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Heavy water-Physical properties, Chemical properties, Preparation, Types of heavy water, Uses, Practice problems, FAQ

Everyone is aware of the most essential component of life,i.e. Water. You will be surprised to know one thing, there is one more type of water present which is called heavy water. You all get surprised after listening to the name ‘heavy water’. Isn’t it heavy or what actually it is! Harold Urey, a Nobel Laureate from the United States, discovered the isotope deuterium in 1931 and was able to concentrate it in the water later. Let’s study this in detail!

Table of content

  • What is heavy water?
  • Physical properties
  • Chemical properties
  • Preparation of heavy water
  • Types of heavy water
  • Uses of heavy water
  • Practice problems
  • Frequently asked questions-FAQ

What is heavy water?

Heavy water is a mixture of oxygen and deuterium, a heavier isotope of hydrogen symbolized by the letter 'D’' The molecular formula D2O stands for heavy water, commonly known as deuterium oxide.

Heavy water is generally formed due to the combination of of oxygen and deuterium. Deuterium is an isotope of hydrogen which is generally heavier than other isotopes of hydrogen. “D” letter is used to symoblize deuterium and the molecular formula assigned for deuterium oxide which is commonly called as heavy water is D2O.

Physical Properties

  • D2O has a molar mass of 20.02g mol-1.
  • The molar mass of D2O (heavy water) is 20.02 g mol-1.
  • Density of heavy water is 1.107 g mL-1 at STP 
  • Dipole moment of heavy water comes out to be 1.87 D at STP
  • Boiling point of heavy water is 101.4℃ at STP
  • The melting point of heavy water is 3.82℃ at STP
  • At STP, heavy water appears to be colorless.
  • Heavy water seems colourless at STP.
  • It occurs as an odorless liquid at normal temperature.
  • At room temperature (298 K), it behaves as an odourless liquid.
  • An ice cube produced of deuterium oxide will sink in regular water because its density is approximately 11% higher than that of H2O.
  • Due to its slightly higher density than water (about 11% higher), an ice cube made of deuterium oxide(D2O) will sink in ordinary water.
  • When mixed with regular water, heavy water makes a homogenous combination.

Chemical properties: 

Because of their differing atomic weights, hydrogen isotopes have varied chemical properties.

The chemical characteristics of hydrogen isotopes vary due to their various atomic weights.

Changes in the solvent properties of water caused by excessive levels of deuterium can have a negative impact on biological systems. Deuterium levels that are too high can alter water's properties as a solvent, which can be harmful to biological systems. When compared to heavy water, normal water dissociates to a greater extent. The concentration of D+ ions in a D2O sample is often lower than the concentration of H+ions in a H2O sample at a given temperature.

Normal water dissociates more than heavy water when compared to each other. At a given temperature, the concentration of D+ ions in a D2O sample is frequently lower than the concentration of H+ ions in an H2O sample.KW for water is 10-14 at 25℃ whereas for heavy water it is 1.3510-15 at 25℃.

Some important reactions of D2O are:
Reaction of heavy water with metal: When D2O reacts with sodium metal it gives sodium deuteroxide NaOD. 

2Na(s) +2D2O(l)NaOD(s)+D2(g)

Reactions of heavy water with Non-Metals: When D2O reacts with non-metal like chlorine it gives deuterium chloride.
Reactions with heavy water by Non-Metal Oxides: When D2O reacts with non-metal oxides and it gives Deutero acids.
SO3(l)+D2O(l)D2SO4(l) (Deutero sulphuric acid)
Reactions of heavy water with Magnesium Nitride: When D2O reacts with magnesium nitride, Deutero ammonia is formed.
Mg3N2(s)+6D2O(l)3Mg(OD)2(s)+2ND3(g)(Deutero Ammonia)
Reactions with Calcium Phosphide: When D2O reacts with calcium phosphide deutero is formed.
Ca3P2(s)+6D2O(l)3Ca(OD)2(s)+2PD3(g)(Deutero Phosphide)

Preparation of Heavy water:
1) By using electrolysis method: Heavy water can also be separated from ordinary water by electrolysis of ordinary water. It was that electrolysis of H2O occurs about 6 times more quickly than electrolysis of it when electrolysis of ordinary water. Therefore, upon electrolysis of ordinary water, the ratio of heavy water in it increases gradually.

By electrolysis of regular water, heavy water can also be separated from regular water. When ordinary water is electrolyzed, it was found that H2O does so approximately six times more quickly than it does. As a result, the proportion of heavy water in ordinary water gradually increases after electrolysis.

2) By using exchange reactions: Exchange operations can also produce heavy water,D2O. The hydrogen atoms in H2S gas are replaced by deuterium atoms from D2O present in the water as it passes through heated water, for example. D2S is thus added to H2S as a result. When this D2S-enriched H2S is passed through cold water, and the deuterium from the D2S and the hydrogen from the H2O swap places again. The technique is repeated, and the D2O concentration in the cold water is gradually increased.

