Sciencemadness Discussion Board

MgSO4

thunderfvck - 16-3-2004 at 22:45

H2SO4 + Mg(OH)2 ---> MgSO4 + 2H2O

Will this work?

I can obtain Mg(OH)2 as milk of magnesia. And H2SO4 is in my basement.

I need a drying salt.

And CaCl2 just did not work for me...

darkflame89 - 17-3-2004 at 00:26

hmmm...is there a need to dry the solution of MgSO4? You can just have to crystallise out of the solution.

You can try CaO as drying agent, or maybe anhydrous CoCl2

Epsom salts

JDP - 17-3-2004 at 00:53

MgSO4 can be found as Epsom salts in like 5 pound quantitys for dirt cheap, so I don't see the reson for wasting good H2SO4. Unless you just in it for the chemistry of it, in that case, yes your method will work.

thunderfvck - 17-3-2004 at 01:47

REALLY. Epsom salt, huh?

Care to elaborate a tad?

...And MgSO4 IS a drying salt...that's why I need it.

[Edited on 17-3-2004 by thunderfvck]

Saerynide - 17-3-2004 at 02:06

I dont think he wants Epsom salt.

Epsom salt is the heptahydrate. It doesn't dry stuff very well ;)

Esplosivo - 17-3-2004 at 02:15

Epsom salts being the heptahydrate can be heated in a stream of dry air, such as in an oven, to remove the water of crystallization. After a while the crystals should turn into a whitish 'powder'. This is the anhydrous state.

Just a tip but if you are going to use MgSO4 in a dessicator I doubt it would work efficiently. CaCl2 would be the best choice, being highly hygroscopic and very easy to produce. Na2SO4 is another choice for a drying agent, though CaCl2 remains the best in my opinion.

The MSDS for MgSO4.7H2O:
http://ptcl.chem.ox.ac.uk/MSDS/MA/magnesium_sulfate_heptahyd...

thunderfvck - 17-3-2004 at 02:55

So epsom salt IS MgSO4? That's good. Very good.

It's not for a dessicator. I wish I had one though!

I want it to purify some ethanol, I mean that's one of the more immediate thigns I'd do with it. However, I understand that drying salts are good friends to have so I'd like to stock up. I recall reading that CaCl2 forms "alcohols of crystallization" or something of that sort. And so purifying ethanol with CaCl2 would be hopeless.

HCl + CaCO3 --> CaCl2 + CO2 + H2O

This has got to be right.

I stole some chalk from school, reacted with HCl and got this disgusting precipitate. It was greenish and very gross. I did not want to collect and store this chemical so I threw it away. Was this supposed to be CaCl2?

Esplosivo - 17-3-2004 at 03:13

If the chalk was coloured it would have influenced the resulting mixture. Actually the easiest way to make a somewhat pure CaCl2 is to mix hydrochloric acid with an excess of marble chips. After the reaction is complete (ie when the effervescence stops) filter the mixture and evaporate the water. Hydrated CaCl2 will result. Continue heating up the solid and anhydrous CaCl2 will form. CaCl2 is a white solid, which is highly hygroscopic. I use it as a dessicant myself, and I can assure you it works well.

The equation you posted is correct.

CaCl2 is high soluble in water, and therefore when formed it will surely NOT precipitate. The greenish ppt was probably some colouring agent. To get the CaCl2 out of you mixture, filter it and evaporate the water from the resulting solution.

Btw, drying of alcohols is usuaally carried out using anhydrous sodium sulphate. This can made by mixing sodium carbonate/hydrogen carbonate/hydroxide with dilute sulphuric acid until neutralization occurs. Then evaporate the water. Na2SO4 crystals will form, which when heated in an oven will form the unhydrous powder.

[Edited on 17-3-2004 by Esplosivo]

Saerynide - 17-3-2004 at 03:24

I wouldnt bother waste precious HCl to get CaCl2. You can get CaCl2 for dirt cheap (like a couple bucks for a small bucket) in dehumidifiers like Damprid.

Organikum - 17-3-2004 at 06:36

Dehydrating of salts for drying purposes is favorably done in a microwave. Spread the salt on the glassplate and nuke it on half power.
For drying alcohols CuSO4 is often used, it has the advantage that you can see if its wet as it turns blue then, anhydrous it is white/greyish.

Dont expect salts working fast in drying, also with strong stirring it will take at least a day until the job is done and often it will be necessary to replace the salt with freshly dried one at least once. Distilling the dried solvent is advised as the salts are ALMOST insoluble in alcohol but not completely.
Drying EtOH is tedious, timeconsuming and a pest as a pest can be. I prefer IPA as I can buy this unhydrous and it is also easier to dry when wettened. Just salt it out.

