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Originally Posted by phatch  You've got osmosis wrong. Water moves from low concentration to high concentration in the case of salt water and other osmosis situations. This works to equalize the salt concentration by diluting the high concentration while concentrating the plain waters salt.
Hot and cold water wouldn't osmose. There is no osmotic pressure in that case, rather convexion and conduction equalize temperatures.
It's the water that moves, not the salt. Same for other osmosis systems.
Phil |
While its been a while since I got my BP (Bachelor of Physics) I think that there are some errors in both explanations.
One, salt is an ionic molecule only when it is not in solution. Once in solution, it "ionizes" into 1 Na+ plus 1 Cl- and is no longer a "molecule". Since a water molecule is considered "bipolar" the two H+ are about 120 degrees apart, and therefore cause the Oxygen atom to appear as the "--" pole of the bipolar water molecue (as the Oxygen atom has 2 extra electron positions in its outer shell). The Na+ ions are attracted to the double negative side (the oxygen side) of a water molecule, while the Cl- ions are attracted to the + side (two hydrogens) side of the water molecule.
Two, if it were true that "only the water moves, not the salt", then assuming you have a closed system divided in half by the semi-permeable membrane, then eventually one side would contain "nothing" because all the water migrated to the salty side (or conversely, all the water would migrate to the water side, and eventually only dry salt molecules would be left on one side of the semi-permeable membrane). This can't possibly happen because of entropy. Entropy is the desire of all "things arranged in order" to "disorganize". (this same principle explains why old buildings crumble, the universe is not static, and time moves in only one direction).
Luc H's example showed an "ordered" situation where the salty water was "organized" on one side of a permeable membrane and "non-salty" water on the other side. Yes, the ion's of salt, which are attached through ionic attraction to the bi-polar nature of a water molecule would move through the semi-permeable membrane along with the water molecule to which they have become attached. Due to pressure concerns, an "unsalty" water molecule would be forced to move in the opposite direction to attempt to maintain equilibrium.
Given enough time, both volumes on either side of the semi-permeable membrane would be equal in ionized salt content. (This, of course, assumes that the salt content is not "over saturated" such that salt molecules exist in such great numbers that they "clog" the membrane).
Also, on another note, the hot water/cold water isn't quite accurate either. yes convection/conduction play a role, but simply by being "hot"water, the hot water molecules have a higher energy state, and are bouncing around much more actively than the cold water molecules. That higher energy will force some of the hot water through the semi-permeable membrane in order to equalize pressure. That is the same principle that makes a closed system eventually explode as it is heated, unless there is a way to remove the pressure.
Anyway, back to plastic containers. Many plastics, especiallly polyvinylchloride (PVC) contain plasticizers known as Phthalates. These phthalates are securely entrenched in the food chain. They're everywhere, and we got lots of 'em in our bodies right now.
doc