Acid-Base Properties of Salts

Alternate titles:

Acid and Base Properties of Salts, Acidity of Salts

Purpose:

To show the properties of acids and bases through the use of different colors.

Materials:

• 5 display glasses

Reagents:

• 0.1 M Ammonium acetate (NH₄C₂H₃O₂)
• 0.1 M Ammonium chloride (NH₄Cl)
• 0.1 M Potassium iodide (KI)
• 0.1 M Sodium bicarbonate (NaHCO₃)
• Universal indicator

Hazards and PPE:

• Wear approved safety goggles and gloves.

Protocol:

Preparation

1. Set out the demo glasses in a line.
2. Pour 60 mL of the first solution on the first demo glass, 60 mL of the second solution into the second demo glass, and so on.

Demonstration

1. Write the following chart on the board:

   1. Color	pH
      Red	2
      Red-Orange	3
      Orange	4
      Orange-Yellow	5
      Yellow	6
      Green	7
      Green-Blue	8
      Green-Violet	9
      Violet	10

2. Add one drop of Universal indicator into each of the beakers.

Additional Notes:

• The solutions should be colored as follows:
• KI – Green (pH = 7)
• NH₄Cl – Orange (pH = 4.6)
• NaHSO₃ – Red-Orange (pH = 4.5)
• NH₄C₂H₃O₂ – Green (pH = 7)
• NaC₂H₃O₂ – Blue-Green (pH = 8.9)
• Universal indicator contains primarily thymol blue, methyl red, bromothymol blue, and phenolphthalein.
• Before adding the Universal indicator, you can have the students predict the color that each solution will change.

Disposal:

• Solutions should be put in a properly labeled waste container.
• Waste can be diluted and emptied down the drain depending on your institutions's waste protocols.

Reactions:

• Where HIn and In^- represent the protonated and unprotonated forms of the various indicators present in universal indicator:
• HIn_(aq) + AB_(aq) ⇌ HB_(aq) + KIn_(aq)

Citations:

1. This demo adapted from the demo library of the Chemistry department at the University of Illinois at Urbana-Champaign.