Heavy Water is a form of water that contains a larger amount of the hydrogen isotope deuterium, than is found in normal water.

Heavy water is a compound composed of deuterium (an isotope of hydrogen denoted by ‘2H’ or ‘D’) and oxygen. It is also known as deuterium oxide and is represented by the chemical formula D2O.

Table of Contents

Properties of Heavy Water

Preparation of Heavy Water

Types of Heavy Water

Important Reactions of Heavy Water

Uses of Heavy Water

Heavy water (D2O) has a greater molar mass than regular water (H2O) due to the higher atomic mass of deuterium compared to protium. This leads to slightly different chemical and physical properties between the two.

Properties of Heavy Water

| Heavy Water (Deuterium Oxide) | D2O |

| Molecular Mass | 20.02 g/mol |

| Density | 1.107 g/mL |

| Dipole Moment | 1.87 D |

| Melting Point | 3.82°C |

| Boiling Point | 101.4°C |

Physical Properties

Heavy water has a colourless appearance at STP.

At room temperature, it exists as an odorless liquid.

An ice cube made of deuterium oxide will sink in normal water due to its density being approximately 11% greater than that of H2O.

Heavy water and normal water form a homogeneous mixture when mixed.

Chemical Properties

The different atomic masses of hydrogen isotopes result in different chemical behaviors, as seen in atomic masses.

The presence of high quantities of deuterium can have a negative impact on the solvent properties of water, thus adversely affecting biological systems.

Normal water dissociates to a greater extent than heavy water.

At a given temperature, the concentration of D+ ions in a D2O sample is generally lower than the concentration of H+ ions in an H2O sample.

⇒Further Reading: Physical and Chemical Properties of Water

Methods of Preparation

Heavy water is prepared by the prolonged electrolysis of water containing alkali.

Electrolyte: Water containing NaOH.

Cathode: Steel vessel.

Anode: A sheet of Nickel with holes.

The important features of heavy water, which is the leftover product of neutralizing seven alkalies by the passage of CO2 gas through electrolysis, are listed below.

The nucleus of a deuterium atom holds one proton and one neutron, making it roughly twice as heavy as protium (the isotope of hydrogen denoted by 1H, which is present in normal water).

Approximately 89% of the molecular mass of a water molecule is attributed to oxygen, so the molecular mass of D2O is not significantly higher than that of H2.

The density of heavy water is approximately 11% greater than that of normal water.

The bond between deuterium and oxygen in D2O is stronger than the bond between protium and oxygen in H2.

D2O is not radioactive in nature because the deuterium atom does not undergo radioactive decay, which is a process of spontaneous nuclear decay.

High doses of heavy water can be toxic to many organisms.

In 1932, the first production of deuterium oxide (D2O) occurred. It is used as a neutron moderator and coolant in pressurized heavy water reactors (PHWR). The term ‘heavy water’ generally refers to D2O, but other forms of “heavy” water also exist.

⇒ Check out this link to learn about the hardness of water, types and treatment.

Types of Heavy Water

Semi-Heavy Water (D2O)

This form of heavy water is denoted by the formula HDO and is made up of one protium, one deuterium, and one oxygen atom.

Water molecules tend to exchange hydrogen atoms between each other, which implies that HDO can be found in samples of water containing both protium and deuterium.

A water sample containing an equal ratio of protium and deuterium consists of 50% semi-heavy water, 25% normal water, and 25% heavy water.

In this sample, there is a dynamic equilibrium between HDO, D2O, and H2.

Heavy-Oxygen Water

Water containing heavier isotopes of water, such as 17O and 18O, is referred to as “heavy-oxygen water.”

Its density is higher than regular water, making it a form of heavy water.

Heavy-oxygen water containing the 18O isotope of oxygen is utilized in the production of the 18F isotope of fluorine, as well as in radiotracers and radiopharmaceuticals.

