Question

Figure \(9.47\) shows how the magnetic properties of a compound can be measured experimentally. When such measurements are made, the sample is generally covered by an atmosphere of pure nitrogen gas rather than air. Why do you suppose this is done?

Short answer

An atmosphere of pure nitrogen gas is used in experimental measurements of magnetic properties to reduce the interference of oxygen, a paramagnetic element present in air. Nitrogen, being a diamagnetic element, has little to no effect on the magnetic properties of a sample when placed in an external magnetic field. Using pure nitrogen gas creates a stable environment for accurate measurement and eliminates the influence of air's paramagnetic component (oxygen) on the magnetic properties of the sample.

Step-by-step solution

Understand the composition of air

Before we discuss why nitrogen is used, let's first understand the composition of air. Air is a mixture of different gases, which mainly consist of nitrogen (about 78%), oxygen (21%), and other trace gases like carbon dioxide and argon. The key here is to consider the properties of these major components (nitrogen and oxygen) and how they could affect the magnetic properties of a sample.

Discuss the magnetic properties of nitrogen and oxygen

Nitrogen is a diamagnetic element, meaning it creates an induced magnetic field in the opposite direction of an external magnetic field. As a result, diamagnetic materials have little to no effect on the magnetic properties of a sample when placed in an external magnetic field. On the other hand, oxygen is a paramagnetic element, which means its electrons are not all paired up, and as a result, it creates a magnetic field when exposed to an external magnetic field. Therefore, it can alter the magnetic properties of a sample if it is present during a magnetic measurement.

Explain why nitrogen is used over air

To obtain accurate results in measuring the magnetic properties of a compound, it's important to ensure that the surrounding environment does not interfere with these measurements. Since nitrogen is diamagnetic and does not affect the magnetic properties of the sample, using an atmosphere of pure nitrogen gas would create a stable environment for accurate measurement. This eliminates the influence of air's paramagnetic component (oxygen) on the magnetic properties of the sample. In conclusion, an atmosphere of pure nitrogen gas is used in experimental measurements of magnetic properties to reduce the interference of oxygen (a paramagnetic element) and improve the accuracy of the measurements.

Key concepts

Diamagnetic Materials

Diamagnetic materials, such as nitrogen, copper, and water, display unique magnetic interactions when subjected to an external magnetic field. Unlike their magnetic counterparts, diamagnetic substances do not have innate magnetic properties. Instead, they produce an induced magnetic field in a direction opposite to the applied external field. How does this occur? It's due to the electron configuration within these materials.

Each electron in an atom creates its own tiny magnetic field. In diamagnets, all the electrons are paired, and the fields they create cancel each other out, resulting in no net magnetic field. When an external magnetic field is applied, it causes a slight shift of these paired electrons, generating an induced field that weakly opposes the external one.

The effect is so weak that diamagnetic materials get repelled by the external magnetic field, as evidenced by experiments showing water being pushed away from powerful magnets. This non-interactive behavior is precisely why diamagnetic gases, such as pure nitrogen, are used to provide a stable environment for magnetic property measurements - their presence will not distort data by introducing additional magnetic fields.

Paramagnetic Elements

In contrast to diamagnetic materials, paramagnetic elements, like oxygen, exhibit a fundamental attraction to magnetic fields. This quality arises from the presence of unpaired electrons within the atomic structure of these substances. Because unpaired electrons are magnetic dipoles, they realign in the presence of an external magnetic field, slightly strengthening it.

With this reorientation, a weak positive magnetization is produced within the substance, and hence, paramagnetic materials are attracted towards the magnetic field. Although the effect is typically feeble and only observable at low temperatures or in very intense magnetic fields, it's crucially relevant in precision measurements of a substance's magnetic properties.

Furthermore, owing to these magnetic interactions, the use of paramagnetic elements in an environment meant to measure magnetic properties can interfere with the results. This is what makes the air's oxygen content problematic in such experiments, potentially affecting the integrity of the magnetic data collected.

Composition of Air

Understanding the composition of air is essential when conducting experiments related to magnetic properties. Our atmosphere is a blend of various gases, primarily composed of nitrogen (approximately 78%) and oxygen (around 21%), with traces of other gases such as argon and carbon dioxide.

While nitrogen is generally inert and exhibits diamagnetic properties, oxygen is reactive and paramagnetic. These differences highlight the need for precise environments in research and experiments that measure magnetism. If regular air with its sizable portion of paramagnetic oxygen were used in magnetic measurements, the data could be compromised.

Therefore, selecting an appropriate atmosphere, often pure nitrogen, is a strategic choice to avoid the influence of paramagnetic elements and ensures the experimental conditions are optimal for obtaining accurate and reliable magnetic property data. This highlights the importance of environmental control in experimental settings and the rationale behind using a pure and non-interactive gas like nitrogen in such measurements.