Sand found on the beach, carbonated beverages, the Earth's atmosphere, cake mix and fog are five examples of mixtures. A mixture is a combination of substances that are not chemically bound together and are not in fixed proportions. Most substances found in nature are mixtures.
Mixtures are classified as either heterogeneous or homogeneous. The different components of heterogeneous mixtures can be distinguished visually due to different phases of matter, colors, particle sizes and other characteristics.
Beach sand is one example of a heterogeneous mixture because the various components have different sizes, shapes and colors. Carbonated beverages are also heterogeneous because the gas bubbles can be distinguished from the liquid components. Homogeneous mixtures have a uniform appearance, and the different components cannot be distinguished visually.
Many homogeneous mixtures are solutions, in which one or more components called solutes are dissolved in another component called the solvent. Salt water is a homogeneous mixture and a solution in which salt is the solute and water is the solvent. Cake mix is one example of a homogeneous mixture that is not a solution. Colloids are another type of homogeneous mixture that are not solutions; they consist of microscopic particles suspended in a solid or fluid medium. Milk and fog are both homogeneous mixtures that are colloids.