Question

Heavy water is obtained by (a) boiling water (b) heating \(\mathrm{H}_{2} \mathrm{O}_{2}\) (c) prolonged electrolysis of \(\mathrm{H}_{2} \mathrm{O}\) (d) All of these.

Short answer

Heavy water is obtained by prolonged electrolysis of H2O.

Step-by-step solution

Understanding Heavy Water

Understand that Heavy Water (D2O) is water in which the hydrogen atoms (H) have been replaced by deuterium isotopes (D), which are twice as heavy as regular hydrogen atoms.

Analyzing the Options

Analyze each given option to determine which process could feasibly produce deuterium-enriched water.

Option A: Boiling Water

Rule out boiling water, as it merely involves the phase change from liquid to gas and does not alter the isotopic composition of hydrogen in water.

Option B: Heating H2O2

Rule out heating H2O2 (hydrogen peroxide), as it is a different compound from water and decomposes into water and oxygen when heated.

Option C: Prolonged Electrolysis of H2O

Confirm that during the prolonged electrolysis of water, the lighter isotope of hydrogen (protium, 1H) is preferentially released at the anode, which leads to the enrichment of deuterium in the remaining water, thus yielding heavy water.

Conclusion

Determine that the correct answer is the one which involves changing the isotopic composition of hydrogen in water to increase the proportion of deuterium, which is 'C' prolonged electrolysis of H2O.

Key concepts

Deuterium Enrichment

Deuterium enrichment refers to the process of increasing the concentration of the deuterium isotope, or heavy hydrogen (symbolized as 'D'), within a sample of hydrogen. Natural water contains a small fraction of deuterium atoms, about 0.015% of all hydrogen atoms. For certain scientific and industrial applications, such as nuclear reactors and NMR spectroscopy, water with a higher deuterium content, known as heavy water (D2O), is required.

One method for enriching deuterium in water is through the process of prolonged electrolysis. During electrolysis, water molecules are split into oxygen, which collects at the anode, and hydrogen, which collects at the cathode. Because the lighter isotope of hydrogen, protium (1H), converts to gas and is released more readily than deuterium, the process can be manipulated to gradually increase the proportion of deuterium in the remaining liquid.

It is important for educational purposes to recognize that not all methods of processing water can lead to an increase in deuterium content. For instance, simply boiling water will not enrich it in deuterium; it only changes the state of the water from liquid to vapor.

Prolonged Electrolysis of Water

Prolonged electrolysis of water is a practical method for producing heavy water, which is a form of water containing a higher ratio of deuterium atoms to protium atoms compared to normal water. The key to this method is that the two isotopes of hydrogen have different physical properties. Deuterium has a greater mass compared to protium, and so when an electric current is passed through water during electrolysis, protium is preferentially oxidized at the anode and released as gas from the solution at a faster rate than deuterium.

Over time, this preferential release of protium leads to an increase in the proportion of deuterium in the water that remains. This process is slow and requires a significant amount of electrical energy, which is why it is described as 'prolonged'. It's worth noting that in an educational setting, making this distinction is crucial for students to understand the relationship between the process duration and effectiveness in deuterium enrichment. To enhance learning, it's helpful to present a visual or simulation of the electrolysis process, which can demonstrate how after several cycles, the water becomes 'heavy' as it becomes enriched with deuterium. This concept underpins the production of heavy water used in certain types of nuclear reactors.

Isotopic Composition of Water

Understanding the isotopic composition of water is foundational in grasping the concept of heavy water production. Water (H2O) is composed of hydrogen and oxygen, but the isotopes of hydrogen present in natural water can vary. Most hydrogen atoms are the isotope protium, with just one proton in the nucleus. Deuterium, another isotope, has both a proton and a neutron in its nucleus, which makes it twice as heavy and much less abundant.

The isotopic composition is altered in the production of heavy water by increasing the relative amount of deuterium isotopes. Educational comparisons, such as contrasting the natural abundance of deuterium in water (approximately 1 part per 6,700 parts) with the enriched levels in heavy water, can be especially valuable for student comprehension.

To foster a deeper understanding, teachers or educational content creators could provide exercises that involve calculating the enrichment factor or predicting how the isotopic composition will change after certain processes, like the aforementioned prolonged electrolysis. This reinforces the concept that while all water contains deuterium, the process of electrolysis is unique in its ability to concentrate deuterium to levels where the biological and chemical properties of the water are altered.