Experiment 7 -

Acetic Acid Content of Vinegar

Procedure:

Part A - Determination of Concentration of Unknown Base Solution

1. Obtain about 100 mL of base solution of unknown concentration in a clean and dry 250 mL beaker. The oven may be used to dry the beaker.
   
   
2. Acclimatize the buret by rinsing the buret with two portions of base solution of approximately 10 mL each portion. After rinsing, fill the buret to the 0.00 mL mark.
   
3. Obtain about 100 mL of standard acid solution in a clean and dry 250 mL beaker. Write down the concentration of the acid solution on the data sheet.
   
   

4. Pipet 25.00 mL of standard acid, HCl, solution into a clean 125 mL Erlenmeyer flask. (Note: the Erlenmeyer flask does not need to be dry as you will be rinsing the flask with distilled water periodically.)

   
   
   
5. Add 2-3 drops of phenolphthalein indicator to the flask.
   
   

6. Carefully add the base solution to the acid solution until the end point is reached.

   
   
7. Read the buret carefully to determine the quantity of base used to reach the end point. Record the volume of the base solution used.
   
   

   Flask #1 shows a good endpoint where the colour of the solution changes to a pale pink colour. Flask #2 shows a bright pink endpoint. The brighter colour indicates that the endpoint of this titration for flask #2 is farther away from the equivalence point than flask #1.

   
   
   
8. Repeat steps 4 to 7 until two volumes of base solution are obtained. The two volumes should agree to within 0.10 mL.