Determination of reduced potassium permanganate substances (2)

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Avoid direct exposure of the test solution to strong sunlight during the test

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Under specified conditions, in an acidic medium, the sample reacts with excess potassium permanganate melt, and the amount of remaining potassium permanganate is determined by iodometry

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1 Sulfuric acid solution: 1+37
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2 Potassium permanganate solution: 1g/L
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3 Potassium iodide solution: 100g/L
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4 Sodium thiosulfate standard titration solution: c(Na ₂ S ₂ O ₃ )=0.
05mol/L
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5 Starch indicator solution: 10g/L
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3 Apparatus

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1 Low temperature and constant temperature water bath: The temperature can be controlled at (20±0.
5)℃
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4 Analysis steps

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1 Take a sample according to the product standard, place it in an iodine measuring flask containing 50 mL of sulfuric acid solution, and mix well
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Immerse the iodine flask in a water bath controlled at (20±0.
5)℃, keep it for 15 minutes, add potassium permanganate solution with a burette until the color does not fade, then add (10±0.
05) mL potassium permanganate solution
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Record the total volume of potassium permanganate solution added for the blank test
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2 After plugging, place it in a dark place for 40 minutes
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This time can also be adjusted according to the characteristics of the sample
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3 Add excess potassium iodide solution: titrate with sodium thiosulfate standard titration solution.
When the solution is light yellow, add 0.
5 mL starch indicator solution, continue titrating until the blue color disappears, and record the consumption of sodium thiosulfate standard titration solution Volume
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4 During the measurement, follow the same steps as the measurement, replace the sample with the same volume of water, and use the same amount of reagent solution to do a blank test
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5 Result calculation

Potassium permanganate index p, the value is expressed in mg/100mL, calculated according to formula (1):

Where:

V ₀ ―The value of the volumetric volume of the standard sodium thiosulfate titration solution (3.
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4) consumed in the blank test, in milliliters (mL);

V— The value of the volume of the standard titration solution (3.
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4) of sodium thiosulfate consumed by the sample , in milliliters (mL);

c — The exact value of the concentration of sodium thiosulfate standard titration solution, the unit is moles per liter (mol/L);

M— The value of the molar mass of potassium permanganate (1/5KMnO ₄ ), in grams per mole (g/mol) (M=31.
61);

V ₂ —The value of the sample volume: the unit is milliliters (mL)
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Take the arithmetic average of the two parallel determination results as the report result
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The allowable difference between the two parallel determination results is specified by the product standard
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Related links: Determination of reduced potassium permanganate substances (1)