OT: Liquid water is composed of 150-unit branching polymers

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chains, where the hydrogen bonds that hold the individual water molecules t ogether last for about 90.3 femtoseconds, makes every kind of sense, and do es explain why water is as odd as it is.

Which water weirdness will this work over?

Rick C.

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There are so many; the slipperyness of ice, the expansion on solidification, the unusual sensitivity to contamination in 'polywater', the combination of polar and nonpolar solubilities, and there's another frontier entirely in the behavior of concentrated solutions (important in electroplating).

Water isn't an easy experimental subject, because there's a LOT happening. A theory with a lot happening, ought not surprise anyone.

Universal solvent. Snow.

George H.

It's an ionic solvent, far from universal. What's unusual about snow? Crystals of water. The only thing about snow that is unusual is that it condenses from our atmosphere, no?

Rick C.

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Expanding on crystallization is because as water the molecules fit together in an dense manner but on solidification they rearrange to a lattice with a fixed spacing. The slipperiness is because of this, applying pressure me lts the ice forming a thin layer of water which is a lubricant.

Perhaps I have forgotten my chemistry, but I thought water was not a good s olvent for non-polar materials. Ever hear of mixing like oil and water?

Rick C.

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This insane golden chamber contains water so pure it can dissolve metal...

Terrifyingly pure water

"Pure water is very, very nasty stuff. It has the features of an acid and an alkaline."

"Apparently somebody had left a wrench there when they filled it in

Twaddle. Pure water is neutral - it contains equal numbers of H3O+ and OH- ions, at about 100 molecules per billion molecules of regular H2O.

If there was oxygen in the water (which seems likely) a wrench could rust and corrode away, probably more slowly than it would in less pure water, but just as inevitably.

That's one theory; another is that ice surface has excess hydroxyl ions, forming a liquid film, and the hydroxyl-film also explains frost heave and ice self-fusing.

"Polywater" ? Do you want to include "water memory" and "pentawater" in your list?

There are enough unusual and interesting properties of water without bringing pseudoscience into it.

I think the many types of ice (18 known forms) are an interesting aspect of water. Other substances have more than one solid form, but water has lots. Part of that, of course, could simply be that water has been studied more than most substances.

That certainly seems to be part of the effect. But it does not apply to gallium, which also expands on freezing - when it is solid, it is not slippery under reasonable pressure. (It is, of course, slippery when there is melted gallium on the surface.)

The "pressure causes melting" idea does not explain why ice is slippery even with low pressure, nor does it fully explain ice skating. The slipperiness of ice is a combination of several effects.

It can dissolve and mix with many non-polar materials - sugar being a rather important one for biology. Of course it does not dissolve all non-polar materials - but it handles more than most polar liquids, and can support an extraordinarily wide range and quantity of dissolved substances.

Not many other molecules are the shape of water (boomerang-shaped), and the ones that are, are nowhere near so polarized.

Regarding solid forms, consider the hypothetical situation where you have to make a tidy fire-wood stack from a large pile of 3" thick logs, all 18" long, and all bent 30 degrees in the middle. I bet you could have a fun time finding the endless different ways of making a stable stack.

Thank Bokonon we haven't let any ice-9 fall into the ocean!

Clifford Heath.

Terrifyingly pure water

Pure water has a theoretical pH 7 but tends to be around pH 4 if it is open to the air which is a pretty weak acid but an acid none-the-less. Its pH when truly pure is pretty much undefined unless you buffer it.

Ultra pure water is quite corrosive. Much more so than tap water. You have to be quite careful about the design of stuff that will be used to handle it. Mistakes made in the design of such kit are expensive.

I'd be a bit surprised if it dissolved a wrench with no residue in five years but I have seen people have problems through assuming that DI water is a benign environment for engineering materials like tap water.

In real cooling systems using DI water various organic additives are added to passivate the metal surfaces. Otherwise the pure water keeps on ripping metal ions off the surface and dumping them into the ion exchange column used to keep the water pure. I recall one where they got it badly wrong and seaweed like green nickel gels gummed up the works. It looked like something off alien when we opened it up.

Pure water has a pH of 7. Absorption of other things - such as CO? from the atmosphere - change its pH. Pure water can act as either an acid or a base, depending on what it interacts with.

That contains the usual nonsense about pure water - "DI water is one of the most aggressive solvents known." Yeah, sure.

Purified water (however it is done, and to whatever levels) is a slightly better solvent than tap water simply because it contains less dissolved minerals and impurities. The ability of a given quantity of water to dissolve, say, salt decreases with the concentration of salt in the water. The maximum solubility occurs when the water currently has no salt (and little of anything else). But it is not particularly corrosive - just slightly more than "ordinary" water. And of course once the pure water has corroded something and absorbed some of the ions, it is no longer pure!

There are lots of myths about how dangerous pure water is supposed to be. People will tell you that drinking a glass will kill you, or it can strip the skin from your hand. (Other people will tell you of great health benefits from drinking their expensive bottled deionised water.)

