A mixture cannot have a unique chemical formula because it is not a pure substance. A mixture is a combination of two or more substances that are not chemically combined. The composition of a mixture can vary, and the substances in a mixture can be separated by physical means, such as filtration or distillation.

A chemical formula represents the composition of a pure substance. It indicates the number and type of atoms that are present in a molecule of the substance. A chemical formula can be used to calculate the molecular weight of a substance and to determine its chemical properties.

Because a mixture is not a pure substance, it does not have a unique chemical formula. The composition of a mixture can vary, and the substances in a mixture can be separated by physical means. Therefore, a mixture cannot be represented by a single chemical formula.