2 replies to this topic

[sasman]

I am looking for help on simple chemical purifications?..specifically on the tools i will need to do the job properley...and also the correct procedures involved..

I have bought a large plastic funnel and some 12" diameter whatmans filter paper.. but in use this is very very slow..infact it takes over 1 hour per gallon to filter..

I know the basic principles of recystalisation...But take this example..

I add solution A to soultion B and get a precipiate C i filter using filter/paper/funnel..

1 . How do i rinse the precipitate?

2. How do i get the precipitate on? to the filter paper then off the filter paper??

3. how many times typically would i have to recrystalize to get good purity?

4 is there a better way to filter instead of using filter paper? (vacum filtration)

Any tips & advice on basic laboratory procedure..or any webpages? .I have seen on Ebay a buchner funnel? what does this do? and will it be usefull ?

I have a few gallons of chemicals to play with and if i do it in small amounts i will lose a lot of chemicals... wasted materials etc...so want to perfect my technique..

Cheers

Edited by sasman, 28 May 2005 - 01:03 PM.

[Arthur Brown]

Filtration, choose your media carefully Whatman do many grades of media, fast and sluw, coarse and fine, also they do (did) GF-A and GF-B Glass filter circles for aggresive mixtures. Normally filtration is by gravity the filtrate falls through the media. The conical fold of paper - two folds a right angles means that one quarter of the media filters singly and three quarters lying together filter triply. learn the star fold method then all the media is used. Buchner funnels are used for vacuum filtration, you need a vacuum vessel sealed (removably) below the funnel big enough to hold all the liquor with plenty of headroom. The funnel has a flat perforated plate that the media sits on, you pour the mix in onto a damped filter paper with the vacuum holding the media in place the crystals should sit in a heap on the media. Controlling the conditions will control the size of crystal formed,small crystals BAD they clog the media, big srystals GOOD they sit ON the media ready for recovery with a spatula (spoon scoop etc)

Oh you need a vacuum pump thats resistant to the liquid as well maybe one run from the water tap.

Edited by Arthur Brown, 28 May 2005 - 02:51 PM.

[sasman]

I have just being browsing thru some of my Best of AFN books and just read an article written by i think Tom Perigrin..

He mentions that if you started off with a potassium perchlorate solution contaminated with a 10% sodium sulphate .. when you recrystalize the ClO4 you get a product that is over 99.** pure can't remember the exact % .. but that has surley got to be pretty good?..He mentions that you have to recrystalize the solution very slow to get a pure product..

So if i were to recrystalize twice that means the final product must be as good as anything you can buy?