Separations of mixtures are considered physical changes. This is because the process of separating mixtures does not alter the chemical composition of the substances involved. Instead, it relies on physical properties such as size, density, solubility, or boiling point to separate the components.
For example, when you filter a mixture of sand and water, the sand is separated from the water based on the size of the particles. The sand and water remain chemically the same; no new substances are formed. Similarly, distillation separates liquids based on their boiling points, but the chemical identity of each liquid remains unchanged.
In contrast, a chemical change involves a chemical reaction where the substances are transformed into new substances with different chemical properties. Since the separation of mixtures does not involve any chemical reactions, it is classified as a physical change.