CONCEPT Formed from hydrocarbons, hydrocarbon derivatives, or sometimes from silicon, polymers are the basis not only for numerous natural materials, but also for most of the synthetic plastics that one encounters every day. Polymers consist of extremely large, chain-like molecules that are, in turn, made up of numerous smaller, repeating units called monomers. Chains of […]


CONCEPT There was once a time when chemists thought “organic” referred only to things that were living, and that life was the result of a spiritual “life force.” While there is nothing wrong with viewing life as having a spiritual component, spiritual matters are simply outside the realm of science, and to mix up the […]

Distillation and Filtration

CONCEPT When most people think of chemistry, they think about joining substances together. Certainly, the bonding of elements to form compounds through chemical reactions is an integral component of the chemist’s study; but chemists are also concerned with the separation of substances. Some forms of separation, in which compounds are returned to their elemental form, […]


CONCEPT The term osmosis describes the movement of a solvent through a semipermeable membrane from a less concentrated solution to a more concentrated one. Water is sometimes called “the perfect solvent,” and living tissue (for example, a human being’s cell walls) is the best example of a semipermeable membrane. Osmosis has a number of life-preserving […]


CONCEPT We are most accustomed to thinking of solutions as mixtures of a substance dissolved in water, but in fact the meaning of the term is broader than that. Certainly there is a special place in chemistry for solutions in which water—”the universal solvent”—provides the solvent medium. This is also true in daily life. Coffee, […]


CONCEPT Elements and compounds are pure substances, but much of the material around us—including air, wood, soil, and even (in most cases) water— appears in the form of a mixture. Unlike a pure substance, a mixture has variable composition: in other words, it cannot be reduced to a single type of atom or molecule. Mixtures […]


Acid-base reactions

CONCEPT To an extent, acids and bases can be defined in terms of factors that are apparent to the senses: edible acids taste sour, for instance, while bases are bitter-tasting and slippery to the touch. The best way to understand these two types of substances, however, is in terms of their behavior in chemical reactions. […]

Acids and Bases

CONCEPT The name “acid” calls to mind vivid sensory images—of tartness, for instance, if the acid in question is meant for human consumption, as with the citric acid in lemons. On the other hand, the thought of laboratory- and industrial-strength substances with scary-sounding names, such as sulfuric acid or hydrofluoric acid, carries with it other […]