MgSO4 filtration problems...

mk-1 · Thu Mar 31, 2005 12:17 am

hello bees Smile

REcently ive tried to dry methanol (commercial anhydrous) with MgSO4.
Ive dropped in the xtals, shake it about, and then filter thru a buchner. I then proceeded to filter again.
Upon checking evaporation of the filtered methanol, it left a white residue.
methanol out of the bottle did not leave any residue.
Can anyone explain whats going on? Its a bit wierd, since I assumed it owuld filter all away...

Embarassed

nubee · Master Archiver

if something is disolved in a liquid it can generally get through most attempts at filtering, what your residue is im not sure.

mk-1 · Thu Mar 31, 2005 7:32 am

was wondering if anyone encountered this as well? maybe MgSO4 isnt goot for MeOH...

Darkblade48 · Thu Mar 31, 2005 8:18 am

I would have thought that the MgSO4 would dissolve slightly in the methanol

ApprenticeCook · DILLIGAF

If you bought supermarket epsom salts as your source of MgSO4 then you would have impurities all over the place... the residue could well be a small amount of MgSO4 soluble in the methanol, but if its store bought stuff its more likely an impurity which was initially soluble in the methanol.

-AC

mk-1 · Fri Apr 01, 2005 3:40 pm

my chems are always CP (chemically pure) grade or higher. This MgSO4 was of analytical grade (stated on the bottle 99.9%, from a commercial chem supplier).
So it does dissolve a bit in methanol... Good to know...

Thanks!

IndoleAmine · Dreamreader Deluxe

Try and distill your "dried" MeOH, you should easily get rid of the solubles this way.

Then use silica gel for drying Wink

.

i_a

mk-1 · Sun Apr 03, 2005 1:35 am

ill give the silica gel a go Smile

YeY I_A!!

Maya · Mon Apr 04, 2005 6:05 pm

It was analytical grade MgSO4 but did you remember to take out the heptahydrate first from the MgSO4? it will dissovle a little if you don't first take it out

jsumner · Mon Apr 04, 2005 6:26 pm

Just another thought but I have found that if you do not ensure that the filter paper is already well sealed (?) on the buchner that you will initially get some powder slipping around the filter paper. This is a possibility IMO. Wet the filter paper and get the vacuum going first. Just a thought.

JS

mk-1 · Tue Apr 05, 2005 3:44 pm

heptahydrate was not removed, but the filter paper was wetted first, and no powder was transfered this way.
could be that the heptahydrate caused the problems, next time ill dry the MgSO4 in the oven at 300degC

Maya · Wed Apr 06, 2005 4:39 pm

THAT IS YOUR PROBLEM!

Once you remove last traces by drying it will not happen again