Question

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

Short answer

-3.8 degrees Celsius

Step-by-step solution

Understanding the Concept

Heavy water, or deuterium oxide \(\mathrm{D}_{2}O\), has different physical properties from ordinary water \(\mathrm{H}_{2}O\). Its melting point is slightly higher than that of ordinary water.

Research the Accurate Freezing Point

Consulting a reliable scientific source, we find that heavy water \(\mathrm{D}_{2}O\) freezes at \( -3.8^\circ \mathrm{C} \).

Compare the Options

Match the freezing point of heavy water from the researched information to the options provided to find the correct answer.

Key concepts

Deuterium Oxide

Deuterium oxide, more commonly known as heavy water, is a form of water in which the two hydrogen atoms, or 'protium', are replaced with deuterium, a heavier isotope. The presence of deuterium, which has one neutron, makes the water denser; hence the name 'heavy water'. Beyond its density, deuterium oxide has unique nuclear properties that make it valuable as a moderator in nuclear reactors, slowing down neutrons to sustain a nuclear chain reaction.

While it's chemically similar to ordinary water, it exhibits distinct physical properties such as a higher boiling point, density, and, crucially for our context, a different freezing point. Since deuterium bonds are slightly stronger than those of protium, D2O remains in its liquid form at temperatures where regular water would freeze.

Physical Properties of Water

Water is a substance with well-documented and studied properties. Its ability to exist in three states—solid, liquid, and gas—makes it unique. The freezing and boiling points of water are fundamental characteristics widely used as reference points in temperature scales. Water has a high specific heat capacity, which allows it to absorb and release a significant amount of heat with little change in temperature.

This property is crucial for the regulation of Earth's climate and also why water is an excellent coolant in various applications. Water is also known for its unusual behavior of expanding upon freezing, resulting in ice being less dense than liquid water, which is why ice floats. These properties, however, can be altered when dealing with isotopic variants of water, such.Water's ability to dissolve a wide range of substances stems from its polarity and is why it's often called the 'universal solvent.' Understanding these properties assists in comprehending the ways in which heavy water deviates from what we consider normal behavior for water.

Melting Point

The melting point, the temperature at which a solid becomes a liquid at atmospheric pressure, is a fundamental physical property of a substance. In the case of water and its isotopic counterparts, the melting point is also its freezing point—the temperature at which the liquid turns into solid. For standard water (H2O), this point is at 0 degrees Celsius (32 degrees Fahrenheit) under normal atmospheric pressure.

The differences in melting points among water's isotopic forms arise due to the variations in atomic bonds. The heavier isotopic version, like deuterium oxide, requires slightly more energy to overcome these stronger bonds, leading to a higher melting and freezing point compared to regular water.In scientific and educational contexts, comparing the melting points of different types of water helps students get a better understanding of intermolecular forces and the effects isotopes may have on physical properties. These concepts are vital for grasping more complex chemical and physical phenomena.