Question

Which of the following describes a chemical property? a. The density of iron is 7.87 \(\mathrm{g} / \mathrm{cm}^{3} .\) b. A platinum wire glows red when heated. c. An iron bar rusts. d. Aluminum is a silver-colored metal.

Short answer

The statement that describes a chemical property is "An iron bar rusts" (option c), as it involves a chemical change and the formation of a new substance.

Step-by-step solution

Analyze option a.

The density of iron is given as 7.87 g/cm³. Density is a physical property because it can be measured without any chemical change occurring. Hence, option a is not a chemical property.

Analyze option b.

A platinum wire glows red when heated. This statement describes a physical change that occurs as a result of heat. There is no new substance formed in the process, so it is a physical property and not a chemical property. Option b is also not a chemical property.

Analyze option c.

An iron bar rusts. Rusting is a process that involves a chemical reaction between iron and oxygen in the presence of moisture, forming a new substance called iron oxide or rust. This statement describes a chemical change as it involves the formation of a new substance. Hence, option c is a chemical property.

Analyze option d.

Aluminum is a silver-colored metal. Color is a characteristic that can be observed without undergoing any chemical change. Therefore, color is a physical property, not a chemical property. Option d is not a chemical property.

Final answer.

Based on the analysis in the previous steps, the statement that describes a chemical property is "An iron bar rusts" (option c).

Key concepts

Physical Properties

Physical properties are characteristics of a substance that can be observed or measured without changing the substance's chemical identity. These properties include:

• Density: This is the mass per unit volume of a substance, such as iron's density of 7.87 g/cm³.
• Color: The appearance or hue of a substance. For example, aluminum is known for its silver color.
• Melting point: The temperature at which a substance turns from solid to liquid, observable without a chemical change.
• Boiling point: The temperature at which a solid turns into a gas.

These properties are crucial because they help identify and classify substances without altering their basic nature.
Recognizing physical properties is essential for scientific research and real-world applications, like selecting materials for construction or engineering purposes.

Chemical Change

A chemical change involves a substance transforming into one or more new substances. These changes occur due to chemical reactions, where the original substances (reactants) interact to form new ones (products).
Indicators of a chemical change include:

• Formation of a new substance: This is the most telling sign, as seen when iron turns into rust.
• Change in temperature: Chemical reactions often release or absorb heat.
• Emission of gas: Bubbles or fumes appearing can indicate a chemical change.
• Formation of a precipitate: A solid that forms from a solution during a chemical reaction.

Chemical changes are integral to many processes in nature and industry, from digestion to metallurgy.

Rusting

Rusting is a specific type of chemical change where iron reacts with oxygen and moisture to form iron oxide, commonly known as rust. This process is both a chemical reaction and a chemical property of iron.
The rusting process involves:

• Iron reacting with oxygen in the presence of water or moisture.
• Formation of a new compound: Iron oxide, which has different properties from metallic iron.
• Energy release: Often perceived as a slight warmth during significant amounts of rusting.

Preventing rust involves coating iron with protective layers, like paint, or using rust-resistant alloys. Understanding rusting is vital for maintaining infrastructure and vehicles.

Chemical Reaction

A chemical reaction is a process where substances interact to form new substances. These reactions are fundamental to both chemistry and biology.
Key aspects of chemical reactions include:

• Reactants and products: Original substances are transformed into new ones. For example, iron and oxygen are reactants in the rusting process, and iron oxide is the product.
• Energy changes: Reactions can release (exothermic) or absorb (endothermic) energy.
• Reaction rate: How fast a reaction proceeds can depend on temperature, concentration, and catalysts.
• Reversibility: Some reactions can be reversed, but others, like rusting, usually cannot without additional energy or alteration.

Understanding chemical reactions is crucial for designing chemical processes, from manufacturing to pharmaceuticals.