3) By using fractional distillation: The separation of heavy water from ordinary water may be affected by fractional distillation. In this approach, the difference in boiling points of regular water (100°C) and heavy water (101.42°C) is utilized. As a result, the lighter component separates from the heavier water-rich waste first (D2O).

Types of Heavy water:

1. Oxygenated Water

  • Heavy-oxygen water is defined as water that contains heavier isotopes of oxygen

(17O and 18O)

  • Water with heavier oxygen isotopes (17O and 18O) is known as heavy-oxygen water.
  • Because it has a larger density than conventional water, it is classified as heavy water.
  • It is referred to as heavy water because it is denser than regular water.
  • The synthesis of the isotope of fluorine requires heavy-oxygen water containing the isotope of oxygen 18O
  • Heavy-oxygen water containing the isotope of oxygen 18Ois necessary for the synthesis of the fluorine isotope 18F.
  • It's also used in radiopharmaceuticals and radiotracers.
  • Additionally, it is a component of radiotracers and radiopharmaceuticals.

2. Semi-Heavy water: 

  • Water that is partial heavy is known as semi-heavy water (HDO)
  • This type of heavy water has the formula HDO and contains one protium, one deuterium, and one oxygen atom.
  •  Hydrogen atoms tend to be exchanged between water molecules. This means that HDO can be found in both protium and deuterium-containing water samples.

3. Titrated water: 

  • Tritiated Water (T2O) is a radioactive version of water that contains tritium instead of protium (denoted by T or ). It's also known as super-heavy water. 
  • The total volume of water in a body can be calculated using tritiated water. T2O has a molar mass of 22.03 g mol-1 and a density of 1.85 g mL-1

Uses of Heavy water:
Heavy Water's Applications are:

  • Heavy water is used as a germicide and bactericide.
  • The structure and basicity of many oxyacids were investigated using heavy water's exchange reaction characteristic.
  • 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. 

ar reactors, heavy water serves as a moderator. The fission of uranium atoms requires neutrons at a slow speed. 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.

Practice Problem:
Q1. Mention a chemical reaction where DeuteroAcetylene is formed.
Solution: When D2O reacts with calcium carbide DeuteroAcetylene is formed. Below is the mentioned reaction:
CaC2+2D2OCa(OD)2+C2D2(Deutero Acetylene)

Q2. Explain the biological effects of Heavy water.
Solution: In heavy water, plants and animals develop more slowly. Little fish die because seeds do not germinate in clean heavy water. Water with a high percentage of D2O is also poisonous.

Q3.What do you understand about the term deuterolysis?
Solution: Water hydrolyzes certain inorganic salts. This process is called electrolysis. When heavy water is utilized, similar processes are known as salt deuterolysis.

Q4.What happens when aluminium chloride is treated with heavy water?
Solution: When D2O reacts with aluminium chloride, Deutero chloric acid is formed. Below is the mentioned reaction:
AlCl3+3D2OAl(OD)3+3DCl(Deutero Chloric acid)

Frequently asked questions-FAQ

Q1. Is heavy water safe for drinking?
Answer: Heavy water isn't fully safe to drink just because it isn't radioactive. The difference in the mass of the hydrogen atoms and how strongly they form hydrogen bonds would alter the metabolic reactions in your cells if you drank enough heavy water.

Q2.Which is more polar, D2O or H2O?
Answer:  Deuterium is more electronegative than hydrogen also the dipole moment of D2O will increase as the difference in electronegativity between Deuterium and oxygen increases. Therefore D2O is more polar than H2O.

Q3. What is the nature of D2O? Acidic or basic?
Answer: The pH at room temperature obtained for heavy water D2O is greater than that of normal water. pH of D2O is around 7.44, which indicates that D2O is basic in nature.

Q4. Will it be easier to sail a boat in heavy water than in normal water?
Answer: Because heavy water is heavier, (i.e density = 1.107 g mL-1) than 'regular' water
(i.e density = 1 g mL-1) , resulting in a larger upthrust for the same displacement. Hence, a boat in a sea of deuterium can float higher than one in normal water.

Q5. What is Deuterium Depleted Water?
: Water containing Deuterium less than its natural abundance ( <125 ppm) is called Deuterium Depleted Water. It is getting popularized as adjuvant therapy for cancer.

Deuterium Depleted Water is water that contains less deuterium than it does naturally (<125 ppm). As a form of adjuvant cancer treatment, it is becoming more well-known.

Q6. What is a Moderator?
: Moderator is required in a Nuclear reactor to slow down the neutrons produced during the fission reaction so that the chain reaction can be sustained. Heavy Water is an excellent moderator due to its high moderating ratio and low absorption cross-section for neutrons.

In order for the chain reaction to continue, a moderator is needed in a nuclear reactor to slow down the neutrons created during the fission reaction. Due to the high moderating ratio and low neutron absorption cross-section, heavy water makes an excellent moderator.

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