[Laskas]

Hey guys,

I'm trying to synthesize Magnesium Benzoate from Sodium Benzoate and Magnesium Chloride. I've used 1.44g of Sodium Benzoate giving 10.0 mmol and 1.02g of Magnesium Chloride Hexahydrate giving 5.0 mmol. I'm attempting to synthesize it using the protocol from a recent paper which states: "...group 2 metal salts of benzoate were obtained by reaction of a nearly saturated aqueous solution of the Na salt with a slight excess of an aqueous solution of MCl2. After stirring for apprximately 1 h, the colorless precipitate was collected by filtration and then recrystallized from water." I've tried it twice this way, one with 5.0 mmol of Sodium Benzoate and 5.5 mmol of Magnesium Chloride Hexahydrate, and the other as described above. In both cases I get absolutely no "colorless precipitate" from the reaction and I've also tried cooling it down. Any ideas what's going on?

[Honclbrif]

What's the K_sp of magnesium benzoate? Have you tried running it more concentrated?

[Honclbrif]

Furthermore, supersaturation happens. Try chilling it down in a glass container, and scratching the interior with a glass rod. Nucleation sites kick start crystal growth and its pretty cool to watch too.

[bessieboy521]

Sometimes you can boil the solution down until a precipitate forms, then drop wise add Hot solvent (water in this case) until your precipitate disappears.  then let it sit to slowly cool. When its at room temperature, if no crystallization has started, you can ice bath it / scratch the glass inside the beaker, like Honclbrif said. If standard Ice water isn't cold enough, you can use Ice and Acetone, which will get you a bit colder. Usually though, if you reduce your solution to the point of precipitation and then barely redissolve, you will most certain get a precipitate. For supersaturated solutions, you can try introducing a small crystal of either your product or even your starting material. YouTube "hot ice" that's a fun demonstration of a supersaturated solution of sodium acetate being crystallized. Best of Luck!