Question

Classify each substance as a pure substance or a mixture. If it is a pure substance, classify it as an element or a compound. If is a mixture, classify it as homogeneous or heterogeneous. \begin{equation} \begin{array}{ll}{\text { a. sweat }} & {\text { b. carbon dioxide }} \\\ {\text { c. aluminum }} & {\text { d. vegetable soup }}\end{array} \end{equation}

Short answer

a. Homogeneous mixture, b. Compound, c. Element, d. Heterogeneous mixture.

Step-by-step solution

- Classify sweat

Sweat is a mixture of water, salts, and other substances. It has uniform composition throughout, which makes it a homogeneous mixture.

- Classify carbon dioxide

Carbon dioxide is composed of carbon and oxygen chemically combined in a fixed ratio. It is a pure substance, and more specifically, it is a compound.

- Classify aluminum

Aluminum is an element. It is a pure substance made up of only one kind of atom and cannot be broken down into simpler substances by chemical means.

- Classify vegetable soup

Vegetable soup is a mixture of various ingredients that do not have a uniform composition. It can contain vegetables, liquids, and other substances, making it a heterogeneous mixture.

Key concepts

Pure Substance and Mixture

Understanding the differences between pure substances and mixtures is fundamental in the study of chemistry. A pure substance is a form of matter that has a constant composition and properties that are constant throughout the sample. It can exist in two forms: elements and compounds. An element is a pure substance that cannot be broken down into simpler substances by chemical means. It consists of one type of atom, such as aluminum (Al), which is used in various industries for its lightweight and durability.

On the other hand, a compound is a pure substance composed of two or more different elements that are chemically bonded together in a fixed ratio. An example of this is carbon dioxide (CO2), a gas essential to the photosynthesis process in plants. Mixtures, unlike pure substances, consist of two or more substances that are physically combined. These substances in a mixture retain their individual chemical properties. A mixture can be further classified into homogeneous and heterogeneous mixtures based on the uniformity of their composition. Sweat, as an example, is a homogeneous mixture because its composition of water, salts, and other substances is uniform throughout.

Element versus Compound

The distinction between an element and a compound is crucial for students to grasp. An element is composed of only one kind of atom, which is the smallest unit of an element that maintains the chemical properties of that element. Elements can be found on the periodic table; for instance, aluminum (Al) is the 13th element on the table known for its metallic properties.

A compound, however, involves a chemical combination of two or more different elements bonded together. Water (H2O), for example, is a compound formed from hydrogen and oxygen atoms in a 2:1 ratio. Compounds have properties that are different from those of the individual elements that comprise them. They can be broken down into their constituent elements through chemical reactions, something that is not possible with elements, which are substances in their simplest form.

Homogeneous and Heterogeneous Mixtures

When it comes to mixtures, understanding the difference between homogeneous and heterogeneous types is important for identifying materials in daily life. A homogeneous mixture has a uniform composition and appears the same throughout. Solutions, like sweat or saltwater, are common examples where the dissolved material is not visibly distinguishable from the solvent. This type of mixture is also called a solution.

In contrast, a heterogeneous mixture consists of visibly different substances or phases. The components in a heterogeneous mixture are not uniformly spread out. An example of this is vegetable soup, which has pieces of vegetables, grains, and broth that can be seen and separated from one another. Heterogeneous mixtures can be as simple as a mixture of sand and water or as complex as a bowl of salad with various vegetables, fruits, and dressings mixed together.