hydroxides for drying

[b159510]

Can anyone explain to me how a metal hydroxide, like NaOH, reacts to remove water?

I have never heard of a metal hydroxide being used to dry liquids. My list of 38 drying agents does not include any hydroxides.

Sodium and potassium metal dry liquids by forming the metal hydroxides and hydrogen gas, this I know.

Digging through my vast private library, I uncovered an organic lab text from 1950 that calls for the use of NaOH pellets to dry N-Methylpyrrole.

Is this simply an ion solubility question?

[EDIT] maybe ion solubility wasn't the right term. In an
excess of NaOH, there would be a continuous reaction between
OH- and water. But water will always be present. Does this
reaction tie up the water, thus removing it from the organic
liquid?

thanks
Back to the Primitive

[lugh]

What you need to do is leave some sodium hydroxide crystals out in a humid atmosphere and observe what happens, the term is hygroscopic    Drying agents are classified as either physical or chemical. Chemical agents are classified as hydrate forming salts, oxides, acids, bases (caustics) and metals. Caustics are the best agents for drying amines, if this fact isn't apparent in your library, you need to consider an expansion plan  

[b159510]

hahaha,... give me a break dude.
Back to the Primitive

[b159510]

gee. well at room temp i guess if you have 1 mole NaOH and 1 mole water, you could get a hydrate of sorts. 1 mole NaOH and 2 moles water, you get dissolved NaOH. how sweet

Back to the Primitive

[lugh]

give me a break dude.

Well, what I don't understand is why a so called "professional student" can't take some initiative and make their way to the library to do their own research, it's good to get a little exercise    Adsorption is a surface phenomena, the interface is the solid NaOH and the water present in solution. As the process advances, a layer of NaOH saturated water can be observed. If you would have done the simple experiment as I asked, you would have observed the crystals adsorbing the water from the air, and as you may have heard, "a picture is worth a thousand words". CRC doesn't list a hydrate, so the process you've theorized is probably not the case. I imagine hydrogen bonding is at work (big surprise }, the equilibrium is driven toward a saturated solution.

[Osmium]

> gee. well at room temp i guess if you have 1 mole NaOH
> and 1 mole water, you could get a hydrate of sorts. 1
> mole NaOH and 2 moles water, you get dissolved NaOH.
> how sweet

What if you have 5 moles of NaOH and 1 mole of H2O? Where will the water go preferentially? Into the organic or into the inorganic substance? Will an aqueous solution of NaOH form? Or will the NaOH remain a solid even though it has 20% water absorbed? Can the NaOH be removed by decantation/filtration? What do you think?

[b159510]

no shit lugh. i dont need to do the 'experiment' because
i've seen it a hundred times. i understand what adsorption
is, and hydrogen bonding. i would say f ckoff,
but i'll just say goodbye.
Back to the Primitive

[lugh]

no shit lugh. i dont need to do the 'experiment' because i've seen it a hundred times. i understand what adsorption is, and hydrogen bonding. i would say
f ckoff, but i'll just say goodbye.

Whatever floats your boat

If you knew the answer, why start this thread? If you believe there are only 38 drying agents known to organic chemists, you need to expand your horizons    Hydroxides have been used as drying agents for almost two centuries, this fact isn't exactly the breakthrough of the century  

[b159510]

What if you have 5 moles of NaOH and 1 mole of H2O? Where will the water go preferentially water will be drawn out of the organic. i doubt you would be able to decant it or filter it. there would be dissolved and undissolved NaOH. well you could decant off most of the organic if it was something like ether or toluene.
Back to the Primitive

[b159510]

whatever - i use what's used in the labs. in the four
years i've been working in the lab, no person has ever used
a hydroxide to dry a liquid. the only mention of using
NaOH as a drying agent i have seen is in a 50 year old
lab text. have to keep an open mind though, and remember
how things used to be done. i understand how it works,
doesn't seem like a particularly attractive method, but
if it works - it works.
Back to the Primitive

[Osmium]

> water will be drawn out of the organic.

Yes.

> i doubt you would be able to decant it or filter it. there
> would be dissolved and undissolved NaOH.

No. There won't be any liquid NaOH.
Example: commercial KOH is 85%, a few (maybe 2 or 3) % K2CO3, rest water. Yet it is a solid.

> whatever - i use what's used in the labs. in the four
> years i've been working in the lab, no person has ever
> used a hydroxide to dry a liquid.

I've seen KOH being used to dry solvents repeatedly, even though it already contains up to 15% of water. Someone I know used KOH/CaCl2 effectively to dry huge amounts of acetone/THF mixture used in flash chromatography, having a 6L distillation unit running up to 12 hours a day for solvent recycling. It definitely works.

[terbium]

. i would say fckoff, but i'll just say goodbye.

Promises, promises ...

[timsong]

Ref:

Sodium Hydroxide forms hydrates with 7,5,4,3.5,3.11,2(mp 12.7c)and 1(mp 64c)H2O, and potassium hydroxide with 4(mp -32.7c),2(mp 35.5c),1.5 and 1(mp 143c)H20 (Pickering, JCS., 1893, 63, 890)

There's the facts !!!!!

[Buster_Hymen]

>Digging through my vast private library,

Hey b159510:

I bet if you tossed all the Dr. Suess books, that library of yours would suddenly look ALOT smaller...  
  \\|//
    ô¿ô      --  Semper ubi _sub ubi!
    \O/
      '''

[b159510]

timsong- thanks for the Ref.

Buster- Everyone knows Dr. Suess (god rest his soul)
        was a genius. You'll have to sweeten your offer
        if you want to get those flippers on my collection.

                       
Back to the Primitive

[Osmium]

Who is Dr. Suess?

[terbium]

You really don't know!? Is he not known outside the US?

[Osmium]

No, I don't know him.

But I found out what they were talking about after I considered buster's spelling problems (it's either pulchritude or brains, can't have both    except in very rare cases like mine)

[lugh]

Who is Dr. Suess?

A very famous author of children's books. Should be some info at amazon.com  

[Buster_Hymen]

"Green Eggs and Ham" is a classic, a "must-read". Every civilized person should have this book in their library. I'm sure the pulchritudinous b159510 would agree with me on this one.
  \\|//
    ô¿ô      --  Semper ubi _sub ubi!
    \O/
      '''