Sciencemadness Discussion Board

Isolating a deliquescent crystals from a saturated solution

barbs09 - 17-9-2021 at 01:20

Hi, I was hoping someone can either point me to a good review or supply a few pointers on obtaining crystals from a deliquescent salt solution. I have searched the "F£$king search engine" with mixed results. I have a solution of Lithium Bromide which I have in a wide mouthed porcelain evaporating bowl over a heater. It has reduced significantly in volume and on cooling does crystallise to a greasy wet mass. At this stage, if I transferred it to a closed container with a good surface area of say anhydrous Magnesium sulphate or copper sulphate, could I potentially get it to the stage of being a bottleable reagent? many thanks, AB

Bedlasky - 17-9-2021 at 11:12

I think yes, I have once solution of very very soluble salt, which refused to crystallize, so I must put the beaker to the plastic bag with CaCl2 to obtain crystals.

You can try to dry your LiBr in owen. This should also work.

Oxy - 17-9-2021 at 11:52

You can easily remove the water by applying heat and vacuum. RBF with gas take-off adapter connected to vacuum pump or water aspirator and placed in heating mantle will be more than enough.
I used that for drying CuBr2 from wet, watery mass to crystals.

macckone - 24-9-2021 at 07:58

recrystalizing from isopropanol is going to work better.
n-propanol works best but is not as easily available.
take your hot saturated solution of LiBr in a liquid state and dump in isopropanol.
you should get an immediate precipitate of LiBr crashing out.
you can then take your solution and repeat the process of boiling it down to concentrated (possibly reclaiming the isopropanol) and repeat.

isopropanol has a 2:1 solubility coefficient between boiling and 0C.
Recrystallizing from dry isopropanol should yield nice crystals.

If you just want dry crystals (anhydrous), you are going to have to use a vacuum dessicator of some kind with heat.
Oxy's suggestion of a rbf with vacuum take off is a good one.

Solubility of LiBr in alcohols:

WGTR - 24-9-2021 at 10:53

One ancillary tip is to crystalize the salt on some Teflon film (or plastic bag) fitted inside of a crystalizing dish. That way you don't have to scrape the dry salt off the glass.

It seems that wet LiCl decomposes a bit under heating. Isn't it normally dried under flowing dry HCl? I suppose LiBr is more resistant to this type of decomposition.

barbs09 - 24-9-2021 at 20:28

Thanks, heaps to work with here.