Tritiated Water (T₂O)

Tritiated water (also known as tritiated hydrogen or hydrogen-3 water, and usually denoted as HTO or T_2O) is a radioactive form of water that contains tritium (denoted by T or 3H) instead of protium.

It is commonly referred to as “super-heavy water” and is represented by the formula D$_2$O.

Tritiated water can be used to determine the total volume of water in a body. Find out more.

The molar mass of T2O is 22.03 grams per mole and its density is 1.85 g/mL.

Some Important Reactions of Heavy Water

Electrolysis: 2H${2}$O → 2H${2}$ (Deuterium) + O$_{2}$

Reactions with Metals: 2Na + 2D₂O → 2NaOD (Sodium Deuteroxide) + D₂

Reactions with Non Metals: D2O + Cl2 → DCl + HClO

Reactions with Metal Oxide:

MgO + D2O → Mg(OD)2

Reactions with Non-Metal Oxides:

SO3 + D2O → D2SO4 (Deutero sulphuric acid)

Reactions with Magnesium Nitride:

Mg3N2 + 6D2O → 3Mg(OD)2 + 2ND3 (Deutero Ammonia)

Reactions with Calcium Phosphide:

3Ca3P2 + 6D2O → 3Ca(OD)2 + 2PD3 (Deutero Phosphide)

Reactions with Calcium Carbide: CaC₂ + 2D₂O → Ca(OD)₂ + C₂D₂ (Deutero Acetylene)

Reactions with Aluminium Carbide:

4Al4C3 + 12D2O → 4Al(OD)3 + 3CD4 (Deutero methane)

Some other uses include:

Heavy water is used in Nuclear Magnetic Resonance Spectroscopy.

It is used as a moderator in certain types of nuclear reactors.

In the medical field, it is used to measure the metabolic rate of humans.

Uses of Heavy Water

As previously mentioned, deuterium oxide (heavy water) is an essential component in heavy water nuclear reactors, serving as both a coolant and a neutron moderator. Additionally, heavy water has several other important applications, which are outlined below.

Heavy water (D2O) is used for the preparation of Deuterium (D).

As a tracer to study the mechanism of respiration and photosynthesis.

D2O is utilized in NMR (Nuclear Magnetic Resonance) Spectroscopy, which is employed to observe the magnetic fields surrounding the nuclei of atoms.

Isotopologues of many organic compounds can be synthesized using deuterium oxide.

Heavy water (D₂O) is often used instead of normal water (H₂O) in IR (infrared) spectroscopy.

As a moderator in the nuclear reactor, I am responsible for slowing down the fast-moving neutrons so that they can react with the 235U isotope instead of the 238U isotope.

The metabolic rate in humans and animals is tested using a mixture of D2O and heavy-oxygen water.

Tritium, which is used in controlled nuclear fusion reactions, is formed when a neutron is captured by the deuterium present in heavy water.

Is Drinking Heavy Water Dangerous?

Heavy water (deuterium oxide) is not toxic and can be safely consumed in small quantities. However, consuming large amounts of heavy water can be dangerous due to its potential to interfere with normal metabolic processes.

Heavy water is not always associated with radioactive materials and nuclear reactors. In fact, pure heavy water is not radioactive and not particularly harmful if consumed in small quantities. However, if large amounts are ingested or if consumed for a prolonged period of time, serious poisoning may occur, leading to symptoms such as dizziness and decreased blood pressure.

Electrolysis in Molten State

![Electrolysis in Molten State]()

Frequently Asked Questions (FAQs)

The chemical formula of heavy water is D2O.

The boiling point of heavy water (D2O) is 101.42 °C.

The boiling point of heavy water (D2O) is 101.4°, which is slightly higher than that of normal water (H2O). Heavy water is prepared through the process of electrolysis.

Electrolyte: Alkali water

Anode: Positively charged electrode

Cathode: Negatively charged electrode

Electrolyte: Alkaline Water

Anode: Nickel sheet with holes

Anode: Steel vessel.### Which is the radioactive form of Uranium-238?

T₂O is the radioactive form of water.