Tacho - 17-3-2004 at 08:06

I doubt you will dry ethanol above 95%using drying salts. Do a search. You will find that drying ethanol is a pain. I remember that industrialy its done distilating it with benzene, benzene forms an azeotrope with water that is separated.CaO or magnesium followed by distillation also comes to my mind. Anhydrous MgSO4 will not work

Vogel's book (dowload it from Polverone's page) explain how it can be done in the lab.

Organikum - 17-3-2004 at 10:03

You get EtOH to over 99% anhydrous with CuSO4 - time and changing the salt are necessary though. This 99%+ alcohol can be made completely anhydrous with NaOH - also time, weeks are needed here but it works. Also diethylether can be dried with NaOH this way to an extent being more dry than with sodium wire.

No joke.

thunderfvck - 24-3-2004 at 10:47

Why is it preferable to dry the salt in a microwave?

And is it possible to overheat the salt? Will it break down when overexposed to heat, or am I okay when I leave it in the microwave for 6 minutes...?

[Edited on 24-3-2004 by thunderfvck]

Esplosivo - 24-3-2004 at 11:16

Overheat the salt!?!?! Aren't we talking of an ionic salt with a high, actually very high melting point?! It will not decompose in a microwave if that is what you mean.

Are you sure you can dehydrate the compound in a microwave. Why not use a normal oven or heating the compound in a can over a hot flame?!

thunderfvck - 24-3-2004 at 11:36

Oh yeah. It's working beautifully. BEAUTIFULLY.

I had two choices of epsom salt. The stuff I got, used for constipation, and there was the big bags, for baths and stuff I guess. Is there any difference?

Mine came in a nice, professional looking chemical bottle. The other stuff was in a clumsy bag.

Esplosivo - 24-3-2004 at 11:47

I normally get the same stuff used for constipations from a pharmacy. It seems to be of quite a high grade stuff (probably GPR). Nice to know the water of crystallization is removed in a microwave.

Did decrepitation occur?

thunderfvck - 24-3-2004 at 12:05

Not that I noticed. But I wasn't around while it was in the microwave. There was some violent jumping of the crystals though, which was pretty neat. There wasn't any booming cracks or anything though.

The stuff also clumped together which you're probably familiar with in the oven...I guess. It was a PAIN in the ass seperating all of it, thank GOD I have a mortar and pestle though (just came in yesterday). Now I have a fine white powder. My right arm feels pretty beef now as well, thirty minutes of crumbling up that stuff...oh man...

Esplosivo - 24-3-2004 at 12:29

Good. Are you gonna use the unhydrous magnesium sulphate for drying alcohols now. I like the idea, seems pretty cheap and neat. The grinding lol, that will count as a little exercise :P Yeah the 'clumping' is common even when it is heated in an oven.

Polverone - 24-3-2004 at 13:05

The microwave is nice because it dehydrates the salt much faster than other means. 2 hours in an oven or <10 minutes in a microwave, take your pick.

Sodium acetate is almost the perfect example-compound for microwave drying. Take a bit of non-dry sodium acetate, add a little water, and toss it in the microwave. The water boils off nicely until the whole mass suddenly goes anhydrous almost at once, leaving a light dry compound "fluffed up" from the steam bubbles. It is now very easy to grind into a fine powder.

I did discover, though, that this doesn't work for NH4NO3: it melted and billowed white fumes after the water was gone.

Other salts, (MgSO4 for example) can also be less-well-behaved as they pop and spatter during drying. If you have a cheap microwave to dedicate to chemicals, it is the best way to dry a number of salts.

chemoleo - 24-3-2004 at 15:34

Hmm, I always thought CaCl2 can NOT be made anhydrous by evaporating crystal water - I thought it decomposed similar to Aluminium chloride hexahydrate, to CaO/OH and HCl?!?

But then, how is anhydrous CaCl2 made?? surely not by reacting the elements?

Esplosivo - 25-3-2004 at 07:09

Calcium Chloride is a very common dessicant. It can be made as named previously. The calcium chloride solution is then made anhydrous by evaporating off the water and then heating the remaining solid strongly (it usually melts if heated too strongly). It does not decompose during heating, and I can confirm that from experience :P

microwave is the best way to dry drying salts

acx01b - 6-5-2004 at 11:38

microwave is the best way to dry drying salts

try with blue CuCl2: hard with heat to obtain completly white stuff, or you need to heat it for 5-10 min.

with microwave: 30sec

same with CaCl2: when you store it, after 1month it is really far to be dry... it is full of non-cristallized water!!

30sec microwave...

and you get it dried back.

work for 1gr-->10gr not more, or you need to dry it 5min under heat before if you dont want to destroy your microwave.

[Edited on 6-5-2004 by acx01b]

thunderfvck - 6-5-2004 at 23:26

I recently tried to dry my CaCl2 in the microwave and I broke the plate.

The stuff also jumped around wildly and made quite a mess.

