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What it is. This potassium permanganate solution is a 0.2 N (0.04 M) volumetric oxidizing titrant, supplied in a 1 L size. It is a deep purple solution for permanganometric titrations at a mid-range strength.
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Normality and molarity. In acid solution, permanganate is reduced from manganese(VII) to manganese(II), gaining five electrons, so its equivalent weight is one-fifth of its formula weight, 31.61. A 0.2 N solution is therefore 0.04 M, containing about 6.321 g of KMnO4 per liter (calculated).
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Its own indicator. Permanganate is intensely purple, while the manganese(II) product is nearly colorless. At the endpoint, the first excess drop turns the solution faint pink, so no separate indicator is needed.
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Titrate in sulfuric acid. Permanganate titrations are run in strong sulfuric acid. Hydrochloric and nitric acids can take part in competing redox reactions and reduce accuracy, so sulfuric acid is the standard choice.
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Standardization. Potassium permanganate is not a primary standard, so its solutions are standardized against sodium oxalate or arsenic trioxide, both available as NIST reference materials. Oxalate titrations are typically warmed to about 55 to 60 °C to speed the reaction.
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Stability. Permanganate solutions slowly decompose, a process accelerated by light, heat, organic matter, and manganese dioxide. Brown deposits indicate decomposition. Store the solution in the dark and restandardize regularly.
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What each milliliter titrates. One milliliter of 0.2 N permanganate oxidizes 0.2 milliequivalent of reductant, equal to 11.17 mg of iron(II), 3.402 mg of hydrogen peroxide, or 13.40 mg of sodium oxalate (calculated from equivalent weights).
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Why 0.2 N. A mid-range strength balances titration volume and precision for moderate reductant levels, such as iron in pharmaceutical and food samples, peroxide in cosmetic and cleaning products, and nitrite determinations.
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Calculating results. Analyte mass equals the titrant volume in milliliters multiplied by the standardized normality and by the analyte's equivalent weight in milligrams per milliequivalent. For iron(II), the equivalent weight is 55.85; for hydrogen peroxide, 17.01.
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Where it is used. Laboratories use 0.2 N permanganate for iron and hydrogen peroxide assays at moderate levels, nitrite and oxalate determinations, pharmaceutical and food QC methods that specify this strength, and teaching labs. The 1 L size suits labs with moderate titration volumes.
Technical Specifications
| Chemical Name |
Potassium permanganate, aqueous volumetric solution |
| CAS Numbers |
7722-64-7 (potassium permanganate); 7732-18-5 (water) |
| EC Number (KMnO4) |
231-760-3 |
| Synonyms |
Permanganate of potash, KMnO4 solution |
| Formula (active) |
KMnO4 |
| Formula Weight (active) |
158.03 g/mol |
| Equivalent Weight (acid solution) |
31.61 (molar = 5 x normal) |
| Concentration |
0.2 N (0.04 M) |
| KMnO4 Content |
About 6.321 g/L (calculated) |
| Titration Equivalence |
1.00 mL = 11.17 mg Fe(II), 3.402 mg H2O2, or 13.40 mg Na2C2O4 (calculated) |
| Indicator |
Self-indicating (faint pink endpoint) |
| Titration Medium |
Sulfuric acid |
| Primary Standards |
Sodium oxalate; arsenic trioxide |
| Appearance |
Deep purple liquid |
| Package Size |
1 L |
Applications / Common Uses
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Iron assays: Titrates moderate iron(II) levels.
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Peroxide products: Measures hydrogen peroxide in cosmetics and cleaners.
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Nitrite determination: Oxidizes nitrite in acid solution.
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Pharmaceutical QC: Supports methods specifying 0.2 N permanganate.
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Teaching labs: Demonstrates self-indicating redox titration.
Storage, Handling & Shipping
Store tightly closed at room temperature in a dark place, away from reducing agents, organic materials, acids, and combustibles. Light and manganese dioxide deposits speed decomposition, so protect the solution from light and restandardize periodically.
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Incompatible materials: Reducing agents, organic materials and solvents, combustibles, concentrated acids, and peroxides.
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Personal protection: Safety glasses and gloves; permanganate stains skin and surfaces brown.
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Spill response: Absorb with inert, non-combustible material; reduce residues with sodium thiosulfate or bisulfite solution before cleanup.
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First aid: Eyes: rinse with water for several minutes. Skin: wash thoroughly; brown stains fade over time.
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