Question

To the best of your knowledge, classify each of the following as an element, a compound, or a mixture. If it is a mixture, classify it as homogeneous or heterogeneous. a. silver coin b. air c. coffee d. soil

Short answer

a. Silver coin - Homogeneous mixture (if not pure silver). b. Air - Homogeneous mixture. c. Coffee - Homogeneous or heterogeneous mixture (depends on consistency). d. Soil - Heterogeneous mixture.

Step-by-step solution

Classify Silver Coin

A silver coin is normally made up of silver, but it can also contain other metals to make the coin harder. Therefore, if the silver coin is not pure, it is a homogeneous mixture because the different metals are evenly distributed and cannot be distinguished by eye.

Classify Air

Air is a mixture of gases, primarily nitrogen, oxygen, argon, and carbon dioxide, along with other trace gases. It is a homogeneous mixture because its composition is uniform throughout.

Classify Coffee

Coffee is a complex mixture that includes water and the various substances extracted from coffee beans. This can be either a homogeneous mixture if the coffee is well-blended and consistent, or a heterogeneous mixture if there are undissolved coffee grounds or sediments.

Classify Soil

Soil consists of particles of different sizes and types, such as sand, silt, clay, organic matter, and various microorganisms. It is a heterogeneous mixture because the components are not uniform throughout, and the individual parts can be seen and separated physically.

Key concepts

Elements vs Compounds vs Mixtures

Understanding the classification of matter is foundational in chemistry and helps in grasping how substances interact with each other.

Elements are pure substances that consist of a single type of atom, like oxygen or gold. Compounds are made up of two or more elements chemically combined in a fixed proportion, such as water (H2O) or carbon dioxide (CO2). Whereas Mixtures consist of two or more substances that are physically blended but not chemically bonded, and their composition can be variable.

Taking a silver coin as an example, while one may think it's an element, it is usually a mixture because it contains other metals to increase its durability. Specifically, it's a homogenous mixture where the different metals are evenly distributed and indistinguishable to the naked eye.

Homogeneous Mixtures

When a mixture has a consistent composition throughout, it’s termed a homogeneous mixture. These mixtures are uniform in appearance and composition because the constituent parts are mixed at the molecular level. Air is a classic example, composed of various gases like nitrogen and oxygen that are evenly distributed. Another everyday homogeneous mixture is coffee, assuming it is well-blended without any sediment.

Characteristics of Homogeneous Mixtures

• Their composition is uniform.
• The components are not visually distinguishable.
• They can be composed of solids, liquids, or gases.

This uniformity in composition means you can take any sample from a homogeneous mixture, and it will have the same properties and ratio of substances as any other sample from the same mixture.

Heterogeneous Mixtures

In contrast to homogeneous mixtures, heterogeneous mixtures have a non-uniform composition. Ingredients in these mixtures are not evenly distributed, and they are visually distinct and separable. Soil is an ideal example as it comprises various components, such as sand, clay, and organic matter, which can be identified and separated by their physical properties.

Characteristics of Heterogeneous Mixtures

• Their composition varies from one part of the mixture to another.
• Constituent substances are visually distinguishable and separable.
• The components can exist in more than one phase (solid, liquid, or gas).

An interesting feature of heterogeneous mixtures is their variability; two samples from a heterogeneous mixture could have completely different properties, which is why soil from one location may differ significantly in composition and characteristics from another.