Sciencemadness Discussion Board - Miscible verses Solubility

Miscible verses Solubility

Craftbrewer - 12-11-2014 at 15:16

In my continued experiments with separating denatured ethanol, I cant wrap my head around what happens with compounds that are miscible and soluble in a mixed solution.

Picture say oil on water, and a compound that is soluble in one to a certain level, BUT miscible in the other. How does one determine where equilibrium is reached. Does the miscible liquid "absorb" past the normal solubility of the other liquid?

I would guess there is a point that the soluble liquid will hold onto a certain level of a compound that is soluble, and if that is correct, what determines that level.

Just trying to wrap my poor brainbox around the concept.

aga - 12-11-2014 at 15:58

'Miscible' means they just Mix nicely.
No reactions going on.

'Soluble' means that one of them disassociates into the other.

One of them breaks up, and becomes Ions of the bits it was made of.

Basically Table Salt is no longer Table salt when you dissolve it in water.

Craftbrewer - 12-11-2014 at 16:03

yep, BUT that doesn't answer the question as to what determines the equilibrium between the two.

Is it how soluble a compound is, or maybe a simple volume split. ie have equal volumes of each, therefore the solution drops by half.

Just don't know

aga - 12-11-2014 at 16:18

I guess that's cos i don't know.

If you have two imiscible liquids, then they form 2 layers.

Add another substance XY that is soluble in one layer, also miscible in the other, then there should be an equilibrium of mixed XY in one layer, and X+ Y- in the other layer, and an exchange at the interface of the two layers, giving an overall equilibrium.

At a total Guess, it would depend on how soluble it is in the layer it likes to be soluble in.

If it's pKwas anywhere near 1, it would essentially always be disassociated in the soluble layer, meaning that there would eventually be no XY available to get mixed, as it would all be dissolved all the time.

Metacelsus - 12-11-2014 at 17:38

https://en.wikipedia.org/wiki/Partition_coefficient

macckone - 12-11-2014 at 18:42

Quote: Originally posted by aga

'Miscible' means they just Mix nicely.
No reactions going on.

'Soluble' means that one of them disassociates into the other.

One of them breaks up, and becomes Ions of the bits it was made of.

Basically Table Salt is no longer Table salt when you dissolve it in water.

Miscible means liquids mix nicely.

Soluble means that only a limited amount of a substance will
dissolve in a liquid. Disassociation is not required. Especially
in non-polar solvents where an ionic material would not be
significantly soluble. Example: hydrogen chloride is soluble in
benzene but it does not disassociate. Benzene is also
minimally soluble in water but does not disassociate.

Cheddite Cheese provided an excellent answer to the
original question as I understand it.

Ozone - 12-11-2014 at 18:48

SFAIK, "miscible" means that they mix together in all proportions without forming two phases. There are many things that are soluble--up to a point, when they separate. Both phases still contain considerable parts of each.

O3

Chemosynthesis - 12-11-2014 at 18:54

It gets really complicated. See also:
http://en.wikipedia.org/wiki/Solubility_equilibrium

Hildebrand is also a name that is valid.

DraconicAcid - 12-11-2014 at 19:35

Quote: Originally posted by aga

'Soluble' means that one of them disassociates into the other.

One of them breaks up, and becomes Ions of the bits it was made of.

Nonsense. 'Soluble' simply means there's a limit to how much solute will dissolve in a given solvent. Many non-electrolytes are soluble (at least to some extent) in water- sucrose, glucose, butanol, etc., without being miscible or ionizing.

aga - 14-11-2014 at 02:10

Quote: Originally posted by DraconicAcid

Sorry. My ignorance shining though again.

