Mixtures are all around us. Remember, a mixture is anything other than a pure substance, and very few things are entirely pure substances. Walking around the house and yard, a myriad of example are instantly available. For the sake of a little organization, these examples are classified by type of mixture.
Heterogeneous Mixtures
Without any need for regularity, these mixtures might have been stirred together, crushed together, or just happened to spill into the same area. The concrete in the sidewalk is a mixture (gravel, sand, binders), and is visibly so, since much of the mixture is an agglomeration of large particles. The fertilizer pellets newly spread in the garden contain a mixture of nitrate and phosphate compounds, among other things. The paper bag it came in is a mixture of various length cellulose fibers, binders, and a bit of ink. Even the natural peanut butter turns out to be a mixture, seen easily as the oil separates over time.
Suspensions
The birds in the bird bath have stirred up the dirt in the water again. While it will clear up in time, for now the finer dirt particles are suspended – floating around in the water but not dissolving. The water appears cloudy (turbid) as a result. While the wild children down the street have never yet been suspended from school, the gelatin treats their mother gave them are a more durable suspension of gelatin in water (with flavoring and coloring mixed in as well) known as a colloid.
Homogeneous Mixtures
Uniform mixtures can be misleading – it isn’t always apparent that they aren’t a pure substance. Alloys, for instance, seem to be made of a single metal. In fact, they’re composed of two or more metals, mixed so evenly that their atoms can form regular structures with one another. The brass candlesticks (copper and zinc), the bronze (copper and tin) on the baby shoes, and the steel fencing (iron alloyed with any of a number of elements can be called steel; carbon, nickel, cobalt, etc.) are all alloys.
Air also tends to be a reasonably homogeneous mixture. Because gas is mostly open space, any new components (exhaled carbon dioxide, evaporated water, car emissions, etc.) distribute themselves fairly rapidly through a given space. The atmosphere itself is never entirely uniform, but take a sample of air in a container and the gases will be perfectly mixed in an instant.
Liquid Solutions
While still a homogeneous mixture, solutions in a liquid solvent deserve their own category simply because so much chemistry is performed in solution. Refreshing drink mixes, like Kool-Aid brand drinks, are solutions of sweetener, flavor and coloring in water. Not all beverages are solutions. If the beverage settles and has to be shaken, it’s only a suspension. (Orange juice and milk, for example, though homogenized milk has been mixed so thoroughly that it forms a semi-permanent mixture called an emulsion.) The 50% isopropanol in the medicine cabinet is a solution of isopropanol in water. Similarly, the hydrogen peroxide solution is 0.5% hydrogen peroxide dissolved in water. Under the sink there are cleaners – bleach (sodium hypochlorite dissolved in water) and ammonia glass cleaner (ammonia gas dissolved in water). It’s bad that they have been stored together, since they can react to make toxic hydrochloric gas. Fortunately, the gas will eventually disperse into the air, becoming homogeneous again. In the meantime however, were someone to breathe it in, the results could be quite painful or even fatal.
Mixtures are everywhere you look – paints, wood, glass, ice cream, and so forth. Finding examples is never a challenge. Figuring out the type of mixture, and what the components of the mixture are -that’s when the chemistry starts to get interesting.
