.
Plot the titration curve and first derivative curve on a sheet of graph (EXCEL) paper.  Determine the equivalence point of the titration and find the Ka of acetic acid.

See attached.