Sciencemadness Discussion Board

Drying agent- which one to choose?

Mixe - 14-12-2021 at 05:20

It's a big question I know, and no, I don't have a specific process in mind. As a bit of a n00b, I'm looking for tips and tricks, mnemonics, do's and donts and rule-of-the thumbs.

I understand to avoid acidic desiccants in basic solutions and vice versa, but when is sulphuric acid a good choice and when is it catastrophic?

My list of available drying agents so far:

Magnesium Sulphate
Calcium Chloride
Calcium Sulphate
Sodium Chloride
Sodium Sulphate
Sulphuric Acid

And I have a bunch of old 3A Molecular Sieves lying around in desperate need of Time In Oven.

So any tips and tricks are appreciated when it comes to the fine art of drying stuff. Either as common chemistry 1.01 or from personal experience.
ELI5 is always good, I have a huge tolerance for being talked down to.

karlos³ - 14-12-2021 at 06:38

If you don't have a specific use in mind, look at some compability charts regarding drying agents and solvents.
Because it depends on the situation, as usual.

Mixe - 14-12-2021 at 09:54



[Edited on 2021-12-14 by Mixe]

DraconicAcid - 14-12-2021 at 12:14

Calcium chloride is good for non-polar organic stuff, but can really mess up alcohols or carboxylic acids. (We use it in the lab to dry esters, but we have to use the pellets- if someone accidentally uses the dust, they get a gel.)

Mixe - 14-12-2021 at 13:02

Ok, thanks! That's just the kind of advice I'm gunning for. I have flakes, hopefully they work as well.

Texium - 14-12-2021 at 13:02

Magnesium sulfate is my go to for almost everything. It’s easy to prepare, it’s easy to store, and it isn’t deliquescent. What more could you ask for?

Triflic Acid - 15-12-2021 at 07:50

For regenerating your molecular sieves, try microwaving them for 5 minutes. Much faster than oven-dry, but be careful that you don't leave them in too long, otherwise they'll melt. Apparently molecular sieves above microwaves really well.

yobbo II - 15-12-2021 at 12:09

See the book:

You can get it here

It list drying agents etc


macckone - 16-12-2021 at 07:10

sodium chloride is not a good drying agent.

potassium carbonate is a fair drying agent for ethanol.
the list posted is completely missing basic drying agents such as sodium hydroxide, sodium metal, and activated magnesium (made by adding a touch of iodine).
activated aluminum is also a good drying agent (either mercury amalgam or similar, can be used in combination with sodium hydroxide).

Tsjerk - 16-12-2021 at 12:26

Magnesium is also easily activated by stirring for a minute or so in 1% HCl.