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Topic: Why we need to fold up a filter paper for simple filtration?  (Read 17317 times)

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Offline Winga

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Why we need to fold up a filter paper for simple filtration?
« on: September 20, 2005, 10:52:57 AM »
What is the explanation?
« Last Edit: September 20, 2005, 01:10:17 PM by Winga »

Offline Dude

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Re:Why we need to fold up a filter paper for simple filtration?
« Reply #1 on: September 20, 2005, 04:31:49 PM »
You don't need to.  Filter paper is only folded if you need to fit a flat two dimensional piece of filter paper into a 3-D conical funnel.

Offline Winga

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Re:Why we need to fold up a filter paper for simple filtration?
« Reply #2 on: September 20, 2005, 06:52:50 PM »
You don't need to.  Filter paper is only folded if you need to fit a flat two dimensional piece of filter paper into a 3-D conical funnel.
Mmm...I mean the case you mentioned. ;D

What is/are the advantage(s)?

Offline mike

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Re:Why we need to fold up a filter paper for simple filtration?
« Reply #3 on: September 20, 2005, 08:12:54 PM »
Increases the amount of surface area available for filtration.
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Offline lemonoman

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Re:Why we need to fold up a filter paper for simple filtration?
« Reply #4 on: September 20, 2005, 10:35:42 PM »
If you dont fold it, then it'll kinda bunch up in certain places.

Folding helps the filter paper to actually take the shape of the cone EXACTLY because sometimes when you're filtering, you need a PERFECT seal...not having a seal can cost up to hours (and I'd imagine maybe even days in special cases)

Offline Winga

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Re:Why we need to fold up a filter paper for simple filtration?
« Reply #5 on: September 21, 2005, 04:42:38 AM »
Increases the amount of surface area available for filtration.
So, could you tell me that what's the surface area difference between 8-folded and 16-folded filter papers? (or even an unfolded one)

Offline mike

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Re:Why we need to fold up a filter paper for simple filtration?
« Reply #6 on: September 21, 2005, 04:46:14 AM »
Of course I can. There is no difference in surface area.

However, there is definetly a larger surface area than if you were to simply fold the paper twice and place it flat against the sides of the funnel, do you agree?
« Last Edit: September 21, 2005, 04:46:48 AM by mike »
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Offline Winga

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Re:Why we need to fold up a filter paper for simple filtration?
« Reply #7 on: September 21, 2005, 05:36:25 AM »
Of course I can. There is no difference in surface area.

However, there is definetly a larger surface area than if you were to simply fold the paper twice and place it flat against the sides of the funnel, do you agree?
As I learned that in secondary school and demonstrators in my university, one of the advantage of increasing the folds of a filter paper will give a higher efficiency of diffusion by increasing the surface area.

I wonder know how can it increase the surface area?
Their surface areas should be the same I think.

Assuming "R" is the radius of the filter paper, no matter the no. of folds it is, the length of the folded paper is also "R".
OK, if there are 2 filter papers (+ 1 funnel each), one is 8-folded, another is 16-folded, when the mixture is poured into them as same level, for example 1/2R, their areas are the same (assume there is no overlapping between each folding section), am I right?

One thing I want to point out is that, as the folds of filter paper increase, the volume of the cone (just imagine it looks like a cone) decrease, do you agree?
You can see that the cone is smaller and the angle of it is also smaller than less folded one.

For same area but difference in volume, therefore, the surface area to volume ratio increases as no. of folds of filter paper increases, just like the case of diffusion of red blood cell that why it is biconcave in shape. This give a higher efficency of diffusion (filtration).
Do you agree?

Offline mike

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Re:Why we need to fold up a filter paper for simple filtration?
« Reply #8 on: September 21, 2005, 05:49:01 AM »
Cool, sounds right to me.

I think generally people compare the fluted to the simple cone when refering to the surface area difference though. Check out the pics at this site.

http://www.chem.ubc.ca/courseware/235/danalabsess/flutedfilterpaper.html
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Online Borek

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Re:Why we need to fold up a filter paper for simple filtration?
« Reply #9 on: September 21, 2005, 06:04:59 AM »
I wonder know how can it increase the surface area?
Their surface areas should be the same I think.

If you put filter into the funnel without 'fluting' the surface will be that of a funnel cone. If you 'flute' the filter it no longer touches funnel with it whole surface, and the surface used for filtration is that of the whole filter - thus larger. No matter how many folds are there, the surface will not change of course. That's the same situation as with the air filter in the car, it is often made of folded paper.

What is not clear to me is if the larger surface will be more effective when it comes to speed of filtration, as with folded filter you are loosing sucking from the funnel leg. Probably it all depends on the type of precipitate you are trying to separate.
« Last Edit: September 21, 2005, 06:16:37 AM by Borek »
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Offline Winga

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Re:Why we need to fold up a filter paper for simple filtration?
« Reply #10 on: September 21, 2005, 10:02:13 PM »
I think I mixed up filtration with diffusion.
However, the mixture should filtrate faster with increasing folds.

Offline mike

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Re:Why we need to fold up a filter paper for simple filtration?
« Reply #11 on: September 21, 2005, 11:17:11 PM »
I am really interested now as to what prompted the question. What were you trying to filter? :)
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Offline Winga

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Re:Why we need to fold up a filter paper for simple filtration?
« Reply #12 on: September 22, 2005, 05:51:36 AM »
I am really interested now as to what prompted the question. What were you trying to filter? :)
Just for curiosity! (I saw my demonstrator folding a filter paper)

A compound containing R-Si-O.

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