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Author Topic: what is 'heavy water' - can you swim in it ?  (Read 11761 times)

Offline neilep

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what is 'heavy water' - can you swim in it ?
« on: 20/09/2004 21:46:22 »
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

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Offline Ylide

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Re: what is 'heavy water' - can you swim in it ?
« Reply #1 on: 21/09/2004 09:08:57 »
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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Offline neilep

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Re: what is 'heavy water' - can you swim in it ?
« Reply #2 on: 21/09/2004 09:20:13 »
Thanks Jason. I appreciate your explaining it to me.

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Offline chris

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Re: what is 'heavy water' - can you swim in it ?
« Reply #3 on: 21/09/2004 11:04:06 »
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

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Offline gsmollin

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Re: what is 'heavy water' - can you swim in it ?
« Reply #4 on: 21/09/2004 14:55:49 »
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?

 

Offline chris

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Re: what is 'heavy water' - can you swim in it ?
« Reply #5 on: 21/09/2004 15:06:31 »
As a heavier molecule, perhaps the kinetics are different ?

Chris

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Offline gsmollin

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Re: what is 'heavy water' - can you swim in it ?
« Reply #6 on: 22/09/2004 18:13:04 »
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.
 

Offline Ylide

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Re: what is 'heavy water' - can you swim in it ?
« Reply #7 on: 23/09/2004 04:26:03 »
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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Re: what is 'heavy water' - can you swim in it ?
« Reply #7 on: 23/09/2004 04:26:03 »

 

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