Purpose
To illustrate the various oxidation states of an element.

Materials

• Potassium permanganate, KMnO4 (0.1 M)
• Sodium hydroxide, NaOH (2.0 M)
• Sulfuric acid, H2SO4 (3.0 M)
• Sodium bisulfite, NaHSO3 (0.1 M)
• EDTA (1.0 M)
• Manganese(II) sulfate, MnSO4 (powder)
• 5 ea. 100 mL beakers
• 50 mL graduated cylinder

Safety

• Read the MSDS/WHMIS sheets for all chemicals before using them
• Wear chemical safety glasses, gloves, and lab coat
• Concentrated acids and bases are used
• Permanganate solution will stain

Procedure

1. Pour 50 mL of 0.1 M potassium permanganate in five 100 mL beakers (labeled 1 to 5).
2. To beaker number 1 add 15 mL of 3.0 M sulfuric acid and then while stirring slowly add 0.1 M sodium bisulfite until a color change takes place.
3. To beaker number 2 add 20 mL of 2.0 M sodium hydroxide and then while stirring slowly add 0.1 M sodium bisulfite until a color change takes place.
4. To beaker number 3 slowly add 0.1 M sodium bisulfite while stirring until a color change takes place.
5. To beaker number 4 add 5 mL of 1.0 M EDTA and a pinch of solid manganese(II) sulfate then stir.

Follow-up Teaching Notes
The chart below outlines color corresponding to the various oxidation states of manganese:

Concepts
Oxidation states, balancing redox equations.

Extension

• Students can be asked to write balanced equations for beakers 1, 2, and 3 if they are told the oxidation half-reaction is HSO₃^-1 -> SO₄^-2
• The reduction half-reaction is MnO₄^-1 -> Mn^? where the ? refers to the oxidation state of manganese in the appropriate beaker.

Disposal/Clean-up
Remaining contents can be placed in the science department’s heavy metal waste container for proper disposal.

Activity provided by ScholAR Chemistry.

See Ward’s for more chemistry demonstrations and activities.

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