Solubility?

Hello, first post here. :)

Anyway, I'm very confused by the concept of solubility.

I realize that the solute is what GETS dissolved, and the solvent is WHAT dissolves, but the concept of a 'solution' doesn't really make sense to me. Why is it a solution and not just a mixture? Is there something unique about it? (is it that it's just a homogenous mixture?)

What role does entropy play in solubility?

What [b]is[/b] solubility? :? :(

I also don't get how something can be [i]miscible[/i]. How can something be a solvent and a solute if miscible substances 'are soluble in one another'?

And solvation... I don't really know what it means.

I realize this is a huge list of questions but if someone could kindly point out an overview of this topic (a web link would be helpful) in plain English, I would really appreciate it..

Generally I understand this stuff with a clear explanation, but unfortunately textbooks don't always offer that. :(

Thanks in advance for the help.

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[color=darkgreen]The analogy that I always use for chemistry students when I'm explaining solubility to them is that the [b]solute[/b] is like Kool-Aid powder. The [b]solvent[/b] is like the water that you use to make the Kool-Aid. The [b]solution[/b] is the final product that you drink, ie, the Kool-Aid.

Entropy increases when disorder increases (Second Law of Thermo), so if a solid was dissolving into water to form a solution, then there would be more ions floating around. For example, you can take a solid chunk of table salt (NaCl). The structure is arranged in such a manner that the molecules are basically locked into place and would have a very difficult time moving. When you dissolve something, the ions form (both Na+ and Cl-), thus creating more things moving around and more disorder.

I hope this helps, and I would have responded sooner, but I was on away and then had to get ready for AP testing. [url=http://www.101science.com/Chemistry.htm]Here[/url] is a list of all sorts of chemistry resources, but you'll have to sort it out to find what you're looking for. Unfortunately, the other site I would have sent you to isn't working right now.[/color]

Thanks! That definitely helped. :D

Also, thanks for that link.

Right now I'm studying acids and bases and I'm rather confused as to why certain species are Lewis acids or Lewis bases. (Why is CO2 considered a Lewis acid if it has lone electron pairs on the central C atom?)

[quote="or3n"]Thanks! That definitely helped. :D

Also, thanks for that link.

Right now I'm studying acids and bases and I'm rather confused as to why certain species are Lewis acids or Lewis bases. (Why is CO2 considered a Lewis acid if it has lone electron pairs on the central C atom?)[/quote]
Oxygen is more electronegative than Carbon, therefore there will be a delta positive charge on the carbon and a delta negative charge shared on the two oxygens - overall there is no dipole, because it is symmetrical, but the carbon is still slightly positive, that is, electron defficient, therefore a lewis *acid*

[color=darkgreen]Also, if water is added to carbon dioxide, carbonic acid (H2CO3) will form, which is the whole concept of an acid anahydride. That's more trivia fact than an explanation to your question, though. :)[/color]

Namiko, the terminology to use here is dependant on which state of matter you are mixing (solid, liquid, or gas).

SOLUTIONS are when you put a SOLID or a GAS into a LIQUID, and the solid or liquid comes apart into individual molecules or ions, and mixes up with the liquid.
(If the solid just stays in clumps, you just have a "suspension" or a "colloid" in the liquid;
if a gas just stays in clumps, then you have "bubbles" ;-)

MIXTURES are when you mix two liquids, two solids, or two gases (ie, substances which were in the same state of matter).
Gases always mix.
Some liquids mix (these are called "miscible").
If you grind solids up into powders, obviously you can then mix those too...

[color=darkgreen]Wait, I don't recall even saying anything about a mixture versus a solution. All I was explaining was the difference between the solvent and the solute and how they add together to form a solution. :?[/color]

um no.....

"but the carbon is still slightly positive, that is, electron defficient, therefore a lewis *acid*"--- That has nothing to do with it. dipole interactions such as the one described have applicability in solvation, spectroscopy, but not in acidity.

CO2 as an empty Pi* orbital that is somewhate low lying and can be used as a LUMO in some circumstances for a lone pair to donate into. This is where it's Lewis acidity comes from.

Re: um no.....

[quote="kman"][quote="alan_chemist"]but the carbon is still slightly positive, that is, electron defficient, therefore a lewis *acid*[/quote]That has nothing to do with it. dipole interactions such as the one described have applicability in solvation, spectroscopy, but not in acidity.

CO2 as an empty Pi* orbital that is somewhate low lying and can be used as a LUMO in some circumstances for a lone pair to donate into. This is where it's Lewis acidity comes from.[/quote]
For a student who has no idea about molecular orbitals (which I assume is the case, apologies if they do), my explanation is clear enough. The MO for CO[size=8]2[/size]:
[img]http://img89.imageshack.us/img89/8707/pagesfromchapter20small2fp.jpg[/img]
As you can see, all of the bonding (and non-bonding) MOs are situated at an energy level close to that of Oxygen's AOs; they can therefore be said to be carrying most of the charge, that is, be δ-.

The empty MOs, antibonding in nature, are located near the empty 2p orbitals of carbon. The 2p orbitals that would usually be carrying 2 electrons. Carbon is, therfore, electron deficient. It is δ+. It is a lewis Acid.

I learned MOs in my first year here, although we were not required to know anything on them beyond simple diatomics until the second year. I know that, when you've never heard of an MO, it is a very strange and confusing concept. Therefore I don't answer questions using them, unless I know that the person asking the question fully understands them.

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