The key differences between a pure substance and a mixture are:
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Definition: A pure substance consists of a single type of particle and has uniform properties throughout. Examples include elements (like gold or oxygen) and compounds (like water or sodium chloride). In contrast, a mixture contains two or more different substances that are not chemically combined and can have variable composition.
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Separation: Pure substances cannot be separated into their components by physical means. Mixtures, however, can be separated by physical methods such as filtration, distillation, or centrifugation because they consist of multiple substances that retain their individual properties.
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Homogeneity: Pure substances are homogeneous, meaning they have a consistent composition and appearance throughout. Mixtures can be heterogeneous (with visibly different components) or homogeneous (solutions) but still contain multiple substances.
Given this, the correct responses highlighting the differences would be:
- A pure substance cannot be separated by physical means.
- Mixtures can be separated by physical means.
The other responses contain inaccuracies. For example, a pure substance is not heterogeneous; it is homogeneous. Similarly, mixtures are made up of two or more substances, not just one.