Acid-Base Titration

Purpose:

  1. To determine the molarity of an unknown acid solution by titration using phenolphthalein as an indicator.

Materials:

  1. Burets
  2. Clamp
  3. Stand
  4. Beakers
  5. 1M HCl solution
  6. 1M NaOH solution
  7. Unknown HCl solution
  8. Phenolphthalein indicator solution

Procedure:

  1. Clean and dry the burets and beaker, and clamp the two burets to the ring stand. Fill one of the two burets with 1M HCl solution, and the other with the NaOH solution.
  2. Use the buret to measure out 20 mL of HCl into an empty beaker. Add 2-3 drops of the indicator solution.
  3. Titrate slowly with the NaOH solution, with constant swirling, until one single drop of NaOH causes a permanent pink color that does not fade onswirling. Record the volume of NaOH used.
  4. Use the formula M1V1=M2V2 to determine the concentration of the NaOH solution. This solution may now be used to titrate the unknown acid sample.
  5. Replace the buret containing the 1M HCl with the buret containing the HCl solution of unknown concentration. Refill the NaOH buret, and wash out the beaker.
  6. Repeat the titration from steps 2-4 using 20 mL of the unknown acid solution to determine the concentration of the HCl solution.


Data & Information

Titration #1
Volume HCl used 20 mL
Concentration HCL used 1M
Volume NaOH used mL
Concentration NaOH used M
Titration #2
Volume HCl used 20 mL
Concentration HCL used M
Volume NaOH used mL
Concentration NaOH used M


Questions:

  1. What was the pH at equivalence point for this titration?
  2. What is an indicator? Why was phenolphthalein used as an indicator for this titration?