Craftbrewer - 14-11-2014 at 13:27

well

with a little more research, and the references given, I think (but not confident) that the answer is a simple volumetric dilution. In other words, neither liquid has a greater attractive or repulsive power than the other.

or

Have compound x that is soluble in a solution, add another equal volume of a solution that its miscible to compound x, then each will have 1/2 the amount of compound x.

hope this makes sense

Chemosynthesis - 14-11-2014 at 13:38

Another way I was taught to view solubility, in keeping with attractive/repulsive forces deals with entropy; for solids, if the entropy gain is enough to offset the lattice enthalpy at a given temperature, you get dissolution. Same with liquid interactions in that entropy can be mazimized between water and oils, for example, by minimizing the surface area of interaction and forming two relatively distinct phases depending on whether there is a strong enough difference in attraction between molecules of solvent with itself vs. solute. And please don't ask about which is which in an equivolume mix or whatever because I don't know.
Edit: the maximization of entropy is through things such as rotational excitatory states not accessible to solvating molecules forming a hydration shell, since they are limited in pointing direction due to attractive forces (hydrogen bonds/dipole interactions). Reverse this when breaking such interactions between a homogenous fluid. Whichever scalar is larger predicts spontaneity. This helps envision why solubility can change with temperature too.

[Edited on 15-11-2014 by Chemosynthesis]

DraconicAcid - 14-11-2014 at 16:05

Quote: Originally posted by Craftbrewer

Have compound x that is soluble in a solution, add another equal volume of a solution that its miscible to compound x, then each will have 1/2 the amount of compound x.

Not really, because the solute will be more soluble in one solvent than in the other, particularly if it's miscible in one and merely soluble in the other.

Magpie - 14-11-2014 at 16:23

I'm not sure if this is the answer you are looking for but I think the root answer is that the system (the phases) adjusts itself until the delta chemical potential (delta Gibb's free energy) is zero. Chemical reactions that reach equilibrium do that too.

Blogfast, deltaH, or Chemosythesis can probably tell us more about that.

[Edited on 15-11-2014 by Magpie]

Etaoin Shrdlu - 14-11-2014 at 19:16

Quote: Originally posted by DraconicAcid

Quote: Originally posted by Craftbrewer

Have compound x that is soluble in a solution, add another equal volume of a solution that its miscible to compound x, then each will have 1/2 the amount of compound x.

Not really, because the solute will be more soluble in one solvent than in the other, particularly if it's miscible in one and merely soluble in the other.

If the solvents are both miscible with Compound X, they're probably miscible with each other.

DraconicAcid - 14-11-2014 at 23:15

Quote: Originally posted by Etaoin Shrdlu

If the solvents are both miscible with Compound X, they're probably miscible with each other.

Not always. Acetone, I think, is miscible with most organic solvents (such as hexane, benzene, toluene, etc.) and it's miscible with water. Water isn't miscible with hexane, benzene, toluene, etc.

deltaH - 15-11-2014 at 00:14

There are many ways to approach phase equilibrium problems. Chemical engineers tend to prefer working with fugacities but is not straightforward for a beginner... it's typically taught as part of a semester thermodynamics course at undergrad level.

You can solve phase equilibrium problems by starting with the 'rule' that the fugacity of each component in each particular phase is equal to its fugacity in every other phase in which it is in equilibrium with (if I didn't muck that up). You then plug in the equations for these fugacities from a thermodynamics textbook and make as many simplifications as apply and then solve the equations.

In the case of solids dissolving in liquids and also in liquid-liquid systems, the 'activity coefficient' and the model used to calculate it often becomes very important (but activity coefficients can be approximated to equal 1 and so ditched in certain cases). It is this activity coefficient that describes the non-ideal behaviour, for example that of excess heats or heats of mixing and also the phenomenon of two liquids not fully mixing.

Anyhow, this is a very long story that I cannot describe in a few paragraphs, but I reffer you to a good thermodynamics text, such as chapters 8-13 of http://www.amazon.com/Chemical-Biochemical-Engineering-Therm...

This is what I used when I was a student... an excellent text.

