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

2748 Words Aug 24th, 2014 11 Pages
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
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To calibrate the pH meter:

1. Remove the electrode from the distilled water and place it in pH 4 buffer, which is pink. Make sure the electrode is completely covered in buffer and swirl the solution around.
2. Set the pH meter to pH 4 and then rinse the electrode with distilled water to remove any excess solution.
3. Place the electrode in pH 10 buffer (which is blue) and swirl it around in the solution.
4. Set the pH meter to pH 10 and rinse the electrode, returning it to the distilled water once you are finished.

The pH meter should now be calibrated to measure any pH accurately.

Standardizing a Sodium Hydroxide (NaOH) 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 the solution being tested. We will standardize the ~0.1 M NaOH solution (the titrant) with potassium hydrogen phthalate (KHP, KC8H4O4H) using phenolphthalein as the indicator. KHP is a weak acid and reacts with base in the following way:

To Standardize:

1. Weigh ~0.8 g of dried KHP (MW = 204.23 g/mol) into an Erlenmeyer flask and dissolve in 50-75 mL of distilled water. Record the amount of KHP and water used.
2. Add 4 drops of indicator into the flask and titrate to the first permanent appearance of pink. Near the endpoint, add the NaOH dropwise to…