Why we heat KMnO4 and filter when prepare it

I assume you prepared it by heating, then filtering with a porous filter (not paper). this is because manganese dioxide can precipitate, and you have to filter it out.

Bob Pursley is correct. KMnO4 decomposes to MnO2 when heated and one must filter, preferable through a "fine" or "ultrafine" Selas filter to remove the MnO2. Also, it is worth noting that KMnO4 solution should be standardized and used immediately because precipitation of MnO2 occurs upon standing only a short time.

When preparing KMnO4, there are several steps involved, and heating and filtering are often included in the process. Here's an explanation of why these steps are necessary:

1. Heating: Heating the KMnO4 solution serves a few purposes:
- Accelerates the reaction: Heating the solution increases the rate of reaction between the reactants, which helps in obtaining the desired product in a timely manner.
- Increases solubility: KMnO4 is more soluble in hot water compared to cold water. Therefore, heating the solution helps in dissolving KMnO4 more effectively and obtaining a higher concentration of the compound.
- Evaporates excess water: By heating the solution, excess water can be evaporated, allowing for the concentration of KMnO4 to increase.

2. Filtering: After the heating process, filtration is done to separate any insoluble impurities or solid particles present in the KMnO4 solution. This ensures a cleaner and purer solution.

To carry out the heating and filtration process for preparing KMnO4, here's a step-by-step guide:

1. Measure a specific quantity of KMnO4 crystals and add them to a suitable container.
2. Add distilled water to the container with KMnO4 crystals, ensuring that the crystals are completely immersed in water.
3. Heat the mixture with gentle stirring to aid dissolution. Heating should be done until all the crystals dissolve, but avoid boiling.
4. Once the KMnO4 is fully dissolved, allow the solution to cool down to room temperature.
5. Set up a filtration apparatus, which typically includes a funnel and filter paper.
6. Slowly pour the cooled KMnO4 solution into the funnel, allowing it to pass through the filter paper. This will separate any solid impurities present in the solution.
7. Collect the filtered solution in a clean container, ready for further use or storage.

By following these steps, you can obtain a purified KMnO4 solution by heating and filtering it accordingly.