Naked Science Forum
Non Life Sciences => Chemistry => Topic started by: neilep on 20/09/2004 21:46:22
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Hello glorious bags of mostly water with Academic IQs d=far advanced than mine ...
I've often wondered what this stuff called ' Heavy Water' is (please forgive moi if my nomenclature is incorrect)....I know it has something to do with Nuclear reactors and stuff from seeing documentaries showing big pools of the stuff etc...so, could you swim in it ?...does it make good ice ?...does it feel and taste like regular good old H2O ?...presumably it's not safe to m x with vodka and stuff eh ?
Your answers of an academically diluted nature would be welcomely received.
ta
'Men are the same as women...just inside out !' (https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.world-of-smilies.de%2Fhtml%2Fimages%2Fsmilies%2FSchilder2%2Finsanes.gif&hash=4f18432872d0188852a6f4a3170ec758)
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Heavy water is is the substance deuterium oxide, or D2O. Deuterium is a stable isotope of hydrogen, the nucleus of which contains a proton and a neutron. (normal hydrogen contains only a proton) Thus, one molecule of D2O weighs 2 more atomic mass units than H2O, hence the name heavy water. While not extraordinarily toxic at low levels (it occurs about one in every 7000 hydrogen atoms), concentrated heavy water can displace normal water in an organism and screw up biochemical reaction rates.
Tritium is another isotope of hydrogen and is unstable, meaning it is subject to radioactive decay, though it is low energy and has a long half life.
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Thanks Jason. I appreciate your explaining it to me.
'Men are the same as women...just inside out !' (https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.world-of-smilies.de%2Fhtml%2Fimages%2Fsmilies%2FSchilder2%2Finsanes.gif&hash=4f18432872d0188852a6f4a3170ec758)
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But to answer Neil's original question - Deuterium is otherwise analogous to water and will make ice. Because it weighs more it will be denser than 'normal' water and hence will produce a greater upthrust for the same displacement. Hence a boat should float higher in a sea of deuterium than it would in a sea of normal water.
Chris
Ylide, feel free to shoot me down if I'm wrong !
"I never forget a face, but in your case I'll make an exception"
- Groucho Marx
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quote:
Originally posted by Ylide
...While not extraordinarily toxic at low levels (it occurs about one in every 7000 hydrogen atoms), concentrated heavy water can displace normal water in an organism and screw up biochemical reaction rates...
Q: Why would heavy water "screw up biochemical reaction rates", since it is electronically identical to light water?
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As a heavier molecule, perhaps the kinetics are different ?
Chris
"I never forget a face, but in your case I'll make an exception"
- Groucho Marx
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I asked first! Do you have a reference for that? I am now intrigued, since isotopes of organic elements are common, such as carbon-12 and carbon-14.
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As Chris said, the kinetics are entirely different. Many biochemical reactions involve hydrolysis and hydrogen ions that interact with the intermediate forms. A deuterium ion weighs about twice what a hydrogen ion does, so any rate determining step that involves a hydrogen ion and it is replaced with a deuterium ion would produce a slower overall rate of reaction. In living systems, changing rates of reaction of biochemical processes can affect the overall status of the organism quite badly.
Now, on a small scale, isotopes aren't a big deal. You have a certain amount of deuterium running around your body under normal conditions. (And carbon-13, carbon-14, nitrogen-15, and hundreds of other isotopes) Note that I originally said concentrated heavy water...i.e. drinking a large quantity of pure D2O. This would displace a sufficient amount of regular water (rather than 1 in 14000 or so molecules that is natural) that it would affect overall biochemical reactions in your body.
D2O is indeed more dense than regular water. H20 has a density of 1.0 g/cc at room temperature and D2O has a density of about 1.1 g/cc, about 10% more dense. This exactly linear with the molar mass of 20 g/mol instead of 18, which is an 11% increase, due to differences in lengths hydrogen, er, deuterium bonds between D2O molecules.
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Hence a boat should float higher in a sea of deuterium than it would in a sea of normal water.
Can that boat still travel, though? I imagine it would be like stuck in the mud for land vehicle.
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The differences between D2O and H2O are pretty subtle. The density of pure D2O is about halfway between that of pure H2O and that of the water in the Dead Sea. And, last I checked, boats work in the Dead Sea (https://igoogledisrael.com/saving-the-dead-sea/)
In addition to being slightly denser than normal water, heavy water has a higher melting point and higher boiling point, higher viscosity, lower surface tension, and higher heat of formation.
https://en.wikipedia.org/wiki/Heavy_water
As correctly pointed out by ylide (a long time ago), one of the primary differences is that chemical reactions in which the rate determining step involves the motion of H atoms or ions will be slower if instead is it D atoms or ions that must move. Also, the nuclear properties are quite different. H nuclei have a spin of 1/2, while D nuclei have a spin of 1 (influencing NMR or MRI signals). H atoms will readily capture neutrons, while D atoms are less likely to do so (which is why heavy water is used in nuclear reactors).
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Suggestions are that:
- Replacing 25% of your bodily water by D2O causes sterility
- Replacing 50% of your bodily water by D2O causes death in a week
See: https://en.wikipedia.org/wiki/Heavy_water#Effect_on_animals
As for swimming in a nuclear reactor pool:
- Swimming in pure, fresh D2O is fine, and quite buoyant, provided you don't drink too much of it (like liters)
- Cooling water in power reactors is pressurised and very hot (well above 300C): Avoid these!
- Unpressurised and low-temperature pools in research reactors wouldn't kill you directly, unless you dived down, and the neutron radiation from the nuclear core poisoned you
- D2O that has been used in a nuclear reactor becomes contaminated with Tritium, which is radioactive. It decays by emitting a fairly low-energy electron (18.6 keV), so you are fine as long as you don't swallow any, and have a shower afterwards...
But seriously, don't try this at home!
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so you are fine as long as you don't swallow any, and have a shower afterwards...
Also, remember not to breathe.
Not that it will help much. Water soaks into the skin.
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This is the Deep Purple of water. "Smoke on the water .... a 🔥 in the sky". Heavy man!
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so you are fine as long as you don't swallow any, and have a shower afterwards...
Also, remember not to breathe.
Not that it will help much. Water soaks into the skin.
Should I also close my eyes?