The Concept of Heavy Water

In 1931, an American chemist Harold Urey discovered the hydrogen isotope deuterium. Two years later, Newton Lewis came up with the concept of heavy water by electrolytic chemical reaction. Nowadays heavy water is extensively used for research purposes and in nuclear reactors. 

Properties of Heavy water

The nuclear properties of heavy water can be easily distinguished from normal water due to the presence of a heavier isotope, deuterium (2H2). They have a high molar mass of about 20.026 g mol-1. Heavy water readily forms a homogeneous solution with other substances. The boiling point of 101.4°C is slightly higher when compared to water. Also, the density (1.1056 g/mL) and viscosity (1.2467) at Standard Temperature and Pressure (STP) are comparatively higher than in light water. Semi-heavy water is a dynamic unstable liquid mixture of light, semi-heavy and heavy water, therefore its nature is not recorded. 

Heavy water is obtained by spending a large quantity of energy to facilitate the chemical procedure of electrolysis or distillation. More separation is seen among D+ ions in comparison to H+ ions (present in normal water) at a given temperature. The same phenomenon is noticed in the anion counterpart OD-. The ion product constant (kW) of heavy water is equivalent to that of normal water. 

The potential of deuterium in heavy water is calculated with the help of pH electrodes at a varying range of temperatures. The apparent pH reading (pHa) comes almost identical to the pD+ value. 

The density (1.1056 g/mL) of heavy water is 10% more than normal water. It helps the heavy water to remain frozen even if the temperature exceeds the normal melting point of water. 

Heavy water does not absorb red color wavelengths of the visible spectrum due to constant molecular vibration at regular intervals. Thus it lacks the intrinsic blue hue of normal water. 

Heavy Water is obtained by which Method? 

Manufacturing heavy water involves an elaborated process that is marketed as electrolysis. The chemical process is carried out in presence of an alkali, normally caustic soda is used. 

The electrolyte used here is an aqueous solution of caustic soda. Porous nickel plates serve as anodes while a steel vessel acts as the cathode. The heavy water is produced as the end product after a stream of carbon dioxide is made to pass through the electrolytic solution. This resultant water is non-radioactive as it does not have a sufficient amount of tritium atoms. 

Impact of Heavy Water on Nature

Unlike other elements, hydrogen isotopes behave in greater contrast owing to reduced molar mass between tritium, deuterium, and protium.

As water is a universal solvent, the isotopic differences pose larger influences on the overall biological environment. An endogenous circadian rhythm that is driven by the surrounding environment in living organisms is affected by heavy water in unicellular organisms, small birds, rodents, and insects. It prolongs the completion of each internal clock cycle which affects their health. 

Protein-based enzymes that catalyze physiological processes within a living organism readily interact with hydrogen bonds. This is done to improve the stability of recurring tertiary structure domains that compose molecular building units. In deuterium oxide as the strength of hydrogen bonding is greater when compared to normal water, a few regular intercellular processes might get hindered. In eukaryotic plants, cell division completely shuts down when they are supplied with heavy water. The inclusion of heavy water in the atmosphere proves to be harmful to multicellular organisms. 

To initiate fatal reactions the human body must ingest adequate amounts of heavy water for several days. Small oral doses can be prescribed by medical practitioners to treat metabolic disorders. If the prescribed dosage exceeds a certain limit, blood pressure may drop significantly. The usual symptoms are lightheadedness and dizziness. 

Commercial deuterium oxide or heavy water is made up of two deuterium atoms that are not radioactive. It has a very less amount of tritium in comparison to its counterpart i.e., the heavy water which finds use as a cooling agent in nuclear power plants. The radioactive nature of tritium is generated by bombarding neutrons in the nucleus of the deuterium atom. 

Heavy Water – Uses

• Heavier hydrogen atom – deuterium is produced from heavy water. 
• Heavy water is used by researchers to study biological activities in green plants such as photosynthesis. It has been proved that higher amounts of heavy water affect germination and cell division in plants.
• Isotopes of different elements are combined with deuterium oxide molecules to prepare isotopologues. 
• Neutron bombardment is done to add radioactivity in deuterium atoms by converting them into tritium. The tritium finds use in nuclear reactors. 
• To study the magnetic field surrounding the nucleus of an element we incorporate the use of NMR spectroscopy. D2O is used to serve the purpose. 
• Disorders in metabolism are treated in humans using heavy water. 

Conclusion 

Heavy water is produced by electrolysis. It is not fit for consumption and other daily activities as the properties are vastly different from normal water. It is used for research purposes. Heavy water gives rise to a homogeneous solution when combined with normal water.