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Heavy water (D2O) is essentially deuterium-based water that is composed of oxygen and deuterium, a heavier isotope of hydrogen. It is also known as Deuterium oxide.
- Deuterium is a hydrogen isotope with twice the mass of regular hydrogen.
- Heavy water has a molecular weight of about 20, whereas ordinary water has a molecular weight of about 18.
- It was first produced in 1932 after the discovery of deuterium.
- The compound is 10.6% denser and has a higher melting point.
- It consists of two deuterium atoms in place of the two protium atoms.
- The compound is less dissociated at a given temperature.
- Heavy water is used in nuclear magnetic resonance, infrared spectroscopy, and neutron moderation.
Key Terms: Heavy Water, Deuterium, Oxygen, Hydrogen, Electrolysis, Fractional Distillation, isotope, Molecular Weight, Atoms, Ions, Electrolytic Cell, Homogenous Mixture, Semi-Heavy Water, Heavy-Oxygen Water
What is Heavy Water?
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Heavy water is an organic compound that is composed of deuterium. It is also known as deuterium oxide with a molecular weight of 20 (the sum of twice the atomic weight of deuterium, which is 2, plus the atomic weight of oxygen, which is 16).
- Heavy water is denoted by 2H2O and D2O.
- Due to the presence of a heavier isotope of hydrogen, the water has different nuclear properties.
- As the mass of the compound increases, the physical and chemical properties also change.
- The compound is used in nuclear reactors.
- It is used for testing the metabolic rate in humans and animals.
- Bacteria can survive in a heavy hydrogen environment.
- Heavy water is used in the design of nuclear weapon design for boosting fission weapons.
Heavy Water
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Types of Heavy Water
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Heavy water is divided into three categories which are as follows:
Semi-Heavy Water
Semi-Heavy Water is denoted as HDO. It is formed when water contains light hydrogen (protium, 1 H) and deuterium (D or 2 H). This is due to the rapid exchange of hydrogen atoms (hydrogen-1 and deuterium) between water molecules.
- It contains 50% semi-heavy water, 25% normal water, and 25% heavy water.
Heavy-Oxygen Water
Heavy-oxygen water is a type of heavy water that contains heavier isotopes of water, such as 17O and 18O. The compound is used in used in radiotracers and radiopharmaceuticals.
- It is termed "heavy water" because it is denser than ordinary water.
- The compound also lacks the deuterium that gives D2O its unique nuclear and biological features.
Tritiated Water
Tritiated water includes tritium (3H) instead of protium (1H) or deuterium (2H), and because tritium is radioactive, so is tritiated water. It is also known as super-heavy water.
Properties of Heavy Water
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The properties of heavy water is divided into physical and chemical properties which are as follows:
Physical Properties
The physical properties of heavy water are as follows:
- At standard temperature and pressure, heavy water appears to be colorless.
- It exists as an odorless liquid at room temperature.
- An ice cube produced of deuterium oxide will sink in regular water.
- Its density is approximately 11% higher than that of H2O.
- When heavy water is mixed with regular water, it makes a homogenous mixture.
The physical properties of heavy water are tabulated below:
| Category | Data |
|---|---|
| Heavy Water (Deuterium Oxide) | D2O |
| Molecular Mass | 20.02 grams/mole |
| Dipole Moment | 1.87 D |
| Density | 1.107 g/mL |
| Boiling Point | 101.4oC |
| Melting Point | 3.82oC |
Chemical Properties
The chemical properties of heavy water are as follows:
Reaction Rate
The reactions involving D2O are slower than those using H2O.
Electrolysis
Deuterium can be obtained at the cathode when heavy water is electrolyzed.
Alkali and Alkaline Metals Effects
The reaction yields di-deuterium, however it proceeds at a snail's pace.
Activity of Metallic Oxides
The reaction takes a long time to complete and creates deuteroxides.
Effect of Non-Metallic Oxides
Deutero Acids with corresponding deutero acids are produced. Phosphorus pentoxide and sulphur trioxide are nonmetallic oxides that dissolve easily in heavy water.
Action with Metallic Nitrides, Phosphides and Arsenides
When heavy water reacts with metallic nitrides, phosphides, and arsenides, deutero ammonia, deutero phosphine, and deuteroarsine are released (respectively).
Formation of Deuterates
Heavy water of crystallization is known to interact with a variety of chemicals, resulting in the formation of deuterates.
Exchange Reaction
When compounds are treated with heavy water, active hydrogen atoms are transferred either partially or completely.
Methods of Preparation
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Heavy water is mainly prepared using either of the two techniques – Prolonged electrolysis or Fractional distillation which are as follows:
By Prolonged Electrolysis
The process of prolonged electrolysis is as follows:
- Protium is generated when ordinary water is electrolyzed.
- H+ ions have greater mobility than D+ ions; protium is easily liberated in H2O.
- This is due to the fact that it is smaller.
