A mixture results when two substances are physically combined but don’t chemically react. The two types of mixtures are homogeneous mixtures and heterogeneous mixtures. Here are 10 examples of mixtures and a look at whether they are homogeneous or heterogeneous.
Homogeneous Mixtures
A homogeneous mixture is one which appears to have uniform composition. Samples taken from different parts of a homogeneous mixture have the same chemical composition. A homogeneous mixture consists of a single phase (e.g., solid, liquid, gas).
Heterogeneous Mixtures
A heterogeneous mixture lacks a uniform composition. Samples taken from different parts of the mixture don’t have the same composition. Usually, you can mechanically separate the components of a heterogeneous mixture (e.g., removing rocks from a mixture of rocks and sand). The constituents of a heterogeneous mixture may be the same phase (e.g., oil and water, which are both liquids) or different phases (olives in oil, which are a solid and a liquid).
Examples of Mixtures
- Air is a homogeneous mixture of gases. However, the Earth’s atmosphere is a heterogeneous mixture because it contains clouds.
- Alloys are usually homogeneous mixtures of metals. Examples of homogeneous alloys include bronze, brass, 14K gold, steel, amalgam, and sterling silver. However, some alloys contain multiple phases and are heterogeneous mixtures.
- Unless solids are melted together, they are usually heterogeneous mixtures. Examples include a mixture of colored candies, a box of toys, salt and sugar, salt and sand, a basket of vegetables, and a box of toys.
- Mixtures with two phases are always heterogeneous mixtures. Examples include ice in water, salt and oil, noodles in broth, and sand and water.
- Many common liquids are homogeneous mixtures. Examples include dishwashing liquid, shampoo, vinegar, wine, and vodka.
- Similarly, many common liquids are heterogeneous mixtures. Examples include orange juice with pulp and salad dressing.
- Immiscible liquids form heterogeneous mixtures. Examples include oil and water, molten silver and lead, and pentane and acetic acid.
- Chemical solutions are homogeneous mixtures that have the same phase as their solvent.
- Some homogeneous mixtures are components of heterogeneous mixtures. For example, bitumen is a homogeneous mixture that is a component of asphalt (a heterogeneous mixture).
- Some mixtures appear homogeneous from a distance, but are heterogeneous upon closer inspection. Examples include soil, blood, and sand.
When Identifying Homogeneous and Heterogeneous Gets Tricky
Some mixtures appear homogeneous to the naked eye, but are heterogeneous upon magnification. Blood is a good example. The liquid and different cells aren’t visible except under a microscope.
Sometimes a mixture can switch between homogeneous and heterogeneous, depending on conditions. For example, an unopened bottle of soda is a homogeneous mixture. When the bottle is opened and pressure drops, carbon dioxide bubbles form. The bubbles in the liquid make it a heterogeneous mixture.
Examples That Are Not Mixtures
Technically, whenever you combine two or more substances and a chemical reaction occurs, the result isn’t a mixture (at least until it’s finished reacting).
- Combining ingredients to bake cookies or a cake forms what is called a “mixture” in cooking. But, a chemical reaction occurs between the ingredients. The final result (cookies or a cake) is a heterogeneous mixture.
- Combining baking soda and vinegar causes a chemical reaction. The end result could be a solution of sodium acetate in water or a mixture containing water, sodium acetate, and either excess vinegar or undissolved baking soda.
References
- IUPAC (1997). “Mixture.” Compendium of Chemical Terminology (2nd ed.). (the “Gold Book”). Oxford: Blackwell Scientific Publications. ISBN:0-9678550-9-8. doi:10.1351/goldbook
- Weast R. C., Ed. (1990). CRC Handbook of Chemistry and Physics. Boca Raton: Chemical Rubber Publishing Company. ISBN 978-0-8493-0470-5.
- Whitten, K.W.; Gailey, K. D.; Davis, R. E. (1992). General Chemistry (4th ed.) Philadelphia: Saunders College Publishing. ISBN 978-0-03-072373-5.