Thursday, January 03, 2008

How to clean your sintered funnel

Lately when I have been cleaning my sintered funnels people have stopped and asked me what I was doing. To my surprise many chemists don't seem to know how to take a nasty, dirty sintered funnel and making it nice, white and shining again in about 15 minutes.
These days I'm doing lots of old school chemistry that involves heating the crap out of the components using for example conc. sulfuric acid as the solvent. Needless to say things are polymerising and decomposing left, right and centre and when you filter it through your nice white sinter it ends up looking nasty (see picture above). The stuff doesn't go anywhere with acetone, water, 2M sodium hydroxide or hydrochloric acid etc. so what should you do? Before I proceed please note that if you attempt any of the following you must:
(1) Wear a closed lab coat, safety glasses and plastic gloves
(2) Conduct the cleaning in a fume hood with the sash down at all times
(3) Ensure that all the glassware is clean and doesn't contain residual organic material such as acetone
Please take the above advice seriously. People have had nasty accidents doing the following because they weren't careful.
There are two common ways to get your sinter clean:
(1) Conc. nitric acid, or
(2) Conc. sulfuric acid and hydrogen peroxide
Nitric acid is the easy solution and more often than not it does the trick. However, occasionally it is necessary to use more vigorous conditions. I have never had a sinter that didn't become white after treatment with conc. sulfuric acid and hydrogen peroxide and this is generally the method that I use because I know it works every time.
(1) Fit the funnel to a B├╝chner flask attached to a vacuum that you can control easily
(2) Add a small amount of conc. sulfuric acid so that it covers the surface of the sinter
(3) Add a dash of hydrogen peroxide and stand back. Things get pretty hot, bubbly and exciting at this point (See picture above).

(4) When the ingredients have been cooking away for a minute or so apply a very gentle vacuum briefly. This should be sufficient to suck the sinter dry (See picture above),
(5) Allow the cocktail to settle down and cool off and clean all the equipment with lots of water taking care not to pour the contents all over yourself. Your sinter will now look like this.
Too easy but please do be careful guys. D!