Titration Experiment

Background Information: Phenolphthalein (phen) is an indicator that is colorless in an acid and bright pink in a base.

Purpose: To determine the molarity of three acids – citric acid, vinegar, and soda.

Hypothesis: Before you begin the experiment, hypothesize. Predict which substance will have the highest molarity? The lowest?

Procedure:

Add 10 drops of acid to a clean, rinsed cup. Add 1 drop of phen, the indicator.
Add 0.1 M NaOH, drop by drop to the acid until the color turns pink.
Record the number of drops of NaOH needed to reach neutralization.
Rinse and dry the cup before going onto the next trial.

If time allows, repeat each experiment twice.

Data:

Number of drops of 0.10 M NaOH

Trial #1

Trial #2

10 drops of citric acid

10 drops of vinegar

10 drops of soda

The balanced equations for the reactions:

Citric acid: H₃C₆H₅O₇ + 3 NaOH 3 H₂O + Na(C₆H₅O₇)₃

Vinegar: HC₂H₃O₂ + 1 NaOH H₂O + NaC₂H₃O₂

Soda: H₂CO₃ + 2 NaOH H₂O + Na₂CO₃

Data Analysis:

Find the molarity of each acid.

Conclusion: All three of these acids are weak, but obviously, they vary in strength. Rank them from least to most acidic.