Sciencemadness Discussion Board

Solute for Metal oxides

veerenyadav - 22-5-2017 at 19:14

Is there any solute which can dissolve metal oxides ( Fe2O3,MOx, etc) but not as ions ?

j_sum1 - 22-5-2017 at 19:35

I think the word you want is solvent.

Yes. Water is pretty good. you can dissolve Na2O and K2O in water pretty easily.
But I suspect that is not the answer you were after.

veerenyadav - 22-5-2017 at 19:39

Both your points are correct. I am searching for a solvent and but it should not dissolve the oxide in the form of ions rather molecules .

Thanks

j_sum1 - 22-5-2017 at 21:11

Well your problem right there is that most metal oxides are not molecular. There are exceptions. Osmium tetroxide springs to mind.
Let's think electronegativities here. Oxygen is the second most electronegative element. And metals are by definition those elements that are less electronegative. Forming a bond between them is therefore going to involve a large difference in electronegativities which, again by definition, means you are generally going to referring to an ionic bond rather than a covalent bond. And with ionic bonds you are going to get an ionic lattice and dissociation into ions when dissolved. You are not going to get molecules.

Of course there are exceptions. (Aren't there always?) For example the OsO4 I mentioned before. But in general your answer is going to be No. Metal oxides do not dissolve in anything in a molecular form.

Curious. What inspired this question? It strikes me as a weird one.

DraconicAcid - 22-5-2017 at 21:16

Since these oxides are not molecular, it will not happen.

Harristotle - 23-5-2017 at 02:11

I disagree.
Iron oxides/hydroxides are frequently polymers, and the oxo-iron-oxo bonds are more covalent than ionic in nature. EXAFS and other studies have shown this. Acid will depolymeris/ionise them to ionic form, but at high pH they are definitely not ionic..

Apparently there are other metals like this also. I don't have my old texts, but I recall xray diffraction photos of iron oxide as forming rings, not spots - no regularity to that lattice!
Admittedly, the iron oxide was ferrihydrite from the protein ferritin.


This is suggested by this paper http://pubs.acs.org/doi/abs/10.1021/la00013a046 , the first that I lazily found. I was supprised to see Cr and Al mentioned as other suspects too.

Cheers, H.

Eddygp - 23-5-2017 at 02:50

Molecular or not, the thing is, except for osmium tetroxide, there is no single molecule of "Fe2O3", it is a reduction of the stoichiometric proportion of atoms in the crystal. The problem is that it is a crystal.
In the same way as you can't dissolve high-density polyethylene in hexane in spite of it being basically the same thing, this is even more pronounced for metal oxides. The whole lump kind of is "the" molecule. SOlvation cannot break the crystal apart (and if it did at all, it would be some kind of hydrated iron complex, and certainly only in the presence of an anion from an acid or something).

kmno4 - 23-5-2017 at 03:52

The answer is : ionic liquids.
Many 'insoluble' oxides (CuO, Fe2O3, Cr2O3, Al2O3, MnO2....) are soluble in such solvents.
As far as I remeber, adequate article was mentioned (or posted) somewhere on the board.

Dan Vizine - 23-5-2017 at 10:16

Soluble has different connotations depending upon what your intention is. For example, what is called soluble for spectroscopic purposes is not always what you'd call soluble for preparative purposes. If you're trying for a very high solubility, or even a moderate one, it's not going to happen with most of these oxides.

DraconicAcid - 23-5-2017 at 11:23

Quote: Originally posted by kmno4  
The answer is : ionic liquids.
Many 'insoluble' oxides (CuO, Fe2O3, Cr2O3, Al2O3, MnO2....) are soluble in such solvents.
As far as I remeber, adequate article was mentioned (or posted) somewhere on the board.


Choline chloride-based ionic liquids will dissolve such oxides, but not as molecules.

The only time you'll get molecules of a metal oxide is when the metal is in a very high oxidation state- CrO3, Mn2O7, OsO4. For things like Fe2O3, Al2O3, MnO2, etc, the bonding is network covalent. The bonds are covalent, but you don't have individual molecules. you have one massive macromolecule instead, and the only way to dissolve it is to rip it into bits, effectively ionizing it.

Does it mean polymeric oxides ......

veerenyadav - 24-5-2017 at 19:29

Thanks for putting wonderful perspectives.

