Sinking ice: a phenomenon linked to the density of heavy water

We all know it: ice it floats on the water. This happens because the density of ice is smaller than liquid water. However, there is a form of ice which, on the contrary, sinks into water: this type of ice is formed from water deuteratedalso called water heavywhich instead has one higher density of normal water. Let’s see what this particular type of ice is made of and why, unlike normal ice, it sinks.

What is heavy water that causes ice to sink

Heavy water is a form of water that contains atoms of deuterium (D or ²H) instead of normal hydrogen (H). The deuterium is an isotope of hydrogen, that is, an atom that has a neutron more than hydrogen. This causes heavy water molecules (D₂O) have one mass greater than normal water (H₂O).

When does ice sink and what does heavy water have to do with it

Now, under normal conditions, the ice normal it floats because it has a lower density than water. Specifically, the density of normal ice is around 0.917 g/cm³while water is approx 1 g/cm³ (the dependence on temperature should also be considered, but the value does not differ much).

From a molecular point of view, the lower density of ice comes from the fact that i ties to bridge hydrogen between H molecules_₂Or they cause water molecules to organize themselves into a structure crystal clear which takes up more space compared to the disordered arrangement of molecules in phase liquid. This then makes normal ice less dense and allows it to float on water.

If instead the water is made up of heavy water or water deuteratedthe situation changes. Heavy water molecules form an ice crystal more “heavy” compared to ice of normal water. In fact, the density of heavy water ice is greater than that of liquid water. We are talking about a density of 1.105 g/cm³. Therefore, contrary to what happens with normal ice, D₂OR sinks.

What is heavy water used for?

In nature, ice is practically heavy Not exists. This is because there is a lot of deuterated water less plentiful compared to normal water and moreover it is always mixed with normal water. So there is no deuterated water pure in nature. It must be said, however, that in controlled environments, such as in scientific laboratories, it is possible to find it. Thanks to particular separation techniques it is possible to obtain a liquid consisting practically only of D₂Or, actually called deuterated water.

Water can then find various practical applications, such as:

1. Solvent for carrying out spectra NMR (resonance magnetic nuclear);
2. Useful in neutron scattering techniques, in particular in small-angle neutron scattering (SANS);
3. Used in research to improve effectiveness and the safety of the drugs.