Question

Heavy water is used as (a) drinking water (b) detergent (c) washing water (d) a moderator.

Short answer

Heavy water is used as a moderator (d).

Step-by-step solution

Understanding the Exercise

The exercise is asking for the common use of heavy water, which is chemically known as deuterium oxide (D2O). It is important to know that heavy water has specific applications due to its unique physical properties.

Eliminating Incorrect Options

Heavy water is not typically used for drinking (option a), as a detergent (option b), or for washing (option c). While theoretically it could be used for these purposes, its unique properties and higher costs make it impractical for such common uses.

Identifying the Correct Option

The correct use of heavy water is as a moderator (option d) in nuclear reactors. A moderator is a substance that slows down neutrons so that they can sustain a controllable nuclear chain reaction.

Key concepts

Nuclear Reactor Moderator

Heavy water is well-known for its critical role in nuclear reactors, serving as a nuclear reactor moderator. But what exactly does this mean? In the heart of a nuclear reactor, a process called nuclear fission occurs, whereby the nuclei of atoms are split, releasing a substantial amount of energy. This process also releases additional neutrons which can then go on to split more nuclei, leading to a chain reaction. For the reaction to be controlled and sustained, the speed of these neutrons must be reduced, as slower neutrons are more likely to cause further fission in certain types of fuel, like uranium-235.

Heavy water, which consists of the hydrogen isotope deuterium, is exceptionally efficient at slowing down neutrons without absorbing them. This property makes D2O an ideal moderator material. Some of the world's nuclear reactors utilize heavy water to achieve a controlled environment for energy production. Without a moderator like heavy water, the chain reaction within a reactor would be too fast and could lead to a dangerous, uncontrolled release of energy.

Properties of Heavy Water

When discussing heavy water, we delve into the specific properties of heavy water that make it unique and highly valuable in scientific applications. Heavy water, chemically known as D2O, is similar to regular water but with both of the hydrogen atoms replaced by deuterium, which is a heavier isotope of hydrogen containing an extra neutron. This simple difference results in several interesting physical properties.

For one, heavy water has a higher boiling point and a higher freezing point than ordinary water. It's also denser; for a given volume, heavy water weighs more than regular water. However, one of its most notable properties is the low absorption cross-section for neutrons, making it an excellent candidate for moderating a nuclear reaction, as mentioned earlier. This means it can slow down neutrons without capturing them, which is a vital characteristic in nuclear reactor maintenance. Due to its higher cost and specialized nature, heavy water is not suitable for everyday uses such as drinking or cleaning.

Deuterium Oxide (D2O)

Deuterium Oxide, commonly known as D2O or heavy water, is a form of water where the two hydrogen atoms are the isotope deuterium, rather than the more common protium isotope. Deuterium is twice as heavy as protium, hence the name 'heavy water'. Apart from its utilization as a reactor moderator, heavy water has other scientific uses due to its unique characteristics.

For instance, D2O is used in NMR spectroscopy, where it provides a deuterium signal that can be differentiated from hydrogen, aiding in more complex analysis. In addition, it plays a role in certain types of biochemical experiments to trace reactions and pathways in living organisms, as deuterium can replace the hydrogen in biological molecules. This can give researchers insight into the mechanisms of life at a molecular level. However, due to its physiochemical properties, heavy water is not consumed like regular water, marking the distinction that while all heavy water is essentially water, not all water is suitable for everyday human use.