(A) Does it mean that polymeric oxides ( Si, Ca, Na,... ) can be dissolved in a solvent ?

(B) Can these oxides dissolve in the from of nano particles ?


violet sin - 24-5-2017 at 22:58

- veerenyadav
" it should not dissolve the oxide in the form of ions rather molecules ."

- J_sum1
- "Well your problem right there is that most metal oxides are not molecular"

- DraconicAcid
- "Choline chloride-based ionic liquids will dissolve such oxides, but not as molecules"

____________
I losely use DES /IC interchangeably below, DEEP eutectic solvent and ionic liquid, referring to a non-standard solvent. Also not citing specific examples so I hope it's not to incorrect .
____________

It doesn't dissolve them as Fe +++ and O - -, but it doesn't necessarily dissolve them as the empiracle formula either.

the metal oxides would be dissolved in a manner similar to soap and grime, no? Correct me if I'm wrong, personally I saw it as an encapsulation by units of a charged or electronic nature, affecting things like lone pairs and disrupting bonds that are normally favored. promoting solovation by making the aggregate unit cluster( metal oxide/ionic liquid/DES sheath) more favored than a solid complex of oxide. More of a masking the electronic nature of the units from one another and moderating the difference between dissolved substance and neat solvent. There would be a point at which the disguise could no longer fool the solid or solution based on size.

If the attraction was as that, dissolved unit complexes could be "watered down" with extra ionic liquid to ensure total dissolution on a level determined by geometry of the charge at an atomic scale. Something on the order of small numbers of metal oxide unit conglomerates are easily envisioned, surrounded by the moderating cloak of bound and associated DES(deep eutectic solvent) which may not have the ability to separate more fully. Or perhaps it goes all the way down to metal oxide units for some. Don't know. But *I bet* it would be safe to say they *could be on nano scale before solvent could no longer peel bits off and hide them effectively. Safer to say the bits are very small if not empirical .

For reference

"Nanoparticles are particles between 1 and 100 nanometers in size"
https://en.m.wikipedia.org/wiki/Nanoparticle
Wiki

"The thing is, atoms are very, very small, but they still have a finite size. A hydrogen atom, for example, is about 0.1 nanometers, and a caesium atom is around 0.3nm "
https://www.extremetech.com/computing/97469-is-14nm-the-end-...
-Is 14nm the end of the road for silicon chips?

__________________
This looks interesting, and maybe worth chasing down...
____
http://pubs.acs.org/doi/abs/10.1021/jp0642995?journalCode=jp...
==Task-Specific Ionic Liquid for Solubilizing Metal Oxides
"Protonated betaine bis(trifluoromethylsulfonyl)imide is an ionic liquid with the ability to dissolve large quantities of metal oxides. This metal-solubilizing power is selective. Soluble are oxides of the trivalent rare earths, uranium(VI) oxide, zinc(II) oxide, cadmium(II) oxide, mercury(II) oxide, nickel(II) oxide, copper(II) oxide, palladium(II) oxide, lead(II) oxide, manganese(II) oxide, and silver(I) oxide. Insoluble or very poorly soluble are iron(III), manganese(IV), and cobalt oxides, as well as aluminum oxide and silicon dioxide. The metals can be stripped from the ionic liquid by treatment of the ionic liquid with an acidic aqueous solution."

_________
http://pubs.acs.org/doi/abs/10.1021/je060038c
==Solubility of Metal Oxides in Deep Eutectic Solvents Based on Choline Chloride
"The solubility of 17 commonly available metal oxides in the elemental mass series Ti through Zn have been determined in three ionic liquids based on choline chloride. The hydrogen bond donors used were urea, malonic acid, and ethylene glycol. The results obtained are compared with aqueous solutions of HCl and NaCl."

j_sum1 - 25-5-2017 at 00:53

VS. Thorough answer to what was a vague question.

Nice to have some specific detail on a DES and what it dissolves. I don't know the scale of the solvated units or whether they match the OP's concept of a molecule. But these kinds of posts and referenced are gold.

Thanks.

