Hello scientific community,
I have doubts regarding the self diffusion coefficient of heavy water in H2O.
I am trying to understand how the different isotopes of H and O may affect the diffusion of the heavy water molecules in H2O. In particular:
- how do D2O, H2-18O and DHO diffuse in H2O?
- is the diffusion facilitated for the heavy molecules with respect of the lightest if these latter represents most of the water mass?
Please forgive the dumb questions, this field of study is far from mine.
Many thanks in advance!
In my opinion heavy water molecules D2O diffuse with very low speed between H2O molecules. To simulate this have the diffusion of water in ethanol, this can be similar. Use a teaspoon of water and some wiskey. :)
Hello Alessandro Montemagno ,
Please see my RG page: Method Self-Diffusion in Water Derivation
The description at the top of the page cites two papers on the experimental work by Wang in 1951 on this subject, and my derivation of Wang's mathematics is at the bottom of the page.Regards,
Thomas Cuff
Hello Alessandro Montemagno ,
I finally located my copies of Wang's two articles, and it is interesting to read them as he voices the same concerns as you in your question. In order to measure the diffusion coefficient, D, he has to use a tracer that is similar to water but slightly different. Note, by the term 'tracer' he does not mean a radioactive tracer just something with slightly different physical characteristics from water, H20. Initially, he utilized D2O, deuterium oxide. But, like you, he had questions about how D2O associated with normal water by hydrogen bonding. So, in his second paper, he tried water with a different isotope of oxygen, H2O18. He also tried DH2O. I think you will find his thinking quite similar to yours in the way he questions his assumptions and tries to answer these objections with different tracers. I hope this helps.
Regards,
Thomas Cuff
Dear Doctors Bogatu and Cuff,
many thanks for your answers, I will surely give a look at the publications cited!
Best regards,
Alessandro
Dear Alessandro Montemagno In addition to all previous interesting answers to your thread; Yes, there are differences from the molecular physical point of view in the diffusion coefficient in liquids & gases, including self-diffusion (even they both are part of the fluid dynamics field of study).
I elaborate briefly as in a molecular physics second-year course following a Russian instructive blog * which has some references at the end:
- In liquids, the diffusion coefficient is several orders of magnitude lower than in gases at atmospheric pressure: in non-viscous liquids, at 20°C it is on the order of 10–9 m2/s, and in gases, it is (1–10) 10–5 m2/s.
- However, it does not follow from this that the flux density in liquids is less than in gases since the density of liquids and concentration gradients in them are usually higher.
- In liquids, the diffusion coefficient depends significantly on the concentration of the distributed substances as you point out. This is due to the denser packing of molecules and, as a result, stronger molecular interaction among different subcomponents.
Please translate using google the following Russian link:
*http://chemanalytica.com/book/novyy_spravochnik_khimika_i_tekhnologa/08_elektrodnye_protsessy_khimicheskaya_kinetika_i_diffuziya_kolloidnaya_khimiya/5017
Best Regards.
Dear Dr. Pedro L. Contreras E. ,
many thanks for these additional (and welcome) insights.
I will surely make use of them.
Best Regards,
You are most welcome, Dear Alessandro Montemagno
During the former USSR times, we studied a 2nd-year course in molecular physics and all those questions were taught at the elementary level. They consider diffusion as part of statistical physics course from the beginning, in western countries diffusion is considered a part of the 2nd theoretical physicochemical course, only a last chapter, in the statistical physics course sometimes.
Try with google translator from Russian to English/Spanish, it worked for me, even I read Russian.
Best Regards.
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