Problem 25 - General Chemistry

Question

A. Sodium metal is partially melted. What are the two phases present? B. A sample of sand is composed of granules of quartz (silicon dioxide) and seashells (calcium carbonate). The sand is mixed with water. What phases are present?

Step-by-Step Solution

Answer

A. Solid and liquid sodium; B. Solid quartz, solid calcium carbonate, liquid water.

Step 1: Identifying Phases in Partially Melted Sodium

When sodium metal is partially melted, it means that some of the solid sodium has transformed into a liquid while the rest remains solid. Therefore, the two phases present are the solid phase and the liquid phase of sodium.

Step 2: Understanding Sand Composition

Sand is composed of quartz (silicon dioxide) and seashells (calcium carbonate). These components do not dissolve significantly in water, but their phases remain distinct because they typically do not react with water under normal conditions.

Step 3: Identifying Phases in the Sand-Water Mixture

In a mixture of sand and water, the phases include the solid phase of quartz, the solid phase of calcium carbonate, and the liquid phase of water. Although mixed, they exist as distinct phases because they do not chemically combine or dissolve to a significant extent.

Key Concepts

Sodium Metal

Sodium metal is a fascinating and reactive alkali metal known for its shiny appearance and soft texture. At room temperature, it exists as a solid. However, it has an exceptionally low melting point of 97.8°C (207.6°F), meaning it can easily transition from solid to liquid. When sodium metal is partially melted, both solid and liquid phases can coexist.

• Solid Phase: This represents atoms arranged in a structured, rigid manner.
• Liquid Phase: Here, atoms are less ordered and free to move past each other, resulting in a fluid state.

Understanding these phases is crucial because sodium's behavior can drastically vary with temperature. Being highly reactive, sodium's liquid phase is especially susceptible to rapid oxidation when exposed to air or moisture.

Solid-Liquid Equilibrium

Solid-liquid equilibrium is a fascinating concept that happens when two phases, solid and liquid, stay in balance. This occurs as they continuously exchange particles while maintaining constant temperature and pressure.

Imagine melting sodium metal as it approaches its melting point. You will have both solid and liquid sodium in equilibrium.

• In this state, the amount of solid and liquid is stable.
• No net melting or freezing occurs within this balance.
• Maintaining equilibrium depends on not changing temperature or pressure.

Recognizing solid-liquid equilibrium allows us to predict and control phase behavior in chemical and physical processes.

Sand-Water Mixture

When sand is mixed with water, this creates a mixture with distinct phases. Sand can be composed of materials like quartz and seashells which do not dissolve in water. The mixture retains separate phases because these substances do not chemically interact with water.

• Quartz (Silicon Dioxide): This remains as solid particles suspended in water.
• Calcium Carbonate: Like quartz, this also stays as a solid phase.
• Water: Acts as the liquid phase surrounding the solid particles.

Such a mixture is not a chemical reaction but rather a physical combination where each component retains its original properties.

Component Phases

Component phases refer to the different states of matter present in a mixture. Each has unique characteristics and interactions. In the case of a sand-water mixture, distinguishing between the different component phases is essential.

• Solid Phases: Multiple solid components, such as quartz and calcium carbonate, existing distinctly within the liquid.
• Liquid Phase: The medium which holds or suspends the solid components, usually water in such mixtures.

Understanding the concept of component phases aids in identifying how different materials interact and retain their properties when combined. It provides insights into separations and filtering methods in both natural and laboratory settings.