Matter consists of pure substances and mixtures. Pure substances include elements and compounds, which are atoms from two or more elements chemically bonded. Mixtures contain two or more substances that are combined but are not chemically bonded. If you dissolve salt in water, for example, you create a mixture: saltwater. The salt and water are still present, and their chemical compositions are the same after you mix them. If you add heat to that mixture, the water changes in state from a liquid to a gas. After letting all the water evaporate, you’re left with the salt. That physical change separates your mixture back into its two parts: water and salt. Neither creating nor separating a mixture results in a chemical change.
In the passage above, what is the purpose of the underlined sentence?
A
to describe how one mixture can be separated
B
to show how seawater can be useful
C
to explain how to make your own salt
D
to illustrate an effect of evaporation
A
to describe how one mixture can be separated