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Effects of pH on Solubility

This demo illustrates how the solubility of a substance changes with the pH.

Materials

• 0.1 M Ferric Nitrate
• 6M Hydrochloric Acid
• 6M Ammonium Hydroxide
• Large test tube (25 x 300)
• Erlenmeyer flask (to be used as a test-tube rack)
• Lecture room sized pH meter

Procedure

1. Add about 40 ml of the ferric nitrate solution to a test tube.

2. Using the pH meter show the class the pH of the solution by dipping the electrode into the solution.

3. Add about 15 - 20 ml of 6M Ammonium Hydroxide or until precipitation occurs [Fe(OH)₃].

4. Repeat step 2.

5. Add 6M Hydrochloric Acid slowly and shake occasionally until the precipitate goes back into solution. (It should take about the same volume of hydrochloric acid as the ammonium hydroxide you used).

6. Repeat step 2.