Sciencemadness Discussion Board - Evaporating a liquid in desiccator bag

Evaporating a liquid in desiccator bag

bob800 - 11-2-2011 at 14:54

I found a really simple procedure for making copper(II) acetate by woelen:

- Add excess 30% acetic acid to the black material and let it stand in an open vessel for many many days until it has become perfectly dry. Everything will smell of vinegar when you do this inside, so it is best to put the vessel outside in a warm and dry place where animals and children cannot access it. When the acetic acid is added, the liquid becomes really dark green and black material seems not to dissolve at once, but while it is standing, slowly all of it is converted to copper(II)acetate. It is important though to have excess acetic acid.

However, it's really cold outside here, so evaporating outside won't do anything. Having watched a NurdRage video on making a desiccator bag(http://www.youtube.com/watch?v=XJFfS_YbbYI&feature=playe...), I thought I could make one and use NaOH to dry out the air and additionally dissolve the pungent acetic acid fumes.

However, at the end NurdRage says, "This desiccator only works on solids, it does not work on liquids and cannot be used for concentrating acids, peroxide or drying alcohols."

Why won't this work for liquids? Is there any other option for evaporating inside, without filling the whole house with vinegar fumes?

Any help would be very appreciated! Thanks!

Magic Muzzlet - 11-2-2011 at 14:57

You can use the bag to dry your copper acetate.

woelen - 11-2-2011 at 15:04

The simplest option is to wait for summer

A somewhat less simple option is to use a plastic tub which can be closed air-tight very well and put the liquid and a fairly large amount of NaOH in it and just allow it to stand for some time in a warm place. You probably, however, will need quite some NaOH. You could evaporate some of the liquid by heating, but then you run the risk of hydrolysing part of the acetate to the oxide and/or hydroxide and you run the risk of getting an impure product which is not nicely crystalline.

Patience is your best friend in this particular case

[Edited on 11-2-11 by woelen]

bob800 - 11-2-2011 at 15:12

Quote: Originally posted by woelen

The simplest option is to wait for summer

Perhaps I'll have to do that.

Thanks for the quick replies. I'll try the NaOH method, but if it ends up requiring tons of it, I'll put it away until summer.

DougTheMapper - 11-2-2011 at 15:29

I've had good experiences with anhydrous magnesium sulfate.

Get epsom salts at the store and spread the crystals on a cookie sheet. Bake them in the oven as high as the temperature will go. The crystals will first swell and then steam as the heptahydrate is dehydrated. It doesn't small as long as the crystals weren't dusty.

Let cool with as little exposure to air as possible. (Leave it in the oven) You will need a hammer or something of that magnitude to release the stuck-on MgSO4 from the cookie sheet.

Place the product in an airtight container. It works wonders as a desiccant.

entropy51 - 11-2-2011 at 16:43

Quote: Originally posted by DougTheMapper

I've had good experiences with anhydrous magnesium sulfate.

Get epsom salts at the store and spread the crystals on a cookie sheet. Bake them in the oven as high as the temperature will go. The crystals will first swell and then steam as the heptahydrate is dehydrated. It doesn't small as long as the crystals weren't dusty.

Let cool with as little exposure to air as possible. (Leave it in the oven) You will need a hammer or something of that magnitude to release the stuck-on MgSO4 from the cookie sheet.

Place the product in an airtight container. It works wonders as a desiccant.

Sigh. If you put the MgSO4 in a warm oven and slowly raise the temperature of the oven, the salt will dehydrate without melting in its water of crystallization. You will end up with a dry powder. No hammer needed.

But MgSO4 is a good dissicant for drying organic liquids, not for filling a dessicator and trying to evaporate liquids.

ldanielrosa - 12-2-2011 at 00:37

I don't know if this helps, but when I want to evaporate liquids I put 'em in a jar and let it fester for a while in a crock-pot with a sand bath.

desiccating with NaOH

annaandherdad - 23-10-2011 at 09:30

Quote: Originally posted by bob800

Quote: Originally posted by woelen

The simplest option is to wait for summer

Perhaps I'll have to do that.

