Homework Help: lab equipment (chem)

Posted by ~christina~ on Sunday, December 2, 2007 at 11:25pm.

Why is it that in particular experiments they say to use a Hirsch funnel while we have both the Hirch funnel and the buchner funnel at our disposal. In my opinion I prefer to use the buchner funnel to using the Hirch funnel because product gets stuck in the funnel and scraping the product out does not get all of it out.

The buchner funnel however is great for getting all the product out by just sliding it off the filter paper.

So is there a reason why in some cases you would use the hirsch funnel as opposed to the buchner funnel?

lab equipment (chem) - DrBob222, Monday, December 3, 2007 at 12:22am
I have, at times, lost solid in the
Buchner funnel because the paper was a) a little too small, b)the edges of the paper didn't seal, or c)the vacuum pulled some of the solid through the paper. I didn't have a Hirsch funnel at my disposal; therefore, I never used one.
lab equipment (chem) - ~christina~, Monday, December 3, 2007 at 8:48am
The Hirch funnel in practice should be washed I assume just like the fritted filter funnel with acid and base but we don't wash ours.(very bad as when I use alconox it gets stuck at the bottom of the funnel and it seems some product has gotten lodged in the porous surface as well.)

I don't feel the buchner funnel is any worse in some situation like when you have crystals which are composed of water and other compounds. I learned this since I used the hirsch funnel and it didn't do a good job and a whole lot of the product was lost as I saw it in the flask and below the hirsch funnel filtering disk.

I asked whether we were supposed to weigh the hirsch funnel before filtering as I knew that there was going to be product stuck in there as it was inevitable and I was told, no. This in my opinion is totally brainless as I was just told to scrape out as much as I could. This would be fine but then we are told to calculate the percent yield and I don't see how they can tell people to do this with about 1/3 of the product still in the funnel.

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