Heavy Water
What is Heavy Water?
Heavy water or deuterium oxide (chemical formula D2O) is a compound that contains oxygen and deuterium rather than the common hydrogen. The atomic mass of the heavier hydrogen isotope or deuterium (1H2) is higher than that of the normal hydrogen or protium (1H1) isotope. The presence of the heavier hydrogen isotope in water gives slightly different physical, and chemical properties when compared to normal water.
Heavy water has a greater molar mass than regular water since the atomic mass of deuterium is greater than that of normal hydrogen.
Properties
Heavy water has a colourless liquid at room temperature and it forms a homogeneous mixture when mixed with normal water. The density of deuterium oxide is approximately 11% greater than that of normal water. Some properties of heavy water are given below,
- Chemical formula: D2O
- Molecular Mass: 20.02 grams/mole
- Density: 1.107 g/mL
- Dipole moment: 1.87 D
- Melting Point: 3.82 °C
- Boiling Point: 101.4 °C
- Appearance: Colorless liquid soluble in normal water
- CAS Number: 7789–20–0
The chemical properties of deuterium oxide differ from normal water because the isotopes of hydrogen exhibit different chemical behavior, owing to the differences in their atomic masses.
The solvent properties of water change due to the presence of high quantities of deuterium. It may adversely affect biological systems.
At a given temperature, the concentration of deuterium ions in a deuterium oxide sample is generally lower than the concentration of hydrogen ions in a water sample.
Facts about Heavy water
- Protium (H) and deuterium (D) are two isotopes of hydrogen that have 0 and 1 neutrons in their nucleus. Heavy water contains deuterium atoms instead of protium in its molecules.
- Deuterium oxide was first produced in the year 1932, a few months after the discovery of deuterium. Deuterium oxide is used mainly as a neutron moderator and coolant in pressurized heavy water reactors (PHWR).
- Heavy water can be prepared by the prolonged electrolysis of alkaline water and neutralized by the passage of carbon dioxide gas.
- The molecular mass of D2O is not substantially greater than that of H2O because 89% of the molecular mass of a water molecule is attributed to oxygen.
- The density of deuterium oxide is higher than that of normal water and the deuterium-oxygen bond in deuterium oxide is stronger than the protium-oxygen bond in normal water.
- It is not radioactive in nature because the deuterium atom does not show radioactive decay.
- High levels of heavy water may be toxic for many living organisms.
Other heavy forms of water
Other three heavy forms of water are observed along with deuterium oxide. These three heavy forms are semi-heavy water, heavy-oxygen water, and tritiated water.
Semi-heavy water
Semi-heavy water is formed by mixing one protium, one deuterium, and one oxygen atom. It is denoted by the formula HDO.
In a water sample, hydrogen atoms exchange with each other, and exists a dynamic equilibrium between HDO, D2O, and H2O. A water sample containing an equal ratio of protium and deuterium forms 50% semi-heavy water, 25% normal water, and 25% heavy water.
Heavy-oxygen water
Water containing heavier isotopes of oxygen such as 17O and 18O than normal oxygen is called heavy-oxygen water. It is used in the production of the fluorine-18 isotope. It is also used in the radiotracers and radiopharmaceuticals industry.
Tritiated water
Tritiated water is a radioactive form of water that contains tritium instead of a protium atom. It is commonly called super-heavy water and is denoted by the chemical formula T2O. Tritiated water may be used for the determination of the total volume of water in a body.
Uses of heavy water
- Deuterium oxide is an important part of heavy water nuclear reactors, where it is used as a coolant or neutron moderator.
- It is used for the production of heavier hydrogen isotope deuterium.
- Deuterium oxide is used as the source of deuterium for preparing specifically labeled isotopologues of organic molecules.
- It is used in nuclear magnetic resonance spectroscopy (NMR) when we use water as a solvent. Deuterium oxide is used instead of normal water because the signal from light-water solvent molecules interferes with the signal from the molecule dissolved in it.
- It is used instead of water when collecting FTIR spectra of proteins in solution. Water creates a strong band that overlaps with the amide I region of proteins. The band from deuterium oxide has shifted away from the amide I region.
- Tritium is formed when the deuterium present in heavy water captures a neutron and is used as an active substance to control nuclear fusion reactions.
- It is used as a tracer to study the mechanism of respiration, and photosynthesis processes.
- In the medical field, the metabolic rate in humans and other animals is tested with the help of a mixture of heavy water and heavy-oxygen water.
References
Heavy Water (D2O) — Chemical, Uses — Priyamstudycentre.com
