Question

Classify each substance as a pure substance or a mixture. If is a pure substance, classify it as an clement or a compound. If it is a mixture, classify it as homogeneous or heterogeneous. \begin{equation} \begin{array}{ll}{\text { a. }} & {\text { b. beef stew }} \\ {\text { c. iron }} & {\text { d. carbon monoxide }}\end{array} \end{equation}

Short answer

Beef stew is a heterogeneous mixture; iron is a pure substance and an element; carbon monoxide is a pure substance and a compound.

Step-by-step solution

Classifying Beef Stew

Firstly, consider beef stew. Beef stew consists of various ingredients such as meat, vegetables, and broth that are physically combined. Therefore, it is not a pure substance due to its combination of different components. Since you can see and distinguish the different ingredients in beef stew, and its composition is not uniform throughout, it is classified as a heterogeneous mixture.

Classifying Iron

Next, look at iron. Iron is an element found on the periodic table and consists of only one kind of atom, Fe. Since it is not made up of different substances and is made up of identical atoms, it is considered a pure substance. More specifically, since it is a single type of atom, it is classified as an element.

Classifying Carbon Monoxide

Now, examine carbon monoxide. Carbon monoxide has a chemical formula CO, indicating it is composed of carbon (C) and oxygen (O) atoms chemically combined in a 1:1 ratio. As such, it is not a mixture but a pure substance. Since it contains more than one type of atom joined together, it is classified as a compound.

Key concepts

Heterogeneous Mixtures

When we talk about heterogeneous mixtures, we refer to combinations of substances that are not uniform throughout. Take beef stew as an illustrative example. It’s a classic illustration of a heterogeneous mixture because it contains chunks of meat, diced vegetables, and various herbs and spices, all in a broth. These components maintain their distinct identities and can be easily separated due to the visible differences in texture, color, and phase within the mixture.

Pizza with toppings, a pile of different coins, and even a sample of soil with pebbles, sand, and organic matter are all everyday examples of heterogeneous mixtures. In the classroom setting, this concept helps students understand that not all mixtures are the same, and the uneven distribution of components is a key characteristic of heterogeneity.

Element Classification

The term 'element' is foundational in chemistry, designating substances that are composed of only one kind of atom. Iron, for instance, is an element frequently discussed in educational settings because its atomic structure is purely made of iron atoms (Fe). Elements are listed on the Periodic Table, which acts as a sort of 'directory' of the elements, providing important information about their properties and how they react with other elements.

Elements are classified into metals, nonmetals, and metalloids based on their properties. Examples of each include gold (Au) as a metal, oxygen (O) as a nonmetal, and silicon (Si) as a metalloid. This classification helps scientists and students alike understand elements' potential for forming compounds and their behavior under different conditions.

Compound Classification

We categorize compounds as pure substances that are formed from the chemical combination of two or more different types of atoms. A classic example is carbon monoxide (CO), which is a toxic, colorless gas made from one carbon atom and one oxygen atom bonded together. Compounds have unique properties that are distinct from the elements they are made of, which is why they are an essential concept in chemistry.

Water (H₂O), table salt (NaCl), and sugar (C₁₂H₂₂O₁₁) are all compounds. Understanding compounds requires a grasp of chemical formulas, the fixed ratios of the constituent atoms, and their precise arrangement in molecular structure. Studying compounds empowers students to predict the properties, reactivity, and applications of various substances.