Understanding Heavy Water Production

Heavy water, chemically represented as \(D_2O\), is a form of water that contains a larger than normal proportion of the hydrogen isotope deuterium (D). Unlike ordinary water (\(H_2O\)), which contains protium (\(^1H\)), heavy water contains deuterium (\(^2H\)). Deuterium is heavier than protium because its nucleus contains one proton and one neutron, whereas protium has only one proton.

How is Heavy Water Made?

The question asks about the production of heavy water. Let's analyze the options provided to understand the process.

1. Dissolving salts of heavy metals in distilled water
2. Repeated distillation and condensation of water
3. Burning deuterium in oxygen
4. By burning the heavier isotope of oxygen in hydrogen

Based on chemical principles, the most direct way to synthesize pure heavy water (\(D_2O\)) is by combining deuterium gas (\(D_2\)) with oxygen gas (\(O_2\)). This process is analogous to how ordinary water (\(H_2O\)) is formed by burning hydrogen gas (\(H_2\)) in oxygen.

Synthesis by Burning Deuterium in Oxygen

The chemical reaction for the synthesis of heavy water by burning deuterium in oxygen is:

\(2D_2(g) + O_2(g) \rightarrow 2D_2O(l)\)

In this reaction, two molecules of deuterium gas react with one molecule of oxygen gas to produce two molecules of heavy water. This method can produce highly pure heavy water, making it a viable process, especially for creating the initial stock of pure \(D_2O\).

Analyzing Other Options

• Dissolving salts of heavy metals in distilled water: This process would create a solution of heavy metal salts in water. It does not produce heavy water (\(D_2O\)). Heavy metals are elements like lead or mercury, unrelated to the isotopic composition of water.
• Repeated distillation and condensation of water: Ordinary water naturally contains a small amount of heavy water (about 1 part in 6400). Techniques like fractional distillation or electrolysis can be used to *enrich* the concentration of heavy water from natural water. These are methods of separation and concentration, not synthesis from elemental components. While repeated distillation can slightly increase the concentration of heavy water because \(D_2O\) has a slightly higher boiling point than \(H_2O\), it is a separation process and less efficient for producing pure \(D_2O\) compared to synthesis from pure deuterium.
• By burning the heavier isotope of oxygen in hydrogen: The heavier stable isotopes of oxygen are \(^{17}O\) and \(^{18}O\). Burning ordinary hydrogen (\(H_2\)) with oxygen containing these heavier isotopes would produce water molecules like \(H_2^{17}O\) or \(H_2^{18}O\). These are isotopically different forms of water, but they are not heavy water (\(D_2O\)), which is defined by having deuterium atoms replacing protium atoms.

Therefore, the most accurate description among the options for how heavy water is made is by burning deuterium in oxygen.

Conclusion on Heavy Water Production

Based on the analysis of the options, the method that results in the production of heavy water by combining its elemental components is the burning of deuterium in oxygen. This process directly synthesizes \(D_2O\).

Revision Table: Heavy Water Facts

Additional Information on Heavy Water

Heavy water has several important applications, primarily due to its properties being slightly different from ordinary water. Some key uses include:

• Nuclear Reactors: Heavy water is used as a neutron moderator in some types of nuclear reactors (like CANDU reactors). Its deuterium atoms are much less likely to absorb neutrons compared to the protium atoms in ordinary water, helping to sustain the nuclear fission chain reaction more efficiently, especially when using natural uranium fuel.
• NMR Spectroscopy: Deuterated solvents (including heavy water) are commonly used in Nuclear Magnetic Resonance (NMR) spectroscopy. Deuterium nuclei have different magnetic properties than protium, and using \(D_2O\) allows scientists to study hydrogen atoms in dissolved samples without interference from the signal of the solvent's own hydrogen atoms.
• Isotopic Tracer: Heavy water can be used in biological and chemical research as an isotopic tracer to study reaction mechanisms and metabolic pathways.

While burning deuterium in oxygen is a synthetic route to produce pure heavy water, large-scale industrial production often involves processes that enrich the small amount of \(D_2O\) present in natural water. Common enrichment methods include distillation, electrolysis, and chemical exchange processes.