When two or more kinds of atoms, molecules, or ions mix and form a homogeneous blend— a mixture that is the same throughout—a solution has been created, whether the blend is a liquid, a solid, or a gas. The air people breathe is a solution of gases—in any given cubic foot or meter of air, the ratio of nitrogen to oxygen, the two main constituents, is the same— roughly 4:1. There are also solid solutions, one example of which is the alloy bronze—a solution of one metal in another. In nature, many varieties of minerals are solid solutions, including a series of common rock-forming minerals called the plagioclase feldspars.
From a chemist’s point of view, however, liquid solutions can be more interesting and versatile than solid or even gaseous solutions. For one thing, liquid solutions are easy to study in the laboratory; for another, many are based on water, which is an excellent solvent-inexpensive and plentiful.
Water forms three different kinds of solutions, depending on the state of the solute (substance) being dissolved, whether it is solid, liquid, or gas. Beer, an aqueous (water-based) solution, demonstrates all three because it contains a liquid solute—alcohol; a gaseous solute—C02; and a solid solute-sugar.
The properties of a solution reflect the homogeneity that is the essence of its definition:
■ The solute remains in solution unless something is added, such as energy or certain other substances, to cause it to precipitate, or separate out.
■ A solution cannot be separated by filtering it, no matter how fine the filter.
■ Solutes are evenly distributed in a solution-gravity has no effect on them, so there is as much solute near the top of the solution as there is near the bottom.
Another property of solutions with many useful applications is the way different solutes affect the freezing or boiling point of the solvent. For instance, salt (NaCI) is often scattered over a frozen sidewalk to lower the melting point of ice and trigger melting. Interestingly, solutes also raise the boiling point of solutions. Salty water has a higher boiling point than pure water.
Read More Solutions, acids, and bases
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