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National Chemistry Week - Experiments - Make Your Own pH-Indicator
Objective:
To make a phenolphthalein indicator and test the acidity or basicity of household products. Phenolphthalein is a large organic molecule which is a weak acid. It changes colour depending on whether the solution is acidic or basic. Each pH indicator has a pH range in which it will change colour. For phenolphthalein, this range is 8.3 - 10.0. This means that at or below pH 8.3 the colour will be colouriess and at or above pH 10.0 the colour will be pink. Testing pHs below pH 8.3 can be done with other indica- tors such as litmus. Litmus has a pH range of 4.4 - 8.3. At pH or below 4.4 it is red and at or above pH 8.3 it is blue.

Materials:

  • glass jars
  • labels
  • dropper
  • mngspoons
  • H20 (water)
  • wax paper
  • Ex-Lax tablets (2)**
  • 2-propanol (rubbing alcohol)
  • hammer or heavy blunt object
  • household products (e.g. baking soda, washing soda, cleaners, antiseptics, etc.)

Procedure:

  1. Prepare the phonolphthalein indicator as follows:
    1. Smash the tablets while wrapped in wax paper.
    2. Add 30 mL of 2-propanol to the jar.
    3. Add the powdered tablets to the jar and stir (may not fully dissolve).
  2. Prepare aqueous solutions of household products.
  3. Add 2-3 drops of the phenolphthalein indicator until colour change occurs (if the pH of the solution is below about 8, colour change will not occur).
logo** phenolphthalein is no longer found in Ex-Lax due to its cancer causing test results.  It was at the time this experiment was published.