Procedure.
You will be provided with the sample of acetic acid (HOAc) in a 100 mL volumetric flask. Carefully dilute the sample to the mark with deionized water. Mix the resulting solution.
1)Pipet a 10 mL of solution into a Erlenmeyer flask. Add 3 drops of phenolphtalein and titrate with standard 0.100 M NaOH to the pink end point. Near the end point, the indicator color temporarily appears as titrant is added. When you recognize this, you should slow down the rate of addition and estimate the end point to within 1-2 drops.
2)Repeat the same titration. This time you already know the result, so you can do it more carefully.
3) Now comes the pH-metric titration. You should still add some phenolphtalein to the solution. Write pH of the solution before the addition of any NaOH. Add 2 mL of NaOH, and write the resulting pH value, the next 2 mL and so on, until you are coming as close as 2 mL to your expected end point (this is the volume you were receiving while titrating with phenolphtalein). Staarting from here, you add 0.1 mL before each reading. Detect the point when the color appears. Continue the addition at the same rate for 1 mL more, than take 2-3 readings with 2 mL steps.
4) Repeat the same pH-metric titration using methyl orange as indicator. Is the pH range of the color change the same as with phenolphtalein?

Calculations.
1. Plot the results of your potentiometric titration. The point of the highest jump of pH is your pH-metric end point. Compare it with your end point from phenolphtalein color.
2.Use your data to calculate concentration of the acetic acid in you 100 mL flask. At the equivalence point, number of moles of HOAc before titrations is exactly equal to the number of moles of NaOH you have added.
N_HOAc = N_NaOH
Number of moles of any compound in solution N_X can be written as
N_X = C_X V_X, where C_X is molarity, and V_X is volume. Thus,
C_HOAc V_HOAc = C_NaOH V_NaOH,
and C_HOAc = C_NaOH V_NaOH/ V_HOAc
3. Calculate the total amount of acetic acid in your 100 mL in grams:
m_HOAc = FW_HOAc C_HOAc V_flask (FW_HOAc = 60, V_flask = 100 mL = 0.1 L)
4. Calculate the pK of acetic acid. For doing that, use 6-8 points of your pH-metric titration before the end point.
From Henderson equation,
pH = pK + log ([OAc^-]/[HOAc])
or pK = pH + log ([HOAc]/[OAc^-]
pK = pH + log ((V_end – V)/V), where V is the volume of NaOH added at each point, and V_end is the volume of the ending point.
Average the pK values you receive.
5. From pK value you may estimate the theoretical pH of the end point.
At the theoretical point of equivalence you have only NaOAc and water.
Number of moles of NaOAc is: N = C_NaOH V_NaOH
total volume of the solution at the end point is the sum of volumes of acetic acid (10 mL volume you have pipeted) and sodium hydroxide you have added from the buret (V_NaOH). Thus, the concentration of sodium acetate at the end point is 
C_NaOAc = C_NaOH V_NaOH /(10 mL + V_NaOH)
sodium acetate is a Broensted base because it can react with a proton H⁺. For weak bases, [OH^-] = Ö K_B C.
You can calculate K_B from pK value that you have received from pH-metric titration:
K_B´K = 10^-14. Thus, K_B = 10^-14/ 10^-pK or K_B = 10^pK-14
Now you can place K_B and C into the equation above to achieve the concentartion of hydroxide OH^- at the end point.
pOH = -log[OH^-] and pH = 14-pOH
Multi step calculations from above can be done in one step using concentration C for sodium acetate at the end point and pK for acetic acid:
pH= 7+0.5´ pK+0.5´ logC
Compare your estimate for the end point with the results of calculations.

Your results can be written in such format:

Experiment 3. 

Name _______________________ Date _____________

Volume of NaOH

Titration No.1 _______ mL
Titration No.2 _______ mL
Titration No.3 _______ mL
Titration No.4 _______ mL

Average _________ mL   Standard deviation _________ This is your Vend (see table below)

Concentration of acetic acid _____________

Mass of acetic acid in the flask___________

pH-metric titration