Question

Heavy water \(\left(\mathrm{D}_{2} \mathrm{O}\right)\) freezes at: (a) \(3.8^{\circ} \mathrm{C}\) (b) \(38^{\circ} \mathrm{C}\) (c) \(0^{\circ} \mathrm{C}\) (d) \(-3.8^{\circ} \mathrm{C}\)

Short answer

Heavy water freezes at \(3.8^{\circ} \mathrm{C}\), so the correct choice is (a).

Step-by-step solution

Identify the Substance of Interest

The question is about heavy water, which is chemically denoted as \( \mathrm{D}_{2} \mathrm{O} \). Heavy water is similar to regular water (\( \mathrm{H}_2 \mathrm{O} \)), but it contains deuterium, a heavier isotope of hydrogen.

Recalling Freezing Point of Heavy Water

Unlike regular water, which freezes at \(0^{\circ} \mathrm{C}\), heavy water has a slightly different freezing point due to the presence of deuterium. The text usually references that heavy water freezes at approximately \(3.8^{\circ} \mathrm{C}\).

Select the Correct Answer

Among the options provided, \(3.8^{\circ} \mathrm{C}\) matches the known freezing point of heavy water. Therefore, the correct choice is option (a).

Key concepts

Freezing Point

The freezing point of a substance is a fundamental physical property. It is the temperature at which a liquid turns into a solid. For most substances, including water, this point is quite distinct. However, when we talk about heavy water, or \(\text{D}_2 \text{O}\), it behaves a little differently from regular water. Heavy water freezes at 3.8°C instead of the usual 0°C for normal water. This difference arises because heavy water contains deuterium instead of the regular hydrogen isotopes, thus affecting its physical characteristics.

Deuterium

Deuterium is a special form of hydrogen, commonly referred to as an isotope. An isotope is a variation of an element that has the same number of protons but a different number of neutrons. In the case of deuterium, it contains one proton and one neutron in its nucleus, compared to regular hydrogen, which has only one proton and no neutrons. This subtle change makes deuterium heavier. Hence, when combined with oxygen to form heavy water (\(\text{D}_2 \text{O}\)), it results in a substance with unique properties like an increased freezing point.

Isotopes

Isotopes are fascinating in the field of chemistry. They are atoms of the same element that differ in the number of neutrons they possess. This difference doesn’t affect their chemical behavior significantly but does alter their physical properties. For hydrogen, the isotopes are protium (the most common version with no neutrons), deuterium (one neutron), and tritium (two neutrons). Deuterium, while stable, is heavier, lending to variants like heavy water with altered properties. Being familiar with isotopes helps in understanding the diverse behaviors substances can exhibit solely by atomic changes.

Chemistry Education

Chemistry education is crucial for unraveling the complexities of matter and its interactions. Understanding concepts like isotopes and the properties of different compounds affects how we perceive materials around us. In learning about heavy water and its unique freezing point, students can appreciate the influence of atomic structure on chemical properties. Engaging with such topics enhances problem-solving skills and scientific literacy. By grasping these concepts, students gain insights that aid not only in academic pursuits but in understanding the scientific principles that govern everyday phenomena.