Deionised water is as benign as tap water with regard to corrosion - certainly vastly more benign than heavily ionised water (like sea water). If you are talking about materials that slowly dissolve in water, such as copper pipes, then they will do so marginally faster with a steady flow of deionised water than tap water - but only marginally so.

They don't use deionised water to stop the corrosion - they use it to avoid laying down minerals! Normal ionised water gradually leaves scale in many systems, which is the main reason to want to avoid it. (Other reasons include avoiding conductivity, and because you don't want pollutants in your semiconductors, pharmaceuticals, etc.)

True enough in theory but in real world practice it generally has oxygen and carbon dioxide dissolved in it. That is enough for it to be quite aggressive against materials that ordinary tap water would be fine in.

It is a very powerful *solvent* and will take ions off the surface of almost anything including lab glassware if you have the equipment to measure it. I worked on the software for ultratrace analytical equipment destined for the semiconductor industry and capable of sub-ppq detection limits for key nuisance elements in suitably pure "raw" materials when prepared under clean room conditions. The length of time a sample could sit in a test tube before being analysed was carefully controlled.

Pure water is a theoretical abstraction which almost never occurs in real life. The process equipment has to handle the real material perhaps under a nitrogen blanket and with sub boiling point distillation for the very best grades of semiconductor pure reagents.

I agree there are a lot of myths about. It is rather keen on becoming impure. No more and no less. It tends to find any weak spots - stresses around welded joints and that sort of thing.

No it isn't. The tap water tends to have enough calcium and magnesium in it to form a thin barrier layer on the pipes. No such protection is afforded to pipes with distilled or DI water inside.

We were at one time using it to cool a component at 8kV above ground. I reiterate my point for the hard of hearing - engineers fall foul of the belief that DI water is harmless to metals with monotonous regularity.

Hardly long enough to count up to 150...

Mike.

Polywater was "real" science for a while. There's a book:

No, it is not. First, in places where very pure water is used, it is kept carefully - precisely so that it does not get contaminated by other things. Secondly, if it is exposed to air it does not get more oxygen or carbon dioxide than you would normally have, and it is /not/ noticeably more "aggressive" than tap water.

When you boil the kettle in your kitchen, the water vapour condenses around the room. As it condenses, it is very pure deionised water. Do you worry about it corroding your kitchen appliances? Do you worry about it dissolving the paint of the walls? Of course not. It is /water/, nothing more. It does not turn into some super-acid just because it doesn't have the few milligrams of salts that you find in tap water!

The challenge with pure water is not that it attacks things and destroys them - it is that it very quickly becomes non-pure water by dissolving tiny, trace amounts of ions from many surfaces. You don't worry that you've paid for your expensive pipe and the pure water is ruining it - you worry that you've paid for your expensive pure water, and the pipe is ruining it.

/Water/ is a powerful solvent. Pure water is slightly better, but not so that you'd be concerned.

Pure water doesn't take any more ions off the surface of materials than tap water. If a litre of water strips a milligram of iron ions off a surface, no one cares about the surface. For tap water, no one cares about that milligram - it adds to the 100 mg or more already dissolved there. But for pure water, that 1 mg stops it being pure any more.

The problem is that the pure water stops being "pure" once it has traces of dissolved or suspended particles.

That is all so that your pure water stays pure.

Exactly.

Sure - but it doesn't harm them noticeably more than ordinary water would.

It is a minor thing, and it is not hard to avoid such problems - it is often harder to deal with too much deposited minerals from tap water. But it /is/ hard to ensure that the pure water stays pure.

Far more often, people believe deionised water has some sort of magical properties turning it into the most vicious substance known to man.

Is this your usual high-quality "science" knowledge?

is around 18 megohms/cm:

Any active metal above ground will undergo electrolysis. This will add ions into the water and increase the conductivity, which increases the current.

Some conductors do not exhibit this phenomenon. Gold, titanium, platimum, carbon are examples.

There are various limits to the increase. For example, silver tends to self-limit at around 20 ppm due to the formation of silver hydroxide. Copper has a much lower limit, around 3 ppm. The reason is copper tends to make tendrils from the anode to the cathode that short out the conductivity.

Originally, buried telephone wires quickly degraded due to electrolysis. The solution was to put them at a negative voltage with respect to ground, around -48V. This stopped the corrosion.

Many houses use dielectric barriers in the water pipes to reduce corrosion. These are non-conductive separations in the water pipe at the entrance to the building to stop the electrolysis from happening.

Whenever you have different metals in contact with moisture, you can have corrosion. The US Navy has had serious problems with ships where aluminum and steel are in contact. They never seem to realize this is a problem.

You can see the difficulty by examining the Galvanic Table. There are many examples, such as

The absorption of Carbon Dioxide is rarely a problem. First, distillation drives out all the absorbed gasses. Second, the concentration of CO2 is very low. Third, the production of carbonic acid is a small percentage of the amount of CO2 that is absorbed: