製備高錳酸鉀標準溶液的步驟

to prepare this standard solution you need to dissolve an approximately amount of the solid and made up solution. As someone mentioned here the KMnO4 may contain some solid which is MnO2 --- this can make error in titration!! To eliminate this effect, somone suggest stand the solution overnight to let the solid settle down to the bottom and decant the upper part of KMnO4 solution before use, or someone suggest use glass wool(do not use filter paper!!) to filter off the solid impurity.
After that you can use ammonium iron(II) sulphate or oxalic acid to standardize the KMnO4.... if you prepared plenty of KMnO4 solution, you need to“update” the concentration of KmnO4 after a period of time........

The solid of KMnO4 cannot be stored pure for ong time, that means a standard solution of KMnO4 cannot be prepared by weighting a sample and dissolved it to a certain volume say 250 cm3. as the KMnO4 solid will contain impurity. A standard KMnO4 solution is prepared by making solution of rough concentration, [ by weighting a certain mass of KMnO4 and dissolve in a certain small amount of water and then make up to say 250 cm3. the accurate concentration is obtained by titration with a standard Fe2+ solution. Therefore, the KMnO4 solution can only be a secondary standard solution. It cannot be a primary standard solution.

M1V1=M2V2..........mol/v =M.....V X M =no. of mol
M=mol/dm
1dm=1000cm3
當佢100cm3
let 4mol 咁佢的的濃度= 4/0.1=40M
當40M的時候用上面的公式
40X 0.1=0.04X V2
V2=100dm3
100--0.1 =(99.9dm3)--------要加入水的體積