What Is a Mixture?
Before diving into specific types of mixtures, it helps to be clear about what a mixture actually is.
A mixture is a combination of two or more substances that are not chemically bonded together. The substances keep their individual properties and can, in principle, be separated by physical means.
This is different from a compound, where elements are chemically joined and form an entirely new substance. In a mixture, no new substance is created — you simply have two or more things blended together.
Mixtures are everywhere in daily life:
- The air you breathe is a mixture of nitrogen, oxygen, argon, and other gases
- Blood is a complex mixture of cells, proteins, water, and dissolved salts
- Stainless steel (used in cutlery) is a mixture of metals
- Shampoo is a mixture of water, oils, and other ingredients
Chemists classify mixtures based on how well the components are mixed and the size of the particles involved. This gives us three broad categories:
| Category | Particle Size | Example |
|---|---|---|
| Solution | < 1 nm (molecular/ionic) | Salt water |
| Colloid | 1–1000 nm | Milk, hair gel |
| Suspension | > 1000 nm (visible particles) | Muddy water, sand in water |
Within these categories, we find specific types: solutions, emulsions, alloys, and gels — all of which you will explore in this subtopic.
MYP Key Concept — Change: As you study mixtures, think about how combining substances changes their properties. An alloy is stronger than its component metals; an emulsion behaves differently from either oil or water alone. The concept of change runs through all of materials science.
Global Context — Scientific and Technical Innovation: The development of new mixtures — from ancient bronze alloys to modern hydrogel contact lenses — has driven technological progress throughout human history. As you study each mixture type, consider: what problem was this mixture designed to solve?
Solutions — The Most Familiar Mixture
A solution is probably the type of mixture you encounter most often.
A solution is a homogeneous mixture in which one substance (the solute) is completely dissolved in another (the solvent), producing a mixture with a uniform composition throughout.
The substance that dissolves in a solution. It is usually present in the smaller amount.
The substance that does the dissolving. It is usually present in the larger amount. Water is the most common solvent in everyday life.
Key characteristics of solutions:
- They are transparent (you can see through them, though they may be coloured)
- The particles are incredibly small — at the atomic or molecular level (less than 1 nm)
- The solute particles do not settle out over time
- They cannot be separated by filtration
Salt water is a classic solution. When you stir salt (sodium chloride, NaCl) into water:
- Salt = solute
- Water = solvent
- Salt water = solution
The salt dissolves completely — you cannot see any salt particles, the mixture looks uniform, and if you leave it, the salt does not sink to the bottom.
Water is often called the "universal solvent" in everyday language, but this is actually an oversimplification! Water is excellent at dissolving ionic compounds and polar molecules, but it cannot dissolve oils, many plastics, or most organic compounds. A more accurate statement is that water is a very versatile solvent. Ethanol dissolves many substances that water cannot. Nail polish remover (acetone) and petrol are also solvents used in everyday products.
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