How to prepare a standard potassium permanganate solution

Weigh 3.3 grams of potassium permanganate, dissolve it in 1050 milliliters of water, bring to a slow boil for 15 minutes, allow it to stand in the dark for two weeks, filter it using a treated glass crucible of type 4, and store it in a brown bottle. The treatment of the glass crucible involves boiling it in a crucible of the same concentration for 5 minutes

You can download the guide on the preparation of chemical reagents and standard solutions from the resources section; it provides detailed explanations. As an analyst, this is one of the most essential reference materials to have on hand, so it’s recommended to download it and save it. This post was last edited by limingshuguang on 2009-2-10 at 09:50.]

Agreed, :handshake

IV. Preparation and Calibration of KMnO4 Standard Solution 1. Preparation: Weigh a slightly larger amount of KMnO4 than is required for the calculations, dissolve it in a certain volume of distilled water. Heat the solution to boiling point, maintain it at a gentle heat for 15 minutes, and then let it stand for two weeks to ensure that all reducing substances are completely oxidized. Filter the solution using a microporous glass funnel to remove the MnO2 precipitate. Transfer the filtrate to a brown bottle for storage, in order to prevent KMnO4 from decomposing when exposed to light. Taking a standard concentration of 0.1 mol/L as an example, 3.3 g of KMnO4 is weighed and dissolved in 1050 ml of water. The mixture is then allowed to boil slowly for 15 minutes; after cooling, it is stored in the dark for two weeks. Filtering is carried out using a P16 glass filter funnel (previously boiled in KMnO4 solution of the same concentration for 5 minutes), and the filtrate is transferred into a brown bottle (rinsed 2–3 times with KMnO4 solution). 2. Calibration: The calibration reaction is as follows: 2MnO4- + 5C2O42- + 16H+ → 2Mn2+ + 10CO2 + 8H2O. 0.2 g of anhydrous sodium oxalate (Na2C2O4), which has been dried at 105–110°C until a constant weight is reached, is weighed to an accuracy of 0.0001 g and dissolved in 100 ml of (8+92)% sulfuric acid solution. It is then titrated using the prepared KMnO4 solution. When the endpoint is reached, the temperature is raised to 65°C, and titration continues until the solution remains pink for 30 seconds; this is used as a blank test. Note: At the start of titration, the reaction rate is slow, so the titration speed must be low. Once the reaction begins, the catalytic effect of Mn2+ increases the reaction rate, allowing the titration speed to be increased. Heating to 65°C near the endpoint is done to ensure complete reaction between KMnO4 and Na2C2O4. 3. Calculate 1000m C(1/5 KMnO4) = ------------------------- (V – V0) × M(1/2 Na2C2O4). M(1/2 Na2C2O4): the molar mass based on the basic unit of (1/2 Na2C2O4) is 67.00 g/mol

1. Preparation of the potassium permanganate standard solution: Weigh 1.0 g of solid KMnO4 on a balance, place it in a large beaker, and add water until the volume reaches 300 mL (a little more water can be added since the water will evaporate during boiling). Boil for about 1 hour, then allow it to cool. After that, filter it using a microporous glass funnel or a glass wool funnel. The filtrate is poured into a brown flask with a narrow mouth, labeled, and calibrated after one week. Save for backup. 2. Calibration of the potassium permanganate standard solution: The KMnO4 solution is calibrated using Na2C2O4 solution. Three portions of 0.13–0.16 g of the reference substance Na2C2O4 are accurately weighed and placed in 250 mL conical flasks. Approximately 30 mL of water and 10 mL of 3 mol•L-1 H2SO4 are added to each flask; a watch glass is then placed on top, and the mixture is slowly heated to 70–80°C (the temperature at which vapor begins to appear). While still hot, the solution is titrated with potassium permanganate solution. At the beginning of the titration, the reaction rate is slow; once Mn2+ is present in the solution, the titration rate can be increased appropriately, until the solution turns slightly red and remains that color for half a minute – at which point the endpoint is reached. Calculate the concentration of KMnO4 based on the mass of Na2C2O4 and the volume of KMnO4 solution consumed. Treat the other two samples of Na2C2O4 solution in the same way; the relative average deviation should be within 0.2%. Precautions: 1. Distilled water often contains small amounts of reducing substances, which cause KMnO4 to be reduced to MnO2•nH2O. The fine powdery MnO2•nH2O contained in commercially available potassium permanganate can accelerate the decomposition of KMnO4; therefore, the KMnO4 solution is usually boiled for a while, and after cooling, it is left to stand for 2–3 days to allow full reaction to occur, after which the precipitate is filtered out. 2. At room temperature, the reaction rate between KMnO4 and C2O4- is slow; therefore, heating increases the reaction rate. However, the temperature cannot be too high; if it exceeds 85°C, part of H2C2O4 will decompose, according to the following reaction: H2C2O4 → CO2↑ + CO↑ + H2O. 3. The acidity of the sodium oxalate solution is approximately 1 mol•L-1 at the start of titration, and around 0.5 mol•L-1 at the end of titration. This helps to ensure that the reaction proceeds properly and prevents the formation of MnO2. If a brown turbidity (MnO2) appears during the titration process, H2SO4 should be added immediately to remedy the situation and eliminate the brown turbidity. 4. At the start of titration, the reaction is slow; a second drop should not be added until the first drop of KMnO4 has completely faded. Once the reaction produces Mn2+, which accelerates the process, the titration rate can be increased appropriately; however, if it is increased too much, the local concentration of KMnO4 becomes too high, leading to its decomposition, the release of O2, or the oxidation of impurities, all of which can cause errors. If the titration rate is too fast, some of the KMnO4 will not have time to react with Na2C2O4 and will instead decompose according to the following equation: 4MnO4- + 4H+ ==== 4MnO2 + 3O2↑ + 2H2O. The endpoint for titrating with KMnO4 standard solution is somewhat unstable; when the solution turns slightly red and this color does not fade within 30 seconds, the titration can be considered complete. If there are doubts about the endpoint, one can first record the reading on the burette, then add one more drop of KMnO4 standard solution. The appearance of a purplish-red color indicates that the endpoint has been reached. It is important not to exceed the equivalence point during titration. 6. The KMnO4 standard solution should be kept in an acid burette. Since the KMnO4 solution is very dark, it is difficult to see the curve of the liquid surface; therefore, readings should be taken from the highest point of the liquid surface.