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INTRODUCTION TO THE LAB: THE STANDARDISATION OF POTASSIUM PERMANGANATE
WHAT IS STANDARDISATION?
A solution of known molarity is called a standard solution. Its concentration is determined by a process known as standardization. If you have a primary standard (a compound which is very pure, stable, nonhygroscopic, and with a high molecular weight) you can prepare a standard solution simply by dissolving a known amount of the compound in a known volume of liquid.
If you don't have such a compound, you'll have to standardize your solution against a primary standard. For example, you can standardize a silver nitrate solution by using it to titrate NaCl, which is a primary standard. The concentration of the silver nitrate solution can be found from measuring the volume of NaCl needed to react with AgNO3.
IN TERMS OF KMNO4
If a solution of potassium permanganate is prepared directly from crystals it is found that the solution is unstable an that the molarity changes over time (it is therefore not a primary standard). A standard solution cannot therefore be prepared by just weighing out the required mass of crystals and dissoliving them in water. In order to determine the concentration of KMnO4, it must be standardized against a primary standard. Oxalic acid is often used as this primary standard.
Instead a solution of approximately the desired concentration may be made up and stabilized by boiling, allowing the solution to stand for 24 hours and filtering. The stabilized permanganate solution may then be standardized. A solution prepared in this way can be kept for several weeks without marked change in its concentration.