Question

The soldiers of Napolean army while at 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 power. This transformation is related to: (a) A change in the partial pressure of oxygen in the air (b) An interaction with water vapour contained in the humid air. (c) A change in the crystalline structure of tin. (d) An interaction with nitrogen of the air at very low temperatures.

Short answer

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

Step-by-step solution

Understand the Problem

The problem describes the transformation of tin buttons from a metallic state to a powdery form when exposed to freezing winter conditions in the Alps. You need to identify the cause of this transformation from the given options.

Analyze the Options

Read the options carefully to see how they relate to the properties and transformation of tin: - Option (a) involves oxygen, which is not directly related to tin's transformation. - Option (b) mentions interaction with water vapor, which could influence oxidation but not this specific change. - Option (c) involves a change in crystalline structure, which is significant in transformations under temperature changes. - Option (d) involves nitrogen, which does not chemically affect tin.

Recall Basic Chemistry of Tin

At low temperatures, such as those in the Alps during winter, tin undergoes allotropy, changing from the white, metallic β-tin to grey, powdery α-tin. This is known as 'tin pest' or 'tin disease' and is a change in crystalline structure that happens under cold conditions.

Evaluate and Select the Correct Option

Since the transformation of tin is due to a change in its crystalline structure at low temperatures, option (c) addresses this directly. This phenomenon is not due to water vapor interaction, oxygen partial pressure, or nitrogen presence, making option (c) the correct choice.

Key concepts

Crystalline Structure

Crystalline structure refers to the organized, repeating arrangement of atoms in a solid. In the case of metals like tin, the crystalline structure defines many of its physical properties. Tin has two key crystalline forms, or allotropes: \( \beta \)-tin and \( \alpha \)-tin. At room temperature, tin normally exists as \( \beta \)-tin, which is a silvery, metallic form. This structure is robust and stable under normal conditions. However, at temperatures below \( 13.2°C \), tin begins to transform into \( \alpha \)-tin, a non-metallic, grey powdery form. This transformation changes the arrangement of atoms, affecting the characteristics of the metal.

• \( \beta \)-tin is metallic and stable at higher temperatures.
• \( \alpha \)-tin is less dense and exists at lower temperatures.

This transformation of the crystalline structure underlies the severe issue known as 'tin pest' or 'tin disease.' Understanding the conditions that cause changes in crystalline structure helps explain why Napoleon's army faced issues with tin buttons in cold climates.

Tin Pest

'Tin pest' is a term used to describe the deterioration of tin due to its phase transformation at low temperatures. When temperatures drop below \( 13.2°C \), \( \beta \)-tin transforms into \( \alpha \)-tin. This transformation isn't just a cosmetic change; it results in a complete structural breakdown from a solid metal into a crumbly powder.

• Tin pest occurs in cold conditions, often below freezing, such as in the Alps.
• This is a slow process but ultimately renders the material unusable.

The problem was notably documented during Napoleon’s campaign, where soldiers' tin buttons crumbled in the cold weather. This phenomenon is a fascinating example of how environmental conditions impact material stability.

Phase Transformation

Phase transformation refers to the change of a substance from one phase to another due to external conditions like temperature or pressure. In tin, phase transformation is particularly relevant due to the dramatic shift between its two allotropes: \( \beta \)-tin and \( \alpha \)-tin.

The phase transformation from the high-temperature metallic state to the low-temperature non-metallic state involves reorganization of the atoms. It's driven by changes in thermodynamic stability at lower temperatures. This means that what is stable at room temperature becomes unstable and converts into another phase as the temperature falls.

• The conversion can cause structural and mechanical failures, which can be disastrous without proper materials science knowledge.
• Understanding these transformations is critical for materials used in challenging environments.

This principle is crucial for engineers and scientists when choosing materials for use in different climate conditions.