Question

The soldiers of Napolean's army, while on Alps during freezing winter, suffered a serious problem as regards to the tin buttons of their uniforms. White metallic tin buttons got converted to grey powder. This transformation is related to (a) an interaction with nitrogen of the air at very low temperatures (b) a change in the crystalline structure of tin (c) an interaction with water vapour contained in the humid air (d) a change in the partial pressure of oxygen in the air.

Short answer

The transformation is related to (b) a change in the crystalline structure of tin.

Step-by-step solution

Identify the Problem

The problem states that the white metallic tin buttons transformed into grey powder during the cold winters in the Alps. We need to determine the cause of this transformation from the given options.

Understand Tin Transformation

At low temperatures, especially below 13.2°C, tin undergoes a transition from its metallic form (white tin or beta-tin) to its non-metallic form (grey tin or alpha-tin). This change is a structural transition where the crystalline structure of the tin is altered.

Evaluate the Options

Option (a) mentions an interaction with nitrogen, which doesn't specifically affect tin's structure at low temperatures. Option (c) mentions water vapor, but there is no chemical reaction leading to a powdery form in this case. Option (d) cites oxygen's partial pressure, which doesn't impact the structural form here. Option (b) refers to a change in crystalline structure, matching the known transition of tin to grey powder at low temperatures.

Select the Correct Explanation

Based on the understanding that tin undergoes a structural change at cold temperatures (from beta-tin to alpha-tin), option (b) which mentions a change in the crystalline structure of tin is the correct explanation for the problem experienced by Napoleon's soldiers.

Key concepts

Crystalline structure change

Tin, like many elements, possesses different forms known as allotropes. These allotropes differ in their crystalline structure, which refers to how atoms are arranged in a solid. The structure directly influences its properties and appearance. When environmental conditions change, particularly temperature, these structures can shift, leading to significant changes in the material.
For tin, the transition involves moving between two distinct crystalline forms. The metal can exist as metallic white tin, which is a body-centered tetragonal structure, or as non-metallic grey tin with a diamond cubic structure. This metal transitions between these forms when subjected to different temperature conditions.
Therefore, the change in crystalline structure is fundamental to understanding the behavior of materials under varying environmental conditions.

Beta-tin to alpha-tin transition

When the temperature drops below 13.2°C, tin undergoes a transition from beta-tin to alpha-tin. Beta-tin, or white tin, is shiny and metallic. It is the form that is more stable at higher temperatures. During winter, such as the harsh freezing conditions experienced by Napolean's army in the Alps, tin buttons began transitioning to alpha-tin.
Alpha-tin, also known as grey tin, appears as a dull grey powder and is non-metallic. This process is commonly referred to as "tin pest" or "tin disease" and is a perfect example of an allotropic transformation attributed to a change in crystalline structure. This phenomenon keeps illustrating how minute variations in temperature can transform a solid's physical state.

• Beta-tin is stable above 13.2°C and has a metallic luster.
• Alpha-tin becomes stable below 13.2°C, leading to a brittle and powdery form.

Effect of low temperature on tin

Temperature plays a critical role in the chemical and physical forms of tin. Low temperatures catalyze the shift from beta-tin (metallic) to alpha-tin (powdery non-metallic). This transition was notably observed by Napoleon's soldiers when their tin uniform buttons turned to powder during their campaign in the frigid climate of the Alps.
This transformation emphasizes how cold temperatures can influence metal stability, by changing the crystallinity of the material. Such environmental effects on materials must be considered in applications where structural integrity is crucial under variable temperatures. In regions where temperatures can frequently dip below 13.2°C, alternate materials or protective measures for tin must be considered to avoid degradation.

• Low temperatures can trigger transformations in metals, impacting their utility.
• For tin, this transformation changes it from a sturdy metal to a fragile powder.