Never again. CaCl2 is for the oven only.

I could probably use a better plate, but, nah. Being stubborn is fun.

acx01b - 7-5-2004 at 10:32

If when you heat it it jumps around, it will jump around too in your microwave

lol


thats what i learnt yeasterday trying to dry Na2So4....

but if there is no FREE h2o in your salt, it wont jump around.

microwave is the easiest way (20-30sec 800watt) to get dried MgSo4 from MgSo4.6H2O but if there is more than 6 mole of h2o for 1 mole of mgso4, it will jump around in your microwave and you'll get quite a mess....

to prevent it, you can always cover it with a glass..

I DIDNT GET ANY BROKEN PLATE!!! but i didnt let it more than 5sec when it started to jump around

sorry anyway...... if you broken your plate

praseodym - 25-7-2005 at 05:52

Which will be the best drying agent in a desiccator, MgSO4, Mg(ClO4)2, CaH2 or LiAlH4?

sparkgap - 25-7-2005 at 06:07

I have yet to hear of chlorates being used to dry things, but I can assure you that it is a waste of good hydrides to use them for drying stuff. The hydrides have much more utility than that!!!!

sparky (~_~)

neutrino - 25-7-2005 at 06:21

Actually, Mg(ClO<sub>4</sub>;)<sub>2</sub> is very hydroscopic. IIRC, it is/was used industrially to dehydrate nitric acid.

We need a little background here: what is your budget, how much drying do you have to do, etc.

edit: Oops, the nitrate is used for nitric acid. The perchlorate is still very hydroscopic.

[Edited on 26-7-2005 by neutrino]

Quibbler - 25-7-2005 at 06:41

If you mix blue copper sulphate with dry alcohol you will find that the reaction goes the ther way - the alcohol acts as a drying agent and white anhydrous CuSO4 comes out as a ppt. Oh and in a desicator you can't beat phosphous pentoxide.

bio2 - 25-7-2005 at 15:57

.........Which will be the best drying agent in a desiccator, MgSO4, Mg(ClO4)2, CaH2 or LiAlH4?..................

Depends on how dry you need it and how often you do it.

For general use most commonly used is sulfuric acid or calcium sulfate (dryrite indicating). Dryrites capacity is low but dries more completely than most other powders for general use such as sodium sulfate, MgSO4 etc.

You need to look at the residual moisture and capacity spec to determine what suits the purpose.

praseodym - 26-7-2005 at 05:17

I also believe it should be MgSO4 because the other 3 are simply more dangerous than MgSO4. The 2 hydrides produce hydrogen gas when being used as a drying agent and H2 is flammable. perchlorates, on the other hand, is a strong oxidiser, hence, could be explosive. Am i right?

neutrino - 26-7-2005 at 09:58

Quote:
Originally posted by praseodym
perchlorates, on the other hand, is a strong oxidiser, hence, could be explosive. Am i right?


Yes, if they are mixed with combustibles.

Rock salt

MadHatter - 26-7-2005 at 16:18

I find that plain old rock salt is more than adequate for drying out ethanol. Besides, drying
the NaCl out in an oven is very fast at 300 F. This is a popular method for those making
their own gasohol.

12AX7 - 26-7-2005 at 17:09

Howso? NaCl can only adsorb and occlude moisture (or ethanol for that matter), it doesn't hydrate except under pressure.

Tim

neutrino - 26-7-2005 at 17:35

It sounds like salting out to me. Add salt to an alcohol/water mixture and you get one layer of alcohol and one of salt water.

Rosco Bodine - 28-7-2005 at 10:37

Immerse some chunks of scrap aluminum in a moderately strong solution of
NaOH or spray with oven cleaner and then rinse , and immerse in dilute HCl .
Then amalgamate the aluminum fairly heavily by adding some mercuric chloride to the dilute HCl . When the surfaces are
very well plated with a mirror of liquid mercury , and evolving hydrogen freely ,
the chunks of amalgamated aluminum are removed and shaken free of excess liquid . The amalgamated Al chunks will
make a very active dessicant and deoxygenation reagent . The amalgam
should pull a partial vacuum within a closed dessicator as the Al binds with any moisture and oxygen in the confined space , therefore some sort of valve for
a vacuum release will facilitate opening the dessicator later . The Al will be consumed and converted to a powder emerging from the film of mercury as the
reaction proceeds .

garage chemist - 28-7-2005 at 12:45

That would be very useful indeed, were it not for the nastiness of mercury.

