There are different kinds of matter. Pure substances and mixtures are two categories of matter. Pure substances consist of one type of particle. For example, atoms, elements, compounds, or molecules are all types of pure substances. Their proportions never change. For example, carbon will always have six protons. Likewise, water will always be made of two hydrogens and one oxygen.
On the other hand, mixtures are made of two or more pure substances. Examples of mixtures are salt water, trail mix, salads, or sand. The composition of mixtures is not definitive. For example, every handful of trail mix that I grade is likely to have a different number of almonds, peanuts, chocolate morsels, etc.
Mixtures can be categorized by being either homogeneous or heterogeneous. Homogeneous mixtures are uniform in composition throughout. All solutions are homogeneous mixtures (homo = same). Heterogeneous mixtures are not uniform throughout (hetero = different). Each section of the mixture will have a different ratio of ingredients.
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