How does polarity affect whether or not one solution or substance will dissolve into another?

Question

2. What are the properties of water that make it a unique substance? Explain why water has these properties.


Thank You For Your Answers!!!

Answer 1

Polar substances like water and ionic solids have an affinity for each other. Non-polar substances like oils and greases have an affinity for each other. Polar and Non-polar do not readily mix.

Answer 2

The general rule for solubility is "like dissolves like"; that is, polar compounds generally have a much higher solubility in polar solvents than non-polar compounds, and non-polar compounds have a much higher solubility in non-polar solvents than polar compounds (which explains why you get layers in a solution of oil and water).

In the case of polar molecules:
Polar molecules are dissolved much more efficiently in polar solvents because polar compounds, by definition, have a dipole, meaning one end is positive, and one end is negative. The solvent also has this quality, so the positive end of the solvent molecule and the negative end of the solute molecule form a weak intermolecular bond, and the negative end of the solvent molecule forms a weak intermolecular bond with the positive end of another solute molecule. This disrupts intramolecular bonds (inTRA meaning inside the molecule, inTER meaning between adjacent molecules), causing a shift in electron density by induction, and also pulls on the molecule, straining the bonds further. So, basically, the intramolecular bonds are pulled apart, and the compound is dissolved into its component ions.

For non-polar, the mechanism is actually quite similar; non-polar molecules form extremely weak intermolecular bonds called London (or Dispersion, or Van der Waals) forces, which basically do the same thing. These forces are somewhat different, because they aren't the result of "formal" semi-charges, but of purely induced dipoles. That is, approaching molecules basically cause opposing charges by a shift in electron density due to differences in electronegativity (or the presence of another more charged molecule, etc). So you end up with tons of these really weak bonds between molecules, and then the solutes is dissolved in basically the same way as in polar molecules.

Polar doesn't dissolve in non-polar (and vice versa), because the solute molecules don't form the requisite intermolecular bonds with the solvent, so the molecules remain intact. As an example, think of a long, saturated hydrocarbon chain (such as octane). Water molecules can't dissolve it very well, because they're so polar, and the hydrocarbon chain is uniformly uncharged. The effect is more pronounced in bigger molecules (ie, longer chains; some oils are dozens or of carbons long), but you get the idea.

Some non-polar molecules dissolve slightly if they have slightly polar parts. Acetone, for example, has a short carbon chain with a double bonded oxygen in the middle. Oxygen is highly electronegative, so it takes a slight negative charge, causing a slight positive on the carbon. However, this carbon isn't very accessible to other molecules (because there are other atoms in the way, which is called "sterics"; solvation at the positive pole is said to be "sterically hindered", meaning basically it doesn't happen often). It gets a bit technical as you get to bigger molecules, but basically just remember this: like dissolves like, and unlike will dissolve much less.

As for water, it isn't exactly unique (as H2S, for example, has very similar properties in terms of polarity), however it is basically just a really good example of a polar solvent. It has a strong partial negative charge, as oxygen is very electronegative, and has 2 lone pairs, and 2 corresponding strong partial positive charges on the hydrogen atoms. It's also a small molecule, meaning it is much less affected by problems associated with sterics than, say, a large or bulky alcohol (such as phenol or t-butyl alcohol, for example).

Because its positive charge is on a hydrogen, it also uses hydrogen bonds, which are basically just a form of polar intermolecules, but with the positively charged hydrogen forming a "hydrogen bond" with a partially negative molecule (particularly via lone pairs, such as with water, or ammonia).


That was far more technical than it had to be... sorry about that, haha.

Answer 3

if you are trying to see if two substances will dissolve in one another you have to look at the polarity. two polar substances will dissolve in one another, as will two nonpolar substances. However, a nonpolar substance (think butter) will not dissolve in a polar substance (think water). "like dissolves like"

Answer 4

the hot compound differences the polarity's dipole moments and so forth discern every time you alter something in chemistry each and every thing reacts to it in in some way and commonly you regularly have a clean subject