They also have a lower discharge potential, allowing H+ ions to discharge more easily at the cathode. Furthermore, hydrogen atoms are more likely than deuterium atoms to form molecular hydrogen.
- As the electrolysis progresses, the concentration of heavy water in ordinary water rises.
- When there is very little volume left, virtually pure heavy water can be obtained.
- Brown, Degget, and Urey devised an electrolytic cell for heavy water preparation.
- It is made up of a steel cell that is 45 cm long and 10 cm wide.
- Many of these cells are used in various stages of water electrolysis.
By Fractional Distillation
The boiling points of regular and heavy water differ by a minor amount. The use of fractional distillation for the manufacture of heavy water is based on this principle.
- Normal water has a boiling point of 373K.
- On the other hand, heavy water has a boiling point of 374.42K. (at normal atmospheric pressure).
Uses of Heavy Water
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Uses of heavy water are as follows:
Nuclear Magnetic Resonance
Deuterium oxide is employed when water is employed as a solvent in nuclear magnetic resonance spectroscopy, and the nuclide of interest is hydrogen.
- The reason is the signal from the light-water molecules interacts with the signal from the dissolved molecule of interest.
Organic Chemistry
Deuterium oxide is frequently utilized as a source of deuterium in the preparation of isotopologues of organic molecules that are specially labelled.
- C-H bonds are close to ketonic carbonyl groups.
- For example, it can be exchanged by C-D bonds via acid or base catalysis.
Infrared Spectroscopy
When collecting FTIR spectra of proteins in solution, deuterium oxide is frequently employed instead of water. H2O forms a broad band that stretches across the amide I region of proteins.
- The D2O band has been moved away from the amide I area.
Neutron Moderator
Heavy water is employed as a neutron moderator in nuclear reactors, slowing down neutrons so that they are more likely to react with fissile uranium-235 rather than uranium-238.
- The process collects neutrons without fissioning.
Metabolic Rate Testing
For a typical and safe test of the mean metabolic rate in humans and animals going about their daily activities, heavy water is mixed with H218O.
Important Reactions of Heavy Water
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Some important reactions of heavy water are as follows:
Reaction with Metals
Alkali and alkaline earth metals react slowly with D2O, releasing heavy hydrogen. Some of the reaction are as follows:
- Sodium Deuteroxide: 2 Na + 2 D2O -- > 2 NaOD + D2
- Calcium Deuteroxide: Ca + 2 D2O -- > Ca (OD)2 + D2
Reaction with Metallic Oxides
Heavy alkalies are formed when metals such as sodium and calcium dissolve in D2O. Some of the reaction are as follows:
Na2O + D2O → 2 NaOD
CaO + D2O → Ca(OD)2
Reaction with Acid Anhydrides
In this, D2O breaks down into heavy hydrogen-containing acids. Some of the reaction are as follows:
- Deutero Sulphuric Acid: SO3 + D2O -- > D2 SO4
- Deutero-Phosphoric Acid: P2O5 + 3D2O -- > 2D3 PO4
Reaction with Other Chemicals
Deuterates are formed when salt and other chemicals are combined, whose products include Cu SO4. 5 D2O, Na2SO4. 10D2O, NiCl2.6D2O
Exchange Reactions
When hydrogen-containing substances are treated with D2O, the hydrogen is exchanged for deuterium.
NaOH + D2O -> NaOD + HOD
NH4 Cl + 4D2O -- > ND4 Cl + 4HOD
Reaction with Aluminium Carbide
When aluminium carbide reacts with heavy water, then, it will form deutero methane. The reaction is as follows:
Al4C3 + 12D2O → 4Al(OD)3 + 3CD
Reaction with Calcium Carbide
When calcium carbide reacts with heavy water, then, it will form deutero acetylene. The reaction is as follows:
CaC2 + 2D2O → Ca(OD)2 + C2D2
Reaction with Calcium Phosphide
When calcium phosphide reacts with heavy water, then, it will form deutero phosphide. The reaction is as follows:
Ca3P2+6D2O → 3Ca(OD)2+2PD3
Heavy Water Health Hazards
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Heavy water is hazardous to humans, plants, and animals because it slows down many responses. It also slows down the rate at which reactions occur to them. As a result,
- Tobacco seeds do not develop in standing water.
- When tadpoles, tiny fish, and mice are fed pure heavy water, they die.
- The growth of living organisms such as plants and animals is slowed by heavy water.
Read More:
| Class 11 Chemistry Related Concepts | ||
|---|---|---|
| Gay-Lussac’s Law | Sandmeyer Reaction | Enantiomers |
| Oxidizing Agent | Alliphatic Hydrocarbons | Mitsunobu Reaction |
Things to Remember
- Heavy water, also known as deuterium oxide, was first created in 1932, just months after deuterium was discovered.
- The presence of the heavier hydrogen isotope gives heavy water different nuclear properties.
- The increase in mass gives it slightly different physical and chemical properties when compared to normal water.
