Heavy water is chemically identical to the ordinary or light water, we know and love. Heavy water makes up a small percentage (0.02%) of water naturally occurring on Earth. Heavy water occurs naturally, although it is much less common than regular water. Approximately one water molecule per twenty million water molecules is of heavy water because only about 0.015% of all naturally-occurring hydrogen is in the form of deuterium.

Definition:


"Heavy water or Deuterium Oxide (D2O), is water in which both hydrogen atoms have been replaced with deuterium, the isotope of hydrogen containing one proton and one neutron and one orbiting electron."

The hydrogen isotope with a mass double that of ordinary hydrogen, and oxygen. Thus, heavy water has a molecular weight of 20 g (the sum of the atomic weight of two deuterium atoms plus the atomic weight of oxygen, which is 4+16=20 g), whereas ordinary water has a molecular weight of about 18 g. It is the extra neutron that makes heavy water "heavy", about 10% heavier infact than ordinary water.
World Oceans, polar and mountain ice and atmospheric moisture are the main natural “factories” of deuterium production. Heavy water is said to be fully Earth born product.


Comparing physical properties of Heavy Water and Light Water

Melting Point (C) of D2O (Heavy Water) is 3.82 C while for H2O (Light Water) 0.00 C.
Boiling Point (C) of D2O (Heavy Water) is 101.4 while for H2O (Light Water) 100.0 C
Density (at 20 C, g/ml) of D2O (Heavy Water) is 1.1056 while for H2O (Light Water) 0.9982
Temp. of maximum density (0C) of D2O (Heavy Water) is 11.6 while for H2O (Light Water) 4.0
Viscosity (at 200C, mPas) of D2O (Heavy Water) is 1.25 while for H2O (Light Water) 1.005
pH (at 25 0C) of D2O (Heavy Water) is 7.41 7.00 while for H2O (Light Water)
Molar mass (g/mol) of D2O (Heavy Water) is 18.0153 while for H2O (Light Water) 20.0275


Applications of Heavy water:

Used as moderator in Nuclear Reactors:

Heavy water (D2O) is one of several commonly used moderators found in nuclear reactors (others include graphite, beryllium etc). A moderator slows down fast-moving neutrons released by nuclear fission so they have more time to react with the nuclear fuel. That permits a sustained, controlled chain reaction using un-enriched uranium.

As a solvent in chemical Laboratories:

Deuterium oxide is used in nuclear magnetic resonance spectroscopy because Deuterium has a different magnetic moment from hydrogen and therefore does not contribute to the NMR signal at the hydrogen resonance frequency when solvent is water. Deuterium oxide is often used instead of water when collecting FTIR spectra of proteins in solution to avoid overlap of amide region arising from H2O.