Hygroscopic chemical...how to deal with? - (Jul/17/2010 )

Our lab just purchased a chemical in crystallized form. But it is very hygroscopic...The crystal will eventually turn into water when i am weighting it. This causes I am weighting water instead of real crystal and cannot get accurate molar...any idea?

I don't know if this is applicable.

In the only situation where I encountered this problem, I ended up making a stock solution with the entire contents of the bottle I purchased. I then made aliquots of the stock solution and kept it frozen at -80C. When I needed the compounds I thawed out a stock aliquot.

SO I first weighed a 50ml falcon tube. Added the entire bottle of chemical I purchased. Weighed the bottle+compound again and figured out how much water to add.

For hygroscopic chemicals I usually order them fresh, then seal the opening, put in bag with desiccator, in -20 or -80 if you can.

For example, glycerol is quite hygroscopic, if you leave at RT, it will eventually absorb moisture from the environment and goes from 100% to 80%. So in our lab, we usually store newly bought glycerol in air tight container. If leave in scotch bottle, we usually dilute till 80% (water saturated)

For detergent or lipid, we store the powder at -20, sometimes we make 10% solution stock straight from the freshly bought powder and keep at -20.

I guess you can either store at -20 or you can make a solution stock and keep at -20 (if your chemical is stable in solution)

Some chemists use small weighing bottles or boxes with a ground joint. And of course you've to work fast and a desiccator is helpful of course...
Examples: