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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(ll) sulfate; then stir.
Expected Results:
This activity demonstrates the chemical process of oxidation and reduction or a redox reaction. The color changes we observe
are attributed to different oxidation states of manganese as its reduced.
Follow up/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.
• What are the properties of transition metals?
• Name the other transition metals besides manganese. How are they different?
• Discuss how the burning of fuels, corrosion of metals, and the processes of photosynthesis and cellular respiration involve
oxidation and reduction.
Teaching notes:
• You'll get the most dramatic effect if you swirl the mixture together to combine the reactants thoroughly.
• The chart below outlines color corresponding to the various oxidation states of manganese
• Advanced students should recognize that H+ or OH– ions influence the identity of the product. They should also be able to
write the equations for the reactions.
Disposal/Clean-Up:
Remaining contents can be placed in the science department's heavy metal waste container for proper disposal.
Colors of Manganese Ions (continued)
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Beaker Oxidation State of Mn Color
1 +2 colorless
2 +6 green
3 +4 brown
4 +3 violet/rose
5 +7 purple
