HOMOGENEOUS MIXTURE: CHARACTERISTICS AND EXAMPLES - CHEMISTRY - 2025

A homogeneous mixture is one whose components establish a uniform material phase; that is to say, that seen in the physical scale allowed by our vision, there is no difference in its composition nor in its properties. This means that its components (solutes) cannot be separated by simple mechanical techniques.

In chemistry, homogeneous mixtures are quite common, since they consist of any solution or solution that is prepared in the laboratory and that does not show two phases; one solid and the other liquid, usually when, for example, precipitation occurs.

However, homogeneous mixtures encompass more than solutions (aqueous or organic) with dissolved solutes (gaseous, liquid, or solid). They can also be gaseous or solid, as long as they appear visibly uniform; just like the whipped cream in the picture above.

The homogeneity of a mixture or material depends on the scale with which it is considered, either micro or macroscopically, being therefore sometimes a mere matter of perspective. However, the criteria of composition, distribution, structures and properties are also used to affirm or not if a mixture is homogeneous.

Some examples of homogeneous mixtures are air, salt or sugar water, metal alloy, vodka or vinegar, although we will explain more below.

Characteristics of homogeneous mixtures

A cup with whipped cream: an example of a homogeneous mixture. Source: Wendy Drummer via Pexels.

They are uniform and isotropic

All homogeneous mixtures, regardless of their material phase, have one constant in common: they are uniform in their properties, visible or microscopic, physical or chemical. Of course, these criteria are applied when it is not enough to observe a single phase or if you want to differentiate two mixtures from each other according to their homogeneity.

For example, a glass to which oxides have been added to color it yellow is a homogeneous mixture, since at the first glance it is uniform throughout (regardless of its shape or geometry). Likewise, it is isotropic, since its properties do not vary in the direction of the glass where they are measured.

Thus we now have two characteristics of homogeneous mixtures: they are uniform and isotropic; although isotropy does not always imply homogeneity by itself. Said uniformity also refers to its composition and the distribution of the components or solutes.

For example, in the case of whipped cream, there can be no greasier or sweeter areas than others. No matter where a spoonful of it is taken, as long as it has been made with the same recipe, the cream will be uniform and homogeneous, even if some differences in the tones of its colors can be perceived.

Its components are mechanically inseparable

Heterogeneous mixtures are characterized in that their components can be separated manually or mechanically; while the same does not happen with homogeneous mixtures, requiring other separation techniques. This is due to the fact that the main phase or solvent manages to incorporate and efficiently distribute the solutes.

Returning to the whipped cream, it is not possible to obtain all the ingredients that were used to prepare it directly or mechanically; sugar, fat, and air are scrambled and it takes more than an instrument to separate them. The same goes for gold glass.

The size of its solute particles is very small

Homogeneous mixtures are uniform and inseparable because, in addition to the effective distribution of their components or solutes, their size is very small. In whipped cream, the solvent phase is fat, while the solute is essentially air. Air bubbles are too small to be seen on the surface.

It is now appropriate to refer to aqueous solutions of salts. The salt particles are too small to coalesce and settle at a constant temperature, and without the water evaporating. There is no technique or filters (at least not conventional) that manage to remove salts from the water without the need to distill or evaporate it.

They tend to be microscopically uniform

There are mixtures that appear uniform but when viewed on a reduced scale, they become heterogeneous. Even so, as long as the distribution of these components is uniform, it can be assumed that the mixture continues to be homogeneous; that is, they must be arranged in such a way that there are no “internal phases”.

This is where the homogeneity of our whipped cream is called into question: are the microscopic fat and air particles evenly distributed? Is this distribution constant throughout the cream?

If the answers are yes, then the cream is still homogeneous; otherwise, as would happen if there are parts where there is more fat or air than in others, it is said to be heterogeneous. This happens because the whipped cream is a colloid, which are homogeneous mixtures, but are microscopically heterogeneous.

Examples of homogeneous mixtures

Aqueous solutions

Water is the universal solvent. When one or more highly soluble solutes are dissolved in it, transparent or colored solutions are obtained, which are homogeneous. Salt water (from the seas) or sugar (for juices or drinks) are therefore examples of homogeneous mixtures.

Among these aqueous solutions (and some liquid products) we can also mention: coffee (without cream), vinegar, wines, beers, oil, liquid soaps, soft drinks (without shaking), indicator solutions, glues, sodium hydroxide, hydrochloric acid, syrups, solutions of transition metal salts, etc.

Colloids

Although they may not be microscopically homogeneous, their particle size is still too small to be easily observed or separated.

Among some colloids we have: cigarette smoke, haze, lipstick, mayonnaise, cheese, jellies, milk, whipped cream, ice cream, paints, etc.

Air

Air is a perfect example of a homogeneous gas mixture, since it consists of several gases (nitrogen, oxygen, argon, water vapor, etc.) that cannot be differentiated with the naked eye; however, they can be separated if subjected to liquefaction and then fractional distillation.

Alloys

Alloys are examples of homogeneous solid mixtures, since the metals can no longer be separated and also integrate the same crystal.

That is why steels are homogeneous mixtures, because no matter what forms they take (plates, chains, beams, etc.) the composition and their properties are constant wherever they are determined. The same applies to amalgams, galinstan, bronze, pewter and white gold.

Others

Note that there comes a point where mixtures begin to be considered materials due to their applications. This is how we have, in addition to alloys, glasses and ceramics (of a single color). Likewise, some woods and plastics may be considered homogeneous mixtures, as well as stones or textile fibers.

References

1. Whitten, Davis, Peck & Stanley. (2008). Chemistry (8th ed.). CENGAGE Learning.
2. Helmenstine, Anne Marie, Ph.D. (September 21, 2019). The Difference Between Heterogeneous and Homogeneous Mixtures. Recovered from: thoughtco.com
3. Erin Noxon. (2019). Homogeneous Mixture Definition: Lesson for Kids Video. Study. Recovered from: study.com
4. CK-12 Foundation. (October 16, 2019). Homogeneous Mixture. Chemistry LibreTexts. Recovered from: chem.libretexts.org
5. Chemicool Dictionary. (2017). Definition of Homogeneous. Recovered from: chemicool.com
6. Wikipedia. (2019). Homogeneous and heterogeneous mixtures. Recovered from: en.wikipedia.org