Problem 73 - Chemistry: Principles and Reactions

Question

Four shiny solids are labeled \(\mathrm{A}, \mathrm{B}, \mathrm{C}\), and \(\mathrm{D}\). Given the following information about the solids, deduce the identity of \(\mathrm{A}, \mathrm{B}, \mathrm{C}\), and \(\mathrm{D}\). (1) The solids are a graphite rod, a silver bar, a lump of "fool's gold" (iron sulfide), and iodine crystals. (2) \(\mathrm{B}, \mathrm{C}\), and \(\mathrm{D}\) are insoluble in water. \(\mathrm{A}\) is slightly soluble. (3) Only C can be hammered into a sheet. (4) \(\mathrm{C}\) and \(\mathrm{D}\) conduct electricity as solids; B conducts when melted; \(\mathrm{A}\) does not conduct as a solid, melted, or dissolved in water.

Step-by-Step Solution

Answer

Question: Identify the four solids (A, B, C, and D) based on their properties of solubility, ability to be hammered, and electrical conductivity. Answer: Solid A is Iodine crystals, Solid B is Iron sulfide (fool's gold), Solid C is a Silver bar, and Solid D is a Graphite rod.

Step 1: Analyze the solubility information

We know that B, C, and D are insoluble in water while A is slightly soluble. Iodine crystals are the only material slightly soluble in water among the given options. Therefore, solid A must be iodine crystals.

Step 2: Analyze the ability to be hammered into a sheet

We know that only solid C can be hammered into a sheet. The only given material that can be hammered into a sheet is silver, which is a metal. Therefore, solid C must be a silver bar.

Step 3: Analyze the electrical conductivity information

The information about electrical conductivity can help us identify B and D. We know that C and D conduct electricity as solids, and since we've already identified C as a silver bar, solid D must be graphite (as this is the only other option that conducts electricity as a solid). B conducts electricity when melted. Among the remaining options, we have "fool's gold" (iron sulfide) and graphite. Since graphite is already identified as solid D, B must be iron sulfide.

Step 4: Conclusion

Based on the given information, we can deduce the identities of the four solids as follows: - Solid A: Iodine crystals - Solid B: Iron sulfide (fool's gold) - Solid C: Silver bar - Solid D: Graphite rod

Key Concepts

Solubility in Water

When it comes to understanding chemical properties of solids, 'solubility in water' is a critical factor. Solids react with water in different ways, and this interaction determines whether a substance can be dissolved or not. In our exercise, we identified solid A as iodine crystals due to its slight solubility in water.

The solubility of a substance in water depends on the nature of the chemical bonds and the temperature of the water. For students, it's important to remember that soluble substances can create solutions, meaning they completely disseminate within the water, becoming part of the liquid phase. Insoluble substances, like solids B, C, and D (iron sulfide, silver, and graphite), do not dissolve and remain distinct from the water.

Malleability of Materials

Malleability is a property that describes a material's ability to be shaped, especially into thin sheets, without breaking. It is commonly associated with metals. In our example, only solid C is malleable enough to be hammered into a sheet, which led us to identify it as a silver bar, as silver is well known for its malleability.

Malleability is a result of metallic bonding where metal atoms can slide past each other while maintaining the cohesive strength of the material. This is a concept that often intrigues students because it's observable in everyday items like aluminum foil or gold leaf.

Electrical Conductivity

Electrical conductivity is the measure of a material's ability to conduct an electric current. In the given exercise, C and D are noted to conduct electricity as solids. This attribute is often found in metals and carbon-based materials like graphite, hence why we were able to classify solid D as graphite.

Conductivity is typically related to the presence of free electrons in a material. Metals like silver conduct electricity well because their electrons are loosely held, allowing them to move freely. Students should appreciate that this is why materials such as copper and silver are widely used in electrical wiring.

Classification of Materials

Classifying materials based on their properties, such as solubility, malleability, and electrical conductivity, helps us categorize and understand their potential applications. This exercise demonstrates how the classification of materials can be determined by observing these properties. For instance, the ability of solid C (silver bar) to be malleable classifies it as a metal, while solid D (graphite rod) is classified as a non-metal due to its electrical conductivity without being malleable.

Understanding the classification of materials is fundamental in various scientific and industrial fields. Students should grasp this concept as it helps them predict how a material may behave in different scenarios, laying the groundwork for further study in materials science.