Predacon35 - 3-9-2018 at 15:40
Hello
What seems to be the preferred size of filter flasks and funnels?
Also if you have more than one size what do you go for first?
The small 25ml and 50 ml seem to be so little that they could tip over.... the big ones seem just overkill. But any advice is appreciated
Sulaiman - 3-9-2018 at 15:45
If you intend to use filter papers,
first check the availability and prices of filter papers,
then choose a Buchner funnel size to suit.
Here in UK I chose 90mm diameter (from China via eBay)
If you are going for a fritted glass filter funnel then I think that the capacity should be similar to your normal glassware size.
e.g. for my 10/19 glasware kit I use 50ml or 25ml for the pot and 25ml, 10ml or 5ml for the receiver,
so a 10ml funnel should be fine.
(I do not have a fritted funnel, I use patience + gravity + pipetting)
For my 24/29 kit the most common is 500ml and 250ml flasks
so I use my 90mm Buchner funnel with a 250ml (or rarely, 1l) filter flask.
(side-arm Erlenmeyer flask)
I ALWAYS clamp the flask when using my 90mm Buchner funnel
it is top-heavy and has a vacuum hose trying to pull it over.
Overall I would rather have a filter funnel that is too small,
that may require a few batches of filtering to get the job done,
than one that is too large and looses too much product.
[Edited on 4-9-2018 by Sulaiman]
JJay - 3-9-2018 at 16:56
I mainly use a 90mm pore plate funnel with an RBF. That's a good size. I have a 1 L glass fritted funnel, but I hardly ever use it. A 1 L fritted
funnel is overkill for most tasks and a pain to clean; I would suggest something much smaller like 60 mL.
Dr.Bob - 3-9-2018 at 17:54
I find 125 ml filter flasks to be ideal for small Buchners, like 55 mm and 70 mm.
The 250 ml filter flasks are ideal for medium Buchners, like 90 and 110 mm,
and 500 ml filter flasks to be ideal for larger Buchners, like 125 -150 mm. Might need a clamp to hold these.
I have a few of these left, and filter paper for some sizes.
Heptylene - 4-9-2018 at 13:52
The one I use is a 100 ml fritted funnel. Its good for filtering say 0.5 to 50 grams of material at once. Sometimes I wish I had a very small fritted
funnel (25 ml) for small scale reactions, and a very large one (500-1000 ml) for large scales. But overall 100 ml is the best size for my needs.
Don't forget that you'll lose some product on the frit or the filter paper, so if your funnel is too big you won't be able to filter small amounts of
materials. And if its too small you'll have to do your large filtrations in batches.
nimgoldman - 5-9-2018 at 07:18
I have three Buchners for these filter paper sizes:
55 mm
90 mm
125 mm
The largest one is 1L funnel I use for filtering plant extracts and I wouldn't use it in other chemistry taks.
I have one 250 ml sintered funnel (glass frit) - it is sometimes more convenient than filter paper.