DraconicAcid - 25-5-2017 at 08:08

Quote: Originally posted by violet sin  

I losely use DES /IC interchangeably below, DEEP eutectic solvent and ionic liquid, referring to a non-standard solvent. Also not citing specific examples so I hope it's not to incorrect .
____________

It doesn't dissolve them as Fe +++ and O - -, but it doesn't necessarily dissolve them as the empiracle formula either.

the metal oxides would be dissolved in a manner similar to soap and grime, no? Correct me if I'm wrong, personally I saw it as an encapsulation by units of a charged or electronic nature, affecting things like lone pairs and disrupting bonds that are normally favored. promoting solovation by making the aggregate unit cluster( metal oxide/ionic liquid/DES sheath) more favored than a solid complex of oxide. More of a masking the electronic nature of the units from one another and moderating the difference between dissolved substance and neat solvent.


If you dissolve a metal oxide in an ionic liquid, the ions of the liquid are surely going to react with those of the metal oxide. Chlorides from the choline chloride will coordinate to the metal ions. The oxide ion is a very strong base, and will deprotonate other components of the melt. If you dissolve Fe2O3 in choline chloride/malonic acid, you will get iron ions coordinated by chlorides, hydroxides, and malonates.

DraconicAcid - 25-5-2017 at 08:19

Quote: Originally posted by veerenyadav  
Thanks for putting wonderful perspectives.

(A) Does it mean that polymeric oxides ( Si, Ca, Na,... ) can be dissolved in a solvent ?


Calcium and sodium oxides are simply ionic, and not polymeric. the only solvents that they may dissolve in without reacting are simple molten salts such as alkali halides, hydroxides, or nitrates. Sodium oxide would surely deprotonate organic components of low-temperature melts containing choline ion, urea, malonic acid, etc.

chornedsnorkack - 26-5-2017 at 23:04

Precisely how is, for example, NaOH dissolved in C2H5OH?
Ethanol is a weak acid. Therefore the reaction
NaOH+C2H5OH<->C2H5ONa+H2O
should be reversible. You could produce ethoxysodium, and then recover NaOH by reversing the reaction.
Does ethoxysodium dissolve in ethanol?
If yes, how?
Ethanol has dielectric permitivity lower than water. About 24, while water has 80.
Does ethoxysodium not dissolve in ethanol, or dissolve as ions, or dissolve as undissociated ethoxysodium molecules?

DraconicAcid - 27-5-2017 at 07:55

Sodium ethoxide will dissolve in ethanol as ions. Because of the low dielectric constant, the ions will be paired, but there will be no covalent bond between the sodium and the ethoxide (and thus, not a molecule).

chornedsnorkack - 27-5-2017 at 10:40

Do micelles count as nanoparticles?

veerenyadav - 28-5-2017 at 08:03

Thanks to all

But if metal oxides remain as macromolecules in solid form then what happen these oxides get melted .

I mean still macrocrystal or single molecules ?
Or
What is blend of metal oxides melted togethor ?

DraconicAcid - 28-5-2017 at 08:55

Quote: Originally posted by veerenyadav  

But if metal oxides remain as macromolecules in solid form then what happen these oxides get melted .

I mean still macrocrystal or single molecules ?

When a covalent network metal oxide gets melted, it breaks down into smaller macromolecules and large polyatomic ions.

chornedsnorkack - 28-5-2017 at 09:18

How polar are transition metal acetates?

DraconicAcid - 28-5-2017 at 10:54

Quote: Originally posted by chornedsnorkack  
How polar are transition metal acetates?

They are generally ionic, so asking how polar they are is a non sequitur. How ionic they are will depend on the oxidation state of the metal.

chornedsnorkack - 28-5-2017 at 12:02

Quote: Originally posted by DraconicAcid  
Quote: Originally posted by chornedsnorkack  
How polar are transition metal acetates?

They are generally ionic, so asking how polar they are is a non sequitur. How ionic they are will depend on the oxidation state of the metal.


It is not non-sequitur.
Iron(III) forms a trinuclear complex, roughly Fe3O(CH3COO)7.
That turns out to be insoluble in water... but soluble in ethanol.
Being soluble in ethanol but not water hints at low polarity.
Also: although acetic acid is a stronger acid than ethanol, it is surprisingly low polarity. While the dielectric permittivity of ethanol is 24, that of acetic acid is just 6,21.
The dielectric permittivity is quoted to be 27 at 80 % acetic acid by weight, 20 % water.
So, is concentrated acetic acid a good solvent for low polarity solutes? Such as molecular acetates?