Alloys, solutions, and mixtures


 When two substances are mixed together, they may react to form a chemical compound, if they do not react, they form a mixture. The constituents of a chemical compound cannot be separated by physical or mechanical methods. The constituents of a mixture, on the other hand, can be separated. For example, a mixture of salt and sand can be separated by dissolving the salt in water. And a solution of salt in water can be separated by evaporating or distilling off the water.

Alloys are made by melting together a metal and one or more other substances (usually also metals) to produce a new material with different physical properties. Alloying aluminum with copper, for example, produces an alloy with a greater hardness, although with less than 60 per cent copper the melting point is lowered. All alloys of zinc and copper, on the other hand, have melting points higher than that of pure zinc.

Alloys

An alloy consists of a metallic element and one or more other, usually metallic, elements. For example, most gold used in jewelry consists of an alloy of gold and smaller amounts of copper or nickel. Most alloys are solidified solutions, but in some alloys chemical bonds form between the constituents.

Solutions

When one substance dissolves in another, the two substances are known respectively as the solute and the solvent. The solute dissolves because the attractive forces between its molecules and the solvent molecules are greater than those that hold its own molecules together. When a substance such as sugar is added to water, molecules of sugar begin to leave the crystals and mix with the water molecules. Ionic substances such as salts break up into positive and negative ions; common salt, for example, breaks up into sodium (Na+) and chloride (Cl-) ions.

Properties of solutions

Dissolving a substance in a liquid raises the boiling point and lowers the freezing point of the liquid. This is why antifreeze is added to the water in a car radiator. And, following the same principle, salt is sometimes used to melt ice on roads.

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