Detection of Ions in Solutions Using Acid/Base Chemistry: A Quality Control Test

Objective: This lab focuses on the detection of ions using titration as an analysis tool. You will standardize NaOH and HCl solutions so that you know the exact concentration and then prepare samples of common household items in order to determine the amount of calcium in Tang®, Mg(OH)2 in Milk of Magnesia, etc. You will learn to prepare samples of a specified concentration, learn about acids and bases through the use of titrations and learn how to detect endpoints using different indicators. You will become adept at measuring pH with both a pH meter and indicator paper. You will then conduct quality control testers and determine if the label on a
4. Report the concentration of NaOH to the class. An average number will be determined to give the most reliable value of NaOH concentration. Do not discard the remaining NaOH – you will use this for the rest of these experiments.
Standardizing an HCl Solution

In a titration, it is critical to know the exact concentration of the titrant (the solution in the buret which will be added to the unknown) in order to determine the concentration of solutions being tested. We will standardize the ~0.1 M HCl solution (the titrant) with sodium carbonate (Na2CO3) using phenolphthalein as the indicator. Na2CO3 is a base and reacts with the strong acid HCl in the following way:

To Standardize:

1. Weigh ~0.2 g Na2CO3 into an Erlenmeyer flask and dissolve it in 50 mL of boiled, cooled distilled water. Record the exact amount of Na2CO3 used in your notebook. (The water is boiled to expel CO2 from the solution.)
2. Add 4 drops of phenolphthalein to the solution and record the color.
3. Titrate with the HCl until just before the endpoint (when the solution is very light pink) and then gently boil the solution to expel the CO2 from solution that has been produced during the reaction (see eq 4).
4. Cool the solution to room temperature and then wash the sides of the flask with a small amount of H2O to