Examples of homogeneous and heterogeneous mixtures
A homogeneous mixture has the same composition all the way through, so you cannot see its separate parts; it is also called a solution. A heterogeneous mixture is uneven, with parts you can see or that settle out over time. A quick test: if samples taken from different spots could look or behave differently, the mixture is heterogeneous.
Homogeneous mixtures
- Air — nitrogen, oxygen, argon and other gases evenly mixed.
- Salt water — salt dissolved so evenly that you cannot see it.
- Sugar water — sugar molecules spread evenly through the water.
- Vinegar — acetic acid dissolved in water.
- Rubbing alcohol — isopropyl alcohol mixed with water.
- Gasoline — many different hydrocarbons blended into one clear liquid.
- Natural gas — mostly methane, with smaller amounts of ethane, propane and other gases.
- Brass — copper and zinc mixed evenly in a solid alloy.
- Antifreeze coolant — ethylene glycol mixed with water.
- Carbonated water in a sealed bottle — carbon dioxide dissolved in water (once bubbles form, it becomes heterogeneous).
Heterogeneous mixtures
- Sand and water — the sand sinks to the bottom.
- Oil and water — they form two separate layers.
- Salad — each ingredient stays separate and visible.
- Trail mix — nuts, raisins and chocolate you can sort by hand.
- Granite — visible grains of different minerals.
- Soil — particles of different sizes mixed with bits of plant matter.
- Chocolate chip cookie — the chips are clearly separate from the dough.
- Cereal in milk — solid pieces floating in a liquid.
- Orange juice with pulp — the pulp floats in the juice and can be strained out.
- Concrete — pieces of gravel and sand held in cement.
How to tell them apart
Look closely or let the mixture stand. If you can see separate pieces, layers or particles, or if something settles to the bottom, it is heterogeneous. A homogeneous mixture stays uniform and never settles, even after days. The state does not matter: homogeneous mixtures can be gases (air), liquids (vinegar) or solids (brass).
What about milk and fog?
Colloids such as milk, fog and mayonnaise look uniform, but they contain particles large enough to scatter a beam of light, an effect called the Tyndall effect. Because of this, most chemistry courses classify colloids as heterogeneous mixtures.