Problem 85 - Chemistry Matter and Change

Question

Classify each substance as a pure substance, a homogeneous mixture, or a heterogeneous mixture. \begin{equation} \begin{array}{llll}{\text { a. air }} & {\text { c. soil }} & {\text { e. sediment }} \\ {\text { b. aerosol }} & {\text { d. water }} & {\text { f. muddy water }}\end{array} \end{equation}

Step-by-Step Solution

Answer

Air - homogeneous mixture; Aerosol - heterogeneous mixture; Soil - heterogeneous mixture; Water - pure substance; Sediment - heterogeneous mixture; Muddy water - heterogeneous mixture.

Step 1: Understanding Pure Substances

A pure substance is a material with a consistent composition and distinct chemical properties. It's made of one type of particle or molecule throughout.

Step 2: Understanding Homogeneous Mixtures

A homogeneous mixture is a combination of substances where the components are uniformly distributed, and the mixture appears as a single phase or uniform texture.

Step 3: Understanding Heterogeneous Mixtures

A heterogeneous mixture consists of visibly different substances or phases. The components are not uniformly distributed, and you can often distinguish individual parts.

Step 4: Classifying Air

Air is primarily a mixture of gases (like nitrogen and oxygen) evenly mixed throughout, showing uniform properties. Therefore, it is a homogeneous mixture.

Step 5: Classifying Aerosol

An aerosol contains particles dispersed within a gas. Since the particles can be distinguished from the surrounding gas, it's considered a heterogeneous mixture.

Step 6: Classifying Soil

Soil is composed of various components like minerals, organic material, and moisture that are not evenly distributed. This makes soil a heterogeneous mixture.

Step 7: Classifying Water

Water, in its pure form (H2O), consists of just one type of molecule. Therefore, pure water is a pure substance.

Step 8: Classifying Sediment

Sediment is usually composed of particles that have settled out of a liquid. It has distinguishable parts, making it a heterogeneous mixture.

Step 9: Classifying Muddy Water

Muddy water contains suspended particles along with water. The presence of these non-uniformly distributed particles makes it a heterogeneous mixture.

Key Concepts

Pure Substances

A pure substance is a type of matter that maintains a consistent composition and distinct set of properties. These substances are comprised of only one type of particle throughout their entire structure. For instance, pure water, known chemically as \(H_2O\), consists solely of water molecules with no other substances mixed in. Pure substances can be further divided into elements and compounds:

• **Elements**: These are the simplest pure substances and consist of only one type of atom. Examples include gold (Au) and oxygen (\(O_2\)).
• **Compounds**: These consist of two or more elements chemically combined in a fixed ratio. For example, sodium chloride (\(NaCl\)) is a compound made from sodium and chlorine.

Understanding pure substances is crucial as they form the fundamental building blocks of chemistry. Each element and compound has specific chemical and physical properties that can be distinctly identified.

Homogeneous Mixtures

Homogeneous mixtures are combinations where the different components are evenly distributed throughout the mixture. This results in a single-phase appearance, meaning you can't see individual substances within the mixture. An excellent everyday example of a homogeneous mixture is the air we breathe. It is made up mostly of nitrogen and oxygen gases, but these are spread uniformly, giving air an even composition.
Homogeneous mixtures can involve:

• **Solutions**: These are homogeneous mixtures where one substance is completely dissolved in another, such as sugar in water.
• **Alloys**: These are solid solutions like brass, which is an alloy of copper and zinc.

The uniformity of homogeneous mixtures makes them different from heterogeneous mixtures, where the components are not uniformly distributed. Recognizing this type of mixture is a key skill in both science and everyday life.

Heterogeneous Mixtures

A heterogeneous mixture is one in which the different components are not uniformly distributed, and the individual substances remain distinct. This means that you can often see the separate components with the naked eye or with a simple magnification tool. For example, soil is a prime example of this type of mixture. It contains minerals, organic matter, and moisture in visible clumps or parts.
Other examples of heterogeneous mixtures include:

• **Salad**: A mixture of various vegetables where the different ingredients remain separate.
• **Granite**: A type of rock composed of different minerals like quartz, mica, and feldspar that are visibly distinct.

Identifying a heterogeneous mixture involves looking for variations in composition, which is a vital part of understanding material classification in both natural and manufactured products.