Reduction of Permanganate Ion by Sulfite Ion.
Description: A sample of potassium permanganate is placed in a Petri dish and treated with aqueous hydrochloric acid. Then sodium sulfite solution is added to the mixture. The clear and deep purple solution changes to clear pale pink as the permanganate is reduced from Mn(VII) to Mn(II) during the course of the reaction.
H+
4KMnO4(aq) + 5Na2S2O3(aq) + 9H2O(l)(aq) → 4MnSO4 +10Na+(aq) + 6SO4-2(aq) + 4K+(aq) + 2Cl–(aq)
2 KMnO4 + 16 HCl + 10 Na2S2O3 → 2 MnCl2 + 5 Na2S4O6 + 10 NaCl + 2 KCl + 8 H2O
Mn(VII) +5e– → Mn(II)
S(II) – 4e– → S(VI)
Source: UW-Madison Card Catalog
Year: N/A Vol: N/A Page: N/A
Keywords: Reduction, Permanganate, Sulfate, Sulfite, Oxidation, Acid catalysis
Rating: 
Hazards: Some
- Acute toxicity hazard- oral
- Skin corrosion hazard
- Corrosive to metals
- Serious eye damage
- Long-term (chronic) aquatic toxicity hazard
- Short-term (acute) aquatic toxicity hazard
- Oxidizing solids
- Specific target organ toxicity- respiratory hazard, brain
- Electric shock hazard
Effectiveness: Good
- Results are observable without guidance
- Good connection from demo to course material
- Contrast in systems behavior is clear
- Time to results is low
- Good reliability
Difficulty: Low
- Simple manipulations for most to perform
- Demos at standard conditions
- Simple procedures
- Use of mildly reactive substances
Safety Precautions:
- Eye protection required
- Gloves required
- Avoid exposure to mists, droplets, dusts, or vapors
- Perform in a well-ventilated area
- Use UL approved three-prong plug and outlet
Class: Redox Reactions, Transition Metals and Coordination Compounds
Division: Inorganic Chemistry , General Chemistry
Home| Inorganic Chemistry Demonstrations| General Chemistry Division