Question

Classify each of the following as a(n) element, compound, pure substance, homogeneous mixture, and/or heterogeneous mixture. More than one classification is possible, and not all of them may be used. a. calcium carbonate \(\left(\mathrm{CaCO}_{3}\right)\) b. iron c. water you regularly drink (from your faucet or a bottle)

Short answer

a. Calcium Carbonate (\(\mathrm{CaCO}_{3}\)): compound, pure substance b. Iron: element, pure substance c. Water you regularly drink (from your faucet or a bottle): homogeneous mixture

Step-by-step solution

Identify the type of substance

Calcium carbonate is a chemical compound consisting of calcium, carbon, and oxygen atoms in a fixed proportion (1:1:3).

Classify Calcium Carbonate

As a compound, calcium carbonate is a pure substance (uniform composition) made from chemically combined elements. Thus, calcium carbonate is classified as a compound and a pure substance. b. Iron

Identify the type of substance

Iron is an element represented by the symbol 'Fe' in the periodic table, and cannot be separated into simpler substances by chemical means.

Classify Iron

As an element, iron is a pure substance with a uniform composition. Thus, iron is classified as an element and a pure substance. c. Water you regularly drink (from your faucet or a bottle)

Identify the type of substance

Regular drinking water (from a faucet or bottle) is not just composed of H\(_{2}\)O molecules, but also contains dissolved minerals, ions, and possibly other impurities, making it a mixture of various substances.

Classify Drinking Water

Since the composition is uniform at the macroscopic level, with no distinct visible phases, drinking water is considered a homogeneous mixture.

Key concepts

Elements and Compounds

Elements and compounds are fundamental types of pure substances. An element is defined as a pure substance consisting of only one type of atom. Each element is unique with a specific number of protons in its atomic structure, and there are currently 118 recognized elements in the periodic table. Examples include oxygen (O), carbon (C), and iron (Fe). Iron is specifically mentioned in the exercise, and it highlights the point that elements cannot be further broken down by chemical reactions because they are already in their simplest form.
On the other hand, compounds are pure substances formed by chemically binding two or more elements in fixed proportions. These elements are bonded together through chemical bonds, which means compounds have distinct chemical properties different from their constituent elements. A great example from the exercise is calcium carbonate (CaCO extsubscript{3}), which is composed of calcium, carbon, and oxygen. Despite its three-element composition, it behaves as a single substance with unique properties that do not resemble those of pure calcium, pure carbon, or pure oxygen alone.
Both elements and compounds are integral in studying chemistry because they represent the building blocks of all matter. They rely on chemical equations to express the compositions and reactions they undergo.

Pure Substances

Pure substances are materials composed of only one type of particle. This could be a single type of element or a single type of compound. Pure substances have uniform and definite compositions, which means you won't find any variations in concentration, regardless of which part of the substance you examine. This consistency also translates to consistent physical properties, such as boiling point and melting point.
Take iron from the exercise as an example; it's an element and thus a pure substance. Similarly, calcium carbonate is a compound and also qualifies as a pure substance because its chemical composition is consistent throughout. Since it contains only the atoms of calcium, carbon, and oxygen in fixed ratios, calcium carbonate exemplifies a compound with a uniform structure.
Pure substances often have unique properties that can be used to identify them. For instance, the density of pure iron or the solid form of calcium carbonate can be used to recognize these substances. It’s an important concept not only in chemistry but also in various applied sciences and industries, such as identifying the purity of metals or compounding chemicals for specific purposes.

Homogeneous and Heterogeneous Mixtures

Mixtures consist of two or more substances that are physically combined, as opposed to chemically bonded. They can be classified into two broad categories: homogeneous and heterogeneous mixtures.
Homogeneous mixtures, or solutions, are uniform throughout. This means that the different components are evenly distributed, and no distinct layers or parts are visible. Drinking water from the exercise fits this description perfectly. Despite containing various dissolved minerals and impurities, these are blended so well at the macroscopic level that they appear uniform to the naked eye. An everyday example is sugar dissolved in water, where the sugar is uniformly distributed within the liquid.

• Characteristics: Single phase, uniform appearance, consistent properties through any sample.
• Examples: Air, saltwater, and most beverages like the mentioned drinking water.

On the opposite end are heterogeneous mixtures, where the different components are not uniformly mixed, and distinct phases can often be seen. These might not have been highlighted in the exercise, but examples include sand in water or salads, where each constituent retains its physical properties and structure.

• Characteristics: Multiple phases, visibly different parts, non-uniform composition.
• Examples: Sand and iron filings, oil and vinegar, various forms of trail mix.

Understanding these differences helps in fields like material science, chemistry, and environmental science, where the separation of mixtures becomes crucial in both analytical and practical applications.