[Edited on 15-11-2014 by deltaH]

Magpie - 15-11-2014 at 07:17

Thank you deltaH for that concise and informative introduction to this truly hairy subject - I didn't want to touch it - it's been too many years since I took chemical engineering thermodynamics in college. My text was the one by Smith & Van Ness.

blogfast25 - 15-11-2014 at 07:42

Quote: Originally posted by Magpie

I'm not sure if this is the answer you are looking for but I think the root answer is that the system (the phases) adjusts itself until the delta chemical potential (delta Gibb's free energy) is zero. Chemical reactions that reach equilibrium do that too.

Yes. Partitioning equilibria follow basically the same rules as chemical equilibria. Gibb's free energy is the driver. ΔG becomes zero at equilibrium.

Etaoin Shrdlu - 15-11-2014 at 10:42

Quote: Originally posted by DraconicAcid

Quote: Originally posted by Etaoin Shrdlu

If the solvents are both miscible with Compound X, they're probably miscible with each other.

Not always. Acetone, I think, is miscible with most organic solvents (such as hexane, benzene, toluene, etc.) and it's miscible with water. Water isn't miscible with hexane, benzene, toluene, etc.

True. Acetone is miscible with every solvent I've ever used. Small oxygen-containing molecules are jerks.

Practically, though, there are way more solvent combinations that don't show this behavior than those that do. If you pick X and Z randomly from "solvents miscible with Y," it's pretty likely that they're going to be miscible with each other as well.

If not, then you wind up with the same problem you'd have when Y is only soluble, with the added wrinkle that it's now more likely adding your solute Y will result in everything going into one homogeneous solution.

chornedsnorkack - 15-11-2014 at 12:21

Quote: Originally posted by Etaoin Shrdlu

Quote: Originally posted by DraconicAcid

Quote: Originally posted by Etaoin Shrdlu

If the solvents are both miscible with Compound X, they're probably miscible with each other.

Not always. Acetone, I think, is miscible with most organic solvents (such as hexane, benzene, toluene, etc.) and it's miscible with water. Water isn't miscible with hexane, benzene, toluene, etc.

I wouldn´t classify it so.
I think that polarity series or something might be useful to estimate the expected miscibility of various solvents. For example water and diethyl ether are far enough that they have appreciable but limited mutual solubility and are not miscible. Ethanol is between water and ether, and is close enough to both to be miscible with both. Add fairly modest amount of ethanol to water and ether, and you get a solution of both in ethanol.

Now, take the original question: say you have water and 1-octanol. These are immiscible, with little solubility (I think 0,5 g 1-octanol in 1 l water).
Now take another solvent, which is fairly soluble but not miscible in water, and is miscible in 1-octanol. For example 1-butanol: solubility 73 g 1-butanol in 1 l water - much more soluble than octanol, but not miscible.
Now what do you want to predict?

Etaoin Shrdlu - 15-11-2014 at 14:40

Quote: Originally posted by chornedsnorkack

I wouldn´t classify it so.

As a jerk? Small oxygen-containing molecules have bizarre discrepancies in solubility parameters from what one would project just comparing them to the heavier organic solvents. Hence, my incredibly scientific terminology. Daft things. EDIT: Ahhhh, Flory-Huggins theory. I thought it had a name. Apparently, small hydrocarbons do the same thing, but needless to say I don't do a lot of shaking propane with ethanol and eyeballing the solution.

Quote: Originally posted by chornedsnorkack

I think that polarity series or something might be useful to estimate the expected miscibility of various solvents. For example water and diethyl ether are far enough that they have appreciable but limited mutual solubility and are not miscible. Ethanol is between water and ether, and is close enough to both to be miscible with both. Add fairly modest amount of ethanol to water and ether, and you get a solution of both in ethanol.

Yep. Hansen's Solubility Parameters relate solubility to dispersion forces, polarity, and hydrogen bonding capability. They're measurements, not something derived from a formal theory, but useful, and yes, there are expected trends in there.

[Edited on 11-16-2014 by Etaoin Shrdlu]

aga - 16-11-2014 at 14:16

Quote: Originally posted by aga

Edit:

This is wrong. Ignore this answer