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Author: Subject: 2 different buchner funnels. please help
Db33
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[*] posted on 6-12-2016 at 10:35
2 different buchner funnels. please help


i have 2 different glass buchner funnels. One of them has about a 1cm think very hard whats called #3 course filter and looks like this.
s-l500.jpg - 29kB

and i have another one that just has a clear bottom with a bunch of holes that i assume i put filter paper on top of. here it is
s-l500.jpg - 51kB

my question is, for the top one with that thick course filter already in it, do i use filter paper on that? and how do i clean it after? Am i suppose to use filter paper for both of them? Any help would be appreciated. are they meant to filter differnet things?
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DDTea
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[*] posted on 6-12-2016 at 11:06


For the fritted funnel (top), cover the frit with celite. This will pre-filter any coarse particles, keeping them from clogging your frit. After filtering your mixture, chase it with solvent to wash anything that may be clinging to the celite. Cleaning frits can get hairy. In the simplest case, it involves washing with solvent and maybe some dilute acid. Some people like to use piranha fluid to clean their frits, but this is really asking for trouble: a clean frit is not worth the risk of injury/death.

If your goal is to collect the solids, I recommend using the bottom buchner funnel + filter paper.




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macckone
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[*] posted on 6-12-2016 at 12:05


There is a thread on cleaning fritted filters.
General rule is don't use frit with metal ions that
form insoluble sulfates. Then clean with pirhana
which will dissolve anything but those ions.
This including your eyes and skin so use proper
protection.
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[*] posted on 6-12-2016 at 13:26


I think i bought what mostly looks like the bottom photo, but with the filter shown in the top photo.

Hasn't arrived yet.

Basically you just need to experiment with them, use some common sense, and see what happens.

The funnel in the bottom photo definitely needs filter papers.

I got a similar (plastic) buchner and cut the required filter paper size from 'normal' 100mm ones with scissors.

Amazingly not everything gives in to vac filtering, which was a surprise.




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DDTea
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[*] posted on 6-12-2016 at 14:45


Quote: Originally posted by macckone  
There is a thread on cleaning fritted filters.
General rule is don't use frit with metal ions that
form insoluble sulfates. Then clean with pirhana
which will dissolve anything but those ions.
This including your eyes and skin so use proper
protection.


Piranha is corrosive, but the bigger problem is that it causes explosions on contact with organics--which results in lots of flying glass from the apparatus that was being cleaned. There was an infamous incident at Cornell stemming from piranha mixture.




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ahill
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[*] posted on 6-12-2016 at 15:37


I actually broke my glass frit buchner last night - (I am still in morning) and I will definitely be getting another one - I think it was my favourite bit of glass.

TIP - the center tube (at least on mine) is very fragile - I connected a hose to wash trapped particles back out (squirting water thru it in reverse), and as a wriggled the hose to remove it, the tube just snapped near the base.
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Db33
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[*] posted on 6-12-2016 at 15:38


damn is there anything else i can use other than piranha to clean it? i dont wanna worry about explosions.
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DDTea
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[*] posted on 6-12-2016 at 16:16


apologies, i forgot to actually mention what to use! after discarding the celite, washing with water, then acetone, then hexanes, and drying in an oven usually works for me. nitric acid if you need to get more aggressive.



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[*] posted on 6-12-2016 at 16:21


One time when I was inexperienced and decided to filter out very fine carbon with my fritted funnel I ended up having to use chromic acid to clean the frit (also something that you definitely don't want to use on a regular basis, but it works when desperate measures are called for).



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Db33
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[*] posted on 6-12-2016 at 18:11


so which one should i use most of the time? the sintered filter or the one that takes filter paper?
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XeonTheMGPony
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[*] posted on 6-12-2016 at 18:15


As others have said if you can not disolve it don't use it on a frit, use it on the cellulose filter
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[*] posted on 6-12-2016 at 21:40


You should use a paper filter for everything that doesn't dissolve paper, especially if you want to keep the solids. Fritted funnels, I believe, are better for when you want to get rid of the solids and keep the liquids, and want to do a really good job filtering any precipitates out of your liquid.
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[*] posted on 7-12-2016 at 06:05


thank you Melgar
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TheNerdyFarmer
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[*] posted on 8-12-2016 at 14:31


Can't you use filter paper on a fritted funnel?
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[*] posted on 8-12-2016 at 14:34


You could, but that kinda means that you should not have been using the fritted one.

Mine arrived today ;)

Surprising how big the 200ml version looks.




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[*] posted on 8-12-2016 at 15:14


I was wondering because I just have a fritted one and not a regular cellulose Buchner funnel.
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XeonTheMGPony
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[*] posted on 9-12-2016 at 02:44


I've don that, some stuff all ways makes it past the sides a bit, but got to make sure the cellulose is finer then the frit or there is no point!

I need to get a disk style funnel here my self as I don't want to subject the more valuable fritted ones to mechanical wear when unnecessary.
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[*] posted on 22-1-2017 at 01:45


Hello, I intend to filter a gold chloride (Au in aqua regia) from insoluble sediments (quartz mainly) using a buchner funnel. My aim of course is to collect the valuable solute rather than the solids. Given the solution will stream past the vacuum side arm I suspect some droplets will end up in the vacuum stream. Does anyone know of a standard way of setting up buchner funnel with the goal of retaining the liquid? The problem I see is that most buchner funnels have short stems.

Thanks in advance.
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[*] posted on 22-1-2017 at 02:38


Well I have never heard of that being a problem. You could always put a trap in.
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[*] posted on 22-1-2017 at 03:25


there is virtually no airflow in the side arm, (if there are no leaks), the volume of gas is equivalent to the volume of solute filtered :)

for dense precipitates I find gravity, patience and decanting is best for precious fluids as some gets lost when filtering.

I do not own a large fritted funnel, just tiny ones,
but (ideally) you know what you are filtering and so can determine the least hazardous way to clean the filter
most things can be cleaned with water, detergent, petrol, .... household stuff.




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[*] posted on 22-1-2017 at 22:44


Thanks guys, good advice. Sulaiman, I should have thought of that :)
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