Thanks for the quick replies. I'll try the NaOH method, but if it ends up requiring tons of it, I'll put it away until summer.

I've been desiccating silver nitrate (in solution with some HNO3) using NaOH. The weather here is cool, but it's still working pretty well. I'm using a Rubber Maid plastic container (which unfortunately are rather expensive, but maybe you can find one in a second-hand store). The top seals on pretty well. As for the NaOH, I'm using drain cleaner (not Drano, which has aluminum in it) that I bought in the hardware store. It's pretty cheap. Of course it doesn't have to be high quality, it just has to absorb the water and acid vapors.

I found that increasing the area of the evaporating liquid has a bigger impact on the rate of drying than does increasing the area of NaOH. So I've ended up with maybe 4 petri dishes of liquid evaporating, plus one container of NaOH, in a single Rubber Maid container.

I learned the hard way not to use a metal container for the NaOH. The problem is not the NaOH, it's the acid vapors that attack the metal. I switched to a plastic tub (originally used for margarine) and that works better.

I have taken to opening the container every 2 days and weighing the petri dishes to measure the rate of evaporation. The weather here is cool, but I can get up to 10 grams of liquid evaporated per day with my setup. It still takes patience, but it works.

The NaOH gets runny after a while. I've just poured off the liquid and put the rest back in, supplementing the NaOH when there's not much left. I read on another thread that someone mixed his NaOH with CaO to absorb the water, with good results. I haven't tried that yet.

I'd use CaCl2 if I didn't have the acid vapors to get rid of. I don't know which has the higher affinity for water, NaOH or CaCl2, but I'm considering a final, extra drying step at the end with fresh (and completely dry) NaOH or CaCl2.

It's been interesting, and I'm thinking of just doing some crystallization for fun of different salts, after I'm done with the AgNO3. My daughter likes to see colored crystals.

One more thing. Both the cheap drain cleaner I bought at the hardware store and the lab quality stuff I bought from a chemical supply place, come in small pellets in a plastic container. When I first open the container, the pellets are so dry that they are all charged with static electricity and clinging all over the sides of the container and the lid. When I try to scoop out a spoonful (with a plastic spoon), the static electricity makes the little pellets jump all over the place, onto my hands and onto the table. Very annoying, especially for NaOH.

However, within a minute or two, the NaOH evidently absorbs enough water from the air to make an electrical conductor, and the static electric effects disappear.

I'd prefer it if they just gave me larger lumps of NaOH so I wouldn't have this problem in the first place.

Arthur Dent - 24-10-2011 at 05:09

Well definitely the good ol trick of a large ziploc seal bag in which you put a dollar-store damp-trap filled with CaCl<sub>2</sub> is the most efficient and inexpensive: Damp Trap @ $1.25 and Ziploc bag @ $.25, total cost a buck and a half. I've succesfully dessicated various chloride solutions, and even got some solid FeCl<sub>3</sub> hydrate out of a concentrated solution.

For more serious dessicating, I use the contents of one of those Damp Traps in my Pyrex vacuum Dessicator with some vacuum (as much as my little plastic aspirator can muster). Does the job very well, see this thread:

http://www.sciencemadness.org/talk/viewthread.php?tid=17364#...

Manganese Chloride crystals from what was originally a fairly dilute solution.

Robert

Chemistry Alchemist - 24-10-2011 at 06:12

would it be warmer inside then out side? normally i leave my liquids in the laundry (gets warm in there sometimes compared to out side or around the house) so i place it ontop of one of those dryers which arnt in use... heat rises to teh sealing, my liquids are about 1 m away from the sealing so after about a week or so i can grow very nice large crystals.... really good way to get nice pure crystals instead of boiling it or rushing drying

theflickkk - 24-10-2011 at 08:22

Maybe you could try boiling down the solution, until a thin crust of copper acetate starts to form,
before letting it cool and evaporating it? I've tried it and it worked well in my opinion. This method gives
many tiny crystals instead of a couple of big ones though.