Classify the following as solutions or heterogeneous mixtures: (a) 14 karat gold (prepared by mixing 10 parts molten copper with 14 parts molten gold and then allowing the substance to cool until it solidifies) (b) Filtered ocean water (c) A piece of wood (d) Your exhaled breath (e) A bottle of salad oil and vinegar shaken extremely well

In the world of chemistry, a solution is a special type of mixture where two or more substances are so intimately mixed that they behave as a single phase. This often means that one substance, known as the solute, is dissolved in another, called the solvent. An everyday example can be seen when table salt (solute) dissolves in water (solvent) to form a saline solution.

When discussing solution chemistry, the property of uniform distribution is key. That is, the particles of the solute are dispersed at a molecular or ionic level and are evenly distributed throughout the solvent. Solutions do not allow light to scatter when it passes through them, a phenomenon known as the Tyndall effect. This is why solutions like filtered ocean water or the air we exhale are clear and transparent.

Mixtures are composed of two or more substances that retain their individual properties and can be separated by physical means. The physical properties of a mixture, such as boiling point, melting point, and density, are determined by its components.

For example, a piece of wood maintains the properties of the cellulose, lignin, and other compounds it's composed of. These substances are not uniformly distributed, hence the physical properties of wood can vary depending on the specific composition and structure. Another key property of mixtures is the way they interact with light. Heterogeneous mixtures, in particular, often scatter light, a feature that can be used to distinguish them from solutions.

The difference between homogeneous and heterogeneous mixtures lies in how evenly the component substances are mixed.

A homogeneous mixture, also known as a solution, has the same composition throughout. If you take any sample of a homogeneous mixture, like exhaled breath or a 14 karat gold alloy, its composition will be consistent. On the other hand, heterogeneous mixtures have an inconsistent composition. Wood and oil-and-vinegar salad dressing are classic examples of heterogeneous mixtures. No matter how well you shake the salad dressing, oil and vinegar will eventually separate due to their differences in density and polarity. Similarly, wood has varying compositions throughout its structure, which can include air pockets and different types of cells, making its composition vary from one section to another.