Permanganate Index Measurement Experiment
Permanganate Index Measurement Experiment
Permanganate value (Permanganate value) is the amount of potassium permanganate consumed in treating water samples in acidic or alkaline media with potassium permanganate as the oxidizing agent, expressed in mg/L of oxygen. Nitrites, ferrous salts, sulfides and other reducing inorganic substances in water and organic substances that can be oxidized under these conditions can consume potassium permanganate. Therefore, permanganate index is often used as a comprehensive indicator of the degree of contamination of surface water bodies by organic and reducing inorganic substances. There are two methods for the determination of permanganate index, acidic method and alkaline method. Acidic method is suitable for water samples with chloride ion content not more than 300mg/L. Alkaline method should be used when the concentration of chloride ion in water samples is higher than 300mg/L. The acidic method is used in this laboratory.
Operation method
acidification
Principle
After the water sample is made acidic by the addition of sulfuric acid, a certain amount of potassium permanganate solution is added and the reaction is heated in a boiling water bath for a certain time. The remaining potassium permanganate is reduced with sodium oxalate solution and added in excess, and then the excess sodium oxalate is dripped back with potassium permanganate, and the value of permanganate index is found by calculation.
Materials and Instruments
Water samples Move I. Reagents Caveat 1. After water samples are collected, sulfuric acid should be added to make the pH ＜2 to inhibit microbial activity. Samples should be analyzed as soon as possible and determined within 48 h. 2. permanganate index is a relative condition indicator, and its determination is related to the acidity of the solution, permanganate concentration, heating temperature and time. Therefore, it is necessary to strictly observe the operational regulations during the determination so that the results are comparable. 3. After the heating in the water bath is completed, the solution should still maintain a light red color; if it becomes lighter or fades away completely, it means that the dosage of potassium permanganate is insufficient. At this time, the dilution of the water sample should be increased and then measured, so that the residual potassium permanganate after heating is 1/2 to 1/3 of the amount of its addition is appropriate. 4. Under acidic condition, the reaction temperature of sodium oxalate and potassium permanganate should be kept at 60～80℃, so the titration operation must be carried out while it is hot, and if the temperature is too low, it should be heated appropriately. For more product details, please visit Aladdin Scientific website.
Potassium permanganate Sulfuric acid Sodium oxalate
Water bath Conical flask Acid buret Timing clock
1. Potassium permanganate reservoir solution (C1/5KMnO4≈0.1 mol/l): weigh 3.2 g of potassium permanganate dissolved in 1.2 L of water, heated to boiling, so that the volume is reduced to 1.0 L, placed in a dark place overnight, filtered through a G-3 glass sand funnel, filtrate is stored in a brown glass bottle. Before use, it was calibrated with 0.100 mol/l sodium oxalate standard storage solution to obtain the actual concentration.
2. Potassium permanganate use solution (1/5 KmnO4 = 0.01 mol/l): take a small amount of the above solution, dilute it with water to about 0.01 mol/l, store it in a brown bottle and calibrate it on the day of use.
3. (1+3) Sulfuric acid: Prepare by adding potassium permanganate solution dropwise while still hot to a slight red color.
4. Sodium oxalate standard stock solution ( C1/2NaC2O4=0.1 mol/l): weigh 0.6705 g of excellent pure sodium oxalate dried at 105-110 ℃ for 1 h and cooled, dissolved in water, transferred to a volumetric flask, and water was fixed to 100 mL.
5. Sodium oxalate standard use solution ( C1/2NaC2O4=0.01 mol/l): dilute the above solution 10 times with water.
II. Experimental steps
1. Dispense 100 mL of a mixed water sample (or less if the permanganate index is above 10 mg/L and dilute to 100 mL with water) into a 250 mL conical flask.
2. Add 5 mL of (1+3) sulfuric acid solution (Reagent 3) and mix well.
3. Add 10.00 mL of potassium permanganate solution (Reagent 2), shake well, and immediately place in a boiling water bath for 30 min (counting from the time the water bath reboils). The surface of the boiling water bath should be higher than the level of the reaction solution.
4. Remove the conical flask, add 10.00 mL of sodium oxalate standard solution (reagent 5) while it is still hot, shake well, and titrate immediately with potassium permanganate solution reagent (2) to a slight red color, and record the amount of potassium permanganate solution consumed V1 .
5. Calibration of potassium permanganate solution: Heat the above titrated solution to 70°C, accurately add 10.00 mL of sodium oxalate standard solution (reagent 5), and then titrate with 0.01 mol/l potassium permanganate solution (reagent 2) to a slight red color.
Record the consumption of potassium permanganate solution and find the correction factor (K) of potassium permanganate solution according to the following formula.K=10.00/VFormula:V - Consumption of potassium permanganate solution, mL;10.00 - Amount of 0.01 mol/l sodium oxalate standard solution, mL.(6) If the water sample is diluted, another 100mL of distilled water should be taken at the same time, with the same water sample of the procedure for the blank experiment.Record the blank titration of potassium permanganate solution consumption V0 .(vii) Calculation of results(1) Water samples without dilutionPermanganate index (O2, mg/L) = [(10 + V1) × K-10] × M × 8 × 1000/100Eq:V1 - Consumption of potassium permanganate solution when titrating the water sample, mL;K - correction factor;M - concentration of sodium oxalate solution, mol/L;8 - 1/2 O2 molar mass, g/moL.(2) Water samples were dilutedPermanganate index ( O2, mg/L) = ｛[(10+ V1)_K~F10]-[(10+ V0)_K~F10]_undefined M * 8 * 1000/ V2In the formula:V0 - Consumption of potassium permanganate solution in the blank experiment, mL;K - correction factor;M - concentration of sodium oxalate solution, mol/L;V2 - amount of water sample dispensed, mL;C - dilution of water samples containing distilled water ratio, such as 10 mL of water samples with 90 mL of distilled water diluted to 100 mL, then C = 0.90.