- Heavy water became a component of early nuclear energy research after the discovery of nuclear fission in late 1938.
- It lacks the characteristic blue colour of light water because of the molecular vibration harmonics.
- The reported incidence of dizziness after consuming heavy water could be explained in part by a drop in blood pressure.
Sample Questions
Ques. Is heavy water healthy for consumption? (2 marks)
Ans. Heavy water is usually associated with nuclear reactors and radioactive materials. Pure heavy water, on the other hand, is not radioactive and is not dangerous to humans in small amounts. It is only damaging or dangerous if big amounts of water are ingested or if heavy water is consumed over an extended period of time. Poisoning can occur, causing symptoms such as dizziness and low blood pressure.
Ques. Where is heavy water found naturally? (2 marks)
Ans. In Canada, the heavy water is not manufactured, but rather it is extracted from the quantity that is found naturally in lake water. The water is separated through a series of towers, using hydrogen sulphide as an agent. Owing to AECLs CANDU programme, Canada is the world's supplier of heavy water.
Ques. When and why is it reported that heavy water utilized in nuclear power plants contains radioactivity? (2 marks)
Ans. By absorbing a neutron in a nuclear reactor, a small amount of Deuterium in Heavy Water is transformed to Tritium. Tritium is a hydrogen isotope with two neutrons in its nucleus that is radioactive. Furthermore, during irradiation, some of the ionic contaminants carried by heavy water as a moderator or coolant become activated. As a result, radioactivity is detected in Heavy Water, which is used in nuclear reactors.
Ques. Is heavy water harmful to health? (3 marks)
Ans. Human health is not harmed by a modest amount of heavy water. In truth, as a natural abundance, the human body has only a few grammes of Heavy Water.
- Heavy Water has been used in small amounts in clinical investigations and treatment in infants, breastfeeding women, and adults with no documented side effects.
- Its toxic effects manifest only when the deuterium content of human fluids exceeds 20%, which is the rarest scenario.
Ques. How is heavy water prepared? (2 marks)
Ans. When water is electrolyzed, hydrogen is freed far faster than deuterium. As a result, H2O bonds are easier to break than D2O bonds (18 times easier). As a result, if the electrolysis is continued until there is only a trace of water left, the residue is pure D2O. One millilitre of heavy water is created when roughly 30 litres of water are electrolyzed.
Ques. Mention the biological properties of heavy water? (3 marks)
Ans: Heavy water is hazardous to humans, plants, and animals because it slows down many responses. It also slows down the rate at which reactions occur to them. As a result,
- Tobacco seeds do not develop in standing water.
- When tadpoles, tiny fish, and mice are fed pure heavy water, they die.
- The growth of living organisms such as plants and animals is slowed by heavy water.
Ques. What is Deuterolysis? (2 marks)
Ans. Some inorganic salts are hydrolyzed by water. Similar processes known as salt Deuterolysis occur when heavy water is used.
AlCl3 + 3D2O → Al(OD)3 + 3DCl
BaS + 2D2O → Ba(OD)2 + D2S
Ques. What are the properties of heavy water? (2 marks)
Ans. D2O is a clear, odourless, and colourless liquid with no flavour or odour. It has a maximum density of –1.1073 gmL–1 at 11.6 °C. Because heavy water is more viscous than regular water, it has a lower salt solubility than regular water. Nearly all physical constants of D2O or higher than H2O are due to the bigger nuclear mass of a deuterium atom than a hydrogen atom, as well as stronger hydrogen bonding in D2O than in H2O.
Ques. What is the purpose of heavy water? (4 marks)
Ans. To eliminate germs and bacteria, heavy water is utilised. The exchange reaction feature of heavy water is used to investigate the structure and basicity of some oxyacids.
- Electrolysis or an interaction with an active metal like sodium produces deuterium from heavy water.
- Heavy water is used as a moderator in nuclear reactors.
- For the fission of Uranium atoms, slow-moving neutrons are required.
- The neutrons are delayed by flowing through heavy water, which acts as a moderator.
- In the study of aromatic electrophilic substitution reactions, metabolic activities, and other processes, heavy water is widely used as a tracer.
Ques. What is the difference between heavy water and hard water? (3 marks)
Ans. The difference between heavy water and hard water are as follows:
| Heavy Water | Hard Water |
|---|---|
| Heavy water consists of oxygen and deuterium. | Hard water consists of bicarbonates, chlorides, and sulfates of calcium and magnesium. |
| The formula is D2O. | The formula is Ca(OH)2 |
| It does not exhibits blue colour of water. | It exhibits blue colour of water. |
Ques: What happens when heavy water reacts with phosphorus pentaoxide? (2 marks)
Ans: Heavy water with dissolved P2O5 decomposes into deuterium and oxygen, which are freed at the cathode and anode, respectively, during electrolysis.
P2O5 + 3D2O -- > 2D3 PO4
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