Heavy Water - Physical Properties (with Comparison To Light Water)

Physical Properties (with Comparison To Light Water)

Property D2O (Heavy water) HDO (Semiheavy water) H2O (Light water)
Freezing point (°C) 3.82 0.0
Boiling point (°C) 101.4 100.7 100.0
Density at STP (g/mL) 1.1056 1.054 0.9982
Temp. of maximum density (°C) 11.6 4.0
Dynamic viscosity (at 20 °C, mPa·s) 1.2467 1.1248 1.0016
Surface tension (at 25 °C, μJ) 7.187 7.193 7.198
Heat of fusion (cal/mol) 1,515 1,436
Heat of vaporisation (cal/mol) 10,864 10,757 10,515
pH (at 25 °C) 7.43 (sometimes "pD") 7.266 (sometimes "pHD") 6.9996
Refractive index (at 20 °C, 0.5893 μm) 1.32844 1.33335

Physical properties obvious by inspection: Heavy water is 10.6% denser than ordinary water, a difference which is not immediately obvious. One of the few ways to demonstrate heavy water's physically different properties without equipment is to freeze a sample and drop it into normal water (it will sink). If the water is ice-cold the higher melting temperature of heavy ice can also be observed – it melts at 3.8 °C, and thus holds up very well in ice-cold normal water.

An early experiment reported not the "slightest difference" in taste between ordinary and heavy water; on the other hand, rats given a choice between distilled normal water and heavy water were able to avoid the heavy water based on smell, and it may be possible that it has a different taste.

No physical properties are listed for "pure" semi-heavy water, because it is unstable as a bulk liquid. In the liquid state, a few water molecules are always in an ionised state, which means the hydrogen atoms can exchange among different oxygen atoms. Semi-heavy water can be created by a chemical method but would rapidly transform into a dynamic mixture of 25% light water, 25% heavy water, and 50% semi-heavy water (however if it were made in the gas phase and directly frozen to a solid, this semiheavy ice would be stable).

Read more about this topic:  Heavy Water

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