3 (a) Separating Salt from Water
Like all matter, water is made up of atoms. Just as the 26 letters of the alphabet combine in different ways to form all the words in the English language, about 100 types of atoms combine in different ways to form all types of matter.
Atoms attach together, or bond, to form molecules. Two hydrogen atoms bonded to an oxygen atom form a water molecule. A short way of writing this is to use the chemical formula for water, H2O.
Atoms attach together, or bond, to form molecules. Two hydrogen atoms bonded to an oxygen atom form a water molecule. A short way of writing this is to use the chemical formula for water, H2O.
Suppose you leave a small puddle of liquid water on the kitchen counter. When you come back two hours later, the puddle is gone. Has the liquid water disappeared? No, a physical change happened. The liquid water changed into water vapor (a gas) and mixed with the air. A change in state, such as from a solid to a liquid or from a liquid to a gas, is an example of a physical change. Other examples of physical changes are bending, crushing, breaking, chopping, and anything else that changes only the shape or form of matter.
Elements and compounds are pure substances, but most of the materials you see every day are not. Instead, they are mixtures. A mixture
is made of two or more substances—elements, compounds, or both—that are
together in the same place but are not chemically combined. Mixtures
differ from compounds in two ways. Each substance in a mixture keeps its individual properties. Also, the parts of a mixture are not combined in a set ratio. Compounds and mixtures differ in yet another way. A compound can be difficult to separate into its elements. But, a mixture is usually easy to separate into its components because each component keeps its own properties.
In distillation, a liquid solution is boiled. Components of the mixture that have different boiling points will boil away at different temperatures. As most of the water boils in Figure 10, it is cooled and then collected in a flask. Once the remaining salt water is allowed to dry, or evaporate, only the salt is left.
In distillation, a liquid solution is boiled. Components of the mixture that have different boiling points will boil away at different temperatures. As most of the water boils in Figure 10, it is cooled and then collected in a flask. Once the remaining salt water is allowed to dry, or evaporate, only the salt is left.