Has there been an improved understanding of water ?
- Thread starter river
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exchemist
Valued Senior Member
Er....I had thought water was fairly well understood by now. Are you thinking of anything in particular?
Yes
How both hydrogen and oxygen become liquid at room temps.
When both ONLY become liquid , separately , at extreme cold temps
-256 and -236 respectively
Water is the most researched material in all of science.
What makes water so special, is water exhibits 69 known anomalous properties. These are properties that differ from the trends of other solids and liquids. For example, water will expand when it freezes. This is very odd and is only found in one other natural material.
One cool anomaly, that had an impact on modern navies, is the speed of sound in liquid water reaches at maximum at a certain pressure. This will cause sonar to bounce off the water at a certain depth and reflect back rather than go any deeper. The subs can hide under this invisible floor.
Research has also been done with water at extreme temperature and pressure. Water becomes a metallic solid at the temperature and pressure that are assumed in the iron core of the earth. Metallic water is more than likely mixed with the iron.
Water is also important to life, with some of the anomalies, unique to water, useful to life.
What makes water so special, is water exhibits 69 known anomalous properties. These are properties that differ from the trends of other solids and liquids. For example, water will expand when it freezes. This is very odd and is only found in one other natural material.
One cool anomaly, that had an impact on modern navies, is the speed of sound in liquid water reaches at maximum at a certain pressure. This will cause sonar to bounce off the water at a certain depth and reflect back rather than go any deeper. The subs can hide under this invisible floor.
Research has also been done with water at extreme temperature and pressure. Water becomes a metallic solid at the temperature and pressure that are assumed in the iron core of the earth. Metallic water is more than likely mixed with the iron.
Water is also important to life, with some of the anomalies, unique to water, useful to life.
But why does the molecule of H2O become liquid at room temps. ? Has anybody figured out the why ?
What ever happen to that high density water that Deriagen come up in the 1970 were he pushed eater through some capillary ?
KitemanSA
Registered Senior Member
Water becomes liquid at a higher temperature because it is a polar three atom molecule.
KitemanSA
Registered Senior Member
Well, not quite. The acoustic barrier is due to salinity and temperature gradients, not pressure.
KitemanSA
Registered Senior Member
Turned out it was dirty water. It absorbed some of the material the tube was made out of and got thicker (more viscous). I THINK it was a glass tube and the water absorbed some of the silicon dioxide.
KitemanSA
Registered Senior Member
Actually, you have your question backwards. The real question is why is room temperature what it is? Answer, cuz that is where liquid water allows complex life to be comfortable.
exchemist
Valued Senior Member
Sure. This is just one of the many effects of hydrogen bonding. You are right that your average triatomic molecule with a MW of 18 would be expected to be a gas at NTP. After all, CO₂ is a gas and is a triatomic molecule with a MW of 44. But "your average" molecule only experiences Van der Waals attraction between one molecule and the next. A molecule capable of hydrogen bonding, on the other hand, experiences far stronger binding forces between the molecules.
This Wiki article has quite a lot about it: http://en.wikipedia.org/wiki/Hydrogen_bond
If your question was a hidden way of asking whether people understand hydrogen bonding properly, I would have said that's a fair question. When I was at university in the early 70s, I don't think it was really settled. I see the Wiki article says the consensus now is that it is a dipolar, i.e. electrostatic, bond, rather than a covalent one. But I'd need to read up on this before commenting further.
exchemist
Valued Senior Member
Haha, yes, I did a bit of work on that when I was at school, in 1971. It was called "anomalous water" and was thought by its discoverers to be a polymer of water. It was made in fine silica capillaries and I had a lot of fun heating silica tubes and pulling them out into long threads. I even made some of this funny water: at least we had some inside some capillaries that did not freeze until about -40C or so.
But it turned out to be all due to surface effects and/or contamination in the tubes: http://www.britannica.com/EBchecked/topic/26575/anomalous-water
KitemanSA
Registered Senior Member
I think this is a fancy way to say that water is a polar molecule and the electro-static forces hold them together better (liquid at a higher temperature) than non-polar molecules like CO2 or CH4.
exchemist
Valued Senior Member
Well, could be, I suppose. However my recollection is that it takes more than the relative sizes of dipole moments to account for the strength of hydrogen bonds, compared to other kinds of dipoles in molecules.
I seem to recall ideas that the lone pairs of electrons on oxygen were thought to participate in some way with the hydrogen of an adjacent molecule. Since oxygen has 2 lone pairs and 2 hydrogens, water would then have the most efficient ratio of any simple molecule to form H bonds. But...this is old, half-remembered chemistry and may have ben overtaken by more modern theories. Do you have a good source of up to date thinking about H bonding that you can refer me to? I'd be interested in updating myself.
High density water?
Do you mean heavy water?
exchemist
Valued Senior Member
Kiteman, further to my previous reply, I've done a bit of reading on the internet. It seems I was right: the lone pairs on the electronegative atom ARE involved i.e. there is a directional charge distribution of the nominally non-bonding electrons in the valence shell, and there IS evidence for some covalent character to the H-bond.
So it is not fair to say the H-bond is just a fancy term for attraction between dipoles. It really is a special class of chemical bonding, with a strength intermediate between that of Van der Waals forces on the one hand, and of either normal 2-centre covalent bonds or ionic bonds involving full charge separation, on the other.
The hydrogen bonding within water is both van der Waals (polar) and covalent. When water expands when it freezes, this is due to the bonding orbitals of hydrogen and oxygen needing to spread out for proper overlap; covalent bonding. Van der Waals is more about polar attraction, which should get closer as the energy lowers within freezing, which is the case of almost all materials. But water, but using covalent hydrogen bonding, will expand for proper bonding orbital overlap.
In liquid water, the average H2O molecule only lasts about 1 milli-second before it swaps covalently bonded hydrogen. Water is always new molecules. There is no ancient H2O but all are hot off the press. The covalent aspect of the hydrogen bonding, acts like an intermediate covalent state, allowing covalent bond breaking and hydrogen hopping at ambient conditions; pH.
Say we add pressure. Pressure wants to squish water molecules closer together. But when water freezes it wants to expand. The result is the pressure will lower the freezing point, since it inhibits the needed expansion.
If you ever heard the term surface tension, tension implies stretching which, in water, is connected to the expanded covalent state. If we mixed water with oil, the oil interrupts water hydrogen bonding with itself. The higher induced energy within water needs to lower with the covalent state of hydrogen bonding being slightly lower in energy. This surface tension is the lowest energy compromise. But because this is under tension compared to the van der Waals average in water, it is full of potential energy. Life uses this energy.
In liquid water, the average H2O molecule only lasts about 1 milli-second before it swaps covalently bonded hydrogen. Water is always new molecules. There is no ancient H2O but all are hot off the press. The covalent aspect of the hydrogen bonding, acts like an intermediate covalent state, allowing covalent bond breaking and hydrogen hopping at ambient conditions; pH.
Say we add pressure. Pressure wants to squish water molecules closer together. But when water freezes it wants to expand. The result is the pressure will lower the freezing point, since it inhibits the needed expansion.
If you ever heard the term surface tension, tension implies stretching which, in water, is connected to the expanded covalent state. If we mixed water with oil, the oil interrupts water hydrogen bonding with itself. The higher induced energy within water needs to lower with the covalent state of hydrogen bonding being slightly lower in energy. This surface tension is the lowest energy compromise. But because this is under tension compared to the van der Waals average in water, it is full of potential energy. Life uses this energy.