Question

Classify each of these as an element, a compound, a heterogeneous mixture, or a homogeneous mixture. Explain your choice in each case. (a) Chunky peanut butter (b) Distilled water (c) Platinum (d) Air

Short answer

(a) Heterogeneous mixture; (b) Compound; (c) Element; (d) Homogeneous mixture.

Step-by-step solution

Classify Chunky Peanut Butter

Chunky peanut butter is classified as a **heterogeneous mixture**. This is because it contains visibly different components like chunks of peanuts and the smooth peanut paste, which means the composition is not uniform throughout.

Classify Distilled Water

Distilled water is classified as a **compound**. It consists of only water molecules (H₂O) and has a uniform composition, making it a pure substance. Distillation removes impurities, ensuring all samples contain exactly the same particles.

Classify Platinum

Platinum is classified as an **element**. It is a pure chemical substance consisting of a single type of atom, listed on the periodic table with the symbol Pt.

Classify Air

Air is classified as a **homogeneous mixture**. It consists of different gases such as nitrogen, oxygen, carbon dioxide, and argon mixed so thoroughly that they appear uniform throughout.

Key concepts

Element

Elements are the simplest form of matter, comprising only one type of atom. They are pure substances that cannot be broken down into simpler substances by chemical means. Elements are the building blocks of all matter and are represented in the periodic table. Each element is assigned a unique chemical symbol, like Pt for platinum. This particular classification is vital because elements serve as the foundation for compounds and mixtures.
For example, platinum is a dense, malleable, highly unreactive precious metal. In scientific studies, it is often used as a catalyst and in various industrial applications. Since it consists entirely of platinum atoms, it remains unaltered by chemical reactions unless combined with other elements to form compounds.

Compound

Compounds are pure substances formed when two or more elements chemically bond in fixed proportions. Unlike mixtures, the composition of a compound is uniform throughout, meaning each part of the compound is identical at the molecular level. This uniformity is what distinguishes compounds from mixtures.
An example of a compound is distilled water, consisting of two hydrogen atoms bonded to one oxygen atom ( H_2O ). Despite potential impurities found in regular water, the distillation process removes these impurities, leaving a pure chemical substance. Thus, each molecule of distilled water is identical, giving it a consistent composition and set of physical properties.

Heterogeneous Mixture

A heterogeneous mixture is a combination of substances in which the components are not evenly distributed. This means that different samples demonstrate varied composition and properties. In simple terms, you can often identify or separate the different parts of a heterogeneous mixture. These mixtures can involve solids, liquids, or gases.
For example, chunky peanut butter is a well-known heterogeneous mixture. It contains visible chunks of peanuts dispersed within a smooth paste, resulting in an inconsistent texture and appearance. The physical characteristics of the chunks and the paste differ, which is why they are not uniformly combined.

Homogeneous Mixture

Homogeneous mixtures, also known as solutions, have uniform composition and properties throughout. The individual components cannot be distinguished as they are thoroughly mixed at the molecular level. These mixtures are formed when two or more substances are combined in such a way that they appear as a single phase.
Air serves as a classic example of a homogeneous mixture. It is composed of various gases like nitrogen, oxygen, carbon dioxide, and argon, which are so well mixed that air appears uniform no matter where you sample it. This thorough mixing allows air to maintain consistent properties across different locations, making it a great example of a homogeneous mixture.