Why use glass wool instead of filter paper when filtering potassium permanganate?

Question

I was preparing potassium permanganate at school. This was to be used for a redox titration later.

We weighed out 1.58g, dissolved it in 500mL of water. The instructions tell us to boil the solution for 10 minutes so that any oxidisable contaminants could oxidise and not stuff up the numbers later.

After that, we were meant to transfer the solution into a storage bottle. We did this by stuffing a bit of glass wool into a funnel and filtering it through into the bottle.

Now, I understand that the filtering was to remove any of said contaminants, right, but now the teacher's gone ahead and asked us why we used glass wool and not normal filter paper.

Is it because the hot solution would break up the filter paper and reduce its effectiveness? Does it have anything to do with heat (I read that glass wool is commonly used as an insulator)? Does it have to do with the material difference between glass and paper? The effectiveness of the filtering? Does it have something to do with redox? Clues would be good, but straight out answers would be brilliant.

Answer 1

The boiling is to ensure all permanganate dissolves; any reducing contaminants will react with the permanganate rapidly. The product of this oxidation is manganese dioxide, which is also a common contaminant. The need to filter arises from Manganese Dioxide (which is insoluble in both boiling and cold solution). This MnO2 catalytically destroys the permanganate with time, so its essential to remove it; otherwise the concentration of manganate will continually drop.



Filtering it with glass wool is common for many chemicals, which are typically corrosive. Manganate when hot _may_ react with filter paper, whereas glass wool is pretty much inert. An example of when glass wool is essential is the filtration of certain ionic liquids which dissolve filter paper!

Answer 2

Glass Wool Filter

Answer 3

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RE:

Why use glass wool instead of filter paper when filtering potassium permanganate?

I was preparing potassium permanganate at school. This was to be used for a redox titration later.



We weighed out 1.58g, dissolved it in 500mL of water. The instructions tell us to boil the solution for 10 minutes so that any oxidisable contaminants could oxidise and not stuff up the numbers...

Answer 4

Organic compounds, including the cellulose of filter paper, will reduce Mn from +7 in the permanganate ion to +4 in the MnO2. That is what we are trying to avoid. Therefore, no more organics should come into contact with the KMnO4 solution after it has been boiled.



The glass wool is used because it contains no organic compounds.



In addition...



When filtered through paper, there would be some residual KMnO4 left in the paper. When the paper dries there will be solid KMnO4 in contact with a combustible material, paper. Since KMnO4 is a good oxidizer, this is not a good combination.



The glass wool is used because it is non-combustible.



========== Follow up ============



Note: Filpi mentioned oxidation to get MnO2. The conversion of MnO4^- to MnO2 is not oxidation, it is reduction.

Answer 5

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His64: Glass wool (SiO2) is totally inert to attack by [MnO4]-. On the other hand, filter paper is comprised of organic material that will be oxidized by the [MnO4]- rouning your filter paper and the purity of your KMnO4. Dab a spot of MnO4]- on a filter paper and watch it turn brown (MnO2). cheers, drp