There once was a concept for a hydrogen generator for a fuel cell car which relied on the reaction of amalgamated aluminium with water.
The idea had to be abandoned because the exhaust gasses from the fuel cell drastically exceeded every safe level for mercury vapors! :o

Rosco Bodine - 28-7-2005 at 14:24

You can recover most of the mercury by simply dissolving the residue in HCl , leaving a small globule of mercury at the
bottom of the AlCl3 solution . The AlCl3 solution can be kept for other uses , such as being the precursor for Aluminum Chlorophosphate refractory binder , after treatment with phosphoric acid .

praseodym - 30-7-2005 at 03:12

If it is for drying the atmosphere, would magnesium sulphate or magnesium perchlorate be a better drying agent?? Is magnesium sulphate only used to dry organic substances??

UnintentionalChaos - 16-12-2006 at 00:43

Holy crap. I wish somebody would have warned me about MgSO4 fusing together like that. I dried about 500g of it in the oven in a small casserole dish and it took several minutes of chiseling to get underneath an edge and pry the block up. :o I wish I could get anhydrous isopropanol here but it only comes with 30% water. Still, it is much easier to get than ethanol (underage still, or id go buy vodka). So that leads me to drying out isopropyl with MgSO4. The epsom salts are dirt cheap from the pharmacy so I like the idea of using it as a dehydrating agent.
Also, Saerynide mentioned before about how you can get CaCl2 from room dehumidifiers. If you look around in hardware stores or even supermarkets, you may be able to find pure CaCl2 for use as road de-icer. It looks exactly like the stuff in the room dehumidifiers (the way its pelletized) so I assume they may have bought it from exactly the same chemical company, but I can get 4 1/2 kg of it for $8 (US) instead of maybe 300g maximum from a dehumidifier for $2.80.
Another idea for cheap solvents is n-heptane. I don't know if its properties differ drastically from benzene, but it makes a nifty nonpolar solvent. Look in art supply stores. It is used as rubber cement thinner. Not terribly easy to find because many other products are marketed that contain some n-heptane or petroleum distillates that do the same thing. The art supply store near my college campus carries it at a liter for $6 (US). They also have turpentine, but I'm not particularly sure how useful that might be.

cnidocyte - 2-2-2011 at 08:08

Can you dry polar solvents with MgSO4 and other common drying agents? I was under the impression that drying agents absorb all polar liquids making them suitable only for drying non polar liquids. Is this how it is or do these drying agents selectively absorb water?

Rogeryermaw - 3-2-2011 at 00:23

how well would MgSO4 work in a tube for drying gasses such as NH3 and Cl2? i was looking to generate chlorine from TCCA + HCl and NH3 from NH4NO3 + NaOh. if not, what would be ideal for this purpose?

Arthur Dent - 3-2-2011 at 05:02

I've tried the "gradual heating" method with sodium bi to turn it into carbonate and it worked. Starting with a 500g pack of Cow Brand in a pyrex plate, I started with the plate in the regular oven for one hour at 150F, then stirred its content, then 1h at 200F, and again 1h at 250F and so on, and 7 hours later, I had substancially less material but it did not congeal into one solid mass, it remained fluffy powdery (probably because of the constant stiirring).

So I was wondering if that smooth, gradual heating method with constant stirring would work with plain old epsom salt to make it somehow anhydrous without turning it into a solid rock? For now, my official "dessicator" apparatus is a large ziploc bag with a dollar store CaCl2 damp trap, but I do intend to upgrade to a real vacuum dessication apparatus soon (maybe tomorrow)... so I'll need a selection of efficient drying agents.

Robert

ScienceSquirrel - 3-2-2011 at 05:20

Sodium bicarbonate loses water and carbon dioxide and the carbon dioxide keeps it fluffy, the soda ash formed is very fine indeed.
Epsom salts is a hydrate and tends to melt in its own water of crystallisation.
I think if you warmed it slowly it would start to effloresce to form the monohydrate which would then form a fluffy powder.
Here are the melting points;
http://en.wikipedia.org/wiki/Epsom_salt
I would try 120 to 130 until I was sure that quite a lot of water had been lost and then 175 - 190 and then heat it up to 250 -300 C to finish the job.
You can use a set of lab scales to follow the dehydration, I have checked on the complete decomposition of sodium bicarbonate using scales. Do not forget to let the sample cool before weighing.

mr.crow - 3-2-2011 at 09:34

Quote: Originally posted by Arthur Dent  

So I was wondering if that smooth, gradual heating method with constant stirring would work with plain old epsom salt to make it somehow anhydrous without turning it into a solid rock? For now, my official "dessicator" apparatus is a large ziploc bag with a dollar store CaCl2 damp trap, but I do intend to upgrade to a real vacuum dessication apparatus soon (maybe tomorrow)... so I'll need a selection of efficient drying agents.


CaCl2 and NaOH are great for desiccators, very hygroscopic. NaOH also absorbs acid fumes. I'm not sure how well MgSO4 works in this application so I don't think its necessary. Just for drying organic solvents.

Don't worry about turning into a solid rock, its breaks apart easily. Put it in a ziplock bag and use a hammer or blocks of wood.