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 correct answer is option \(c\): An iron bar rusts, which involves a chemical reaction as the iron reacts with oxygen and moisture, altering its chemical composition.

Step-by-step solution

Understanding the Options

Firstly, let's go through each of the options and comprehend their nature as a property: a. The density of iron is 7.87 g/cm³ - This is a physical property as it can be observed without a chemical reaction taking place. Density represents mass per unit volume. b. A platinum wire glows red when heated - This is a physical property since the glowing red wire doesn't involve a chemical reaction or change in the composition of platinum. c. An iron bar rusts - This involves a chemical reaction as the iron reacts with oxygen and moisture to form rust. This process alters the chemical composition of the iron. d. Aluminum is a silver-colored metal - This is a physical property, expressing the color and appearance of aluminum without involving any chemical reaction or alteration in its composition.

Identifying the Chemical Property

From the given choices, we can clearly identify that only choice 'c' involves a chemical reaction and describes how the substance interacts with other substances (oxygen and moisture): c. An iron bar rusts So, the correct answer is option \(c\).

Key concepts

Physical Properties

Physical properties are characteristics of a substance that can be observed or measured without altering the substance's chemical composition. This means you don't need a chemical reaction to see or measure them. Some common physical properties include:

• Density: This tells us how much mass is packed into a given volume. For instance, the density of iron being 7.87 g/cm³ is a clear physical property.
• Color and Appearance: Simply looking at a substance can give us insights into its physical properties. For example, aluminum being a silver-colored metal is an observational physical property.
• State of Matter: Recognizing if a substance is a solid, liquid, or gas is another basic physical property.

Density, color, and state provide valuable information without any chemical changes. This allows us to identify and study substances in their natural or undisturbed states.

Oxidation

Oxidation is a specific chemical process where a substance reacts with oxygen. This often involves the loss of electrons and results in changes to the chemical composition of the material. A common example of oxidation is rusting, where iron reacts with oxygen in the presence of moisture to form iron oxide, commonly known as rust. During this process:

• Iron goes from its pure form to iron oxide.
• There is a visible change as the iron transforms, indicating that a chemical reaction has occurred.
• The properties of iron oxide are different from the original metallic iron.

Oxidation is important in both nature and industry, affecting substances like metals and influencing processes such as corrosion. Understanding oxidation helps in fields like chemistry, engineering, and materials science.

Chemical Reactions

Chemical reactions occur when substances interact to form one or more new substances. These reactions involve changes in the chemical structure and properties of the original substances. Key points about chemical reactions include:

• Reactants and Products: The original substances in a reaction are called reactants, and the new substances formed are the products.
• Energy Change: Chemical reactions often involve changes in energy. They can be either exothermic (releasing energy) or endothermic (absorbing energy).
• Observable Changes: Indicators of a chemical reaction may include color change, heat production, gas formation, or precipitate formation.

The rusting of iron is a classic example of a chemical reaction, illustrating how iron reacts with oxygen to form a new compound—rust. Chemical reactions are fundamental to understanding how different materials interact and transform in various environments.