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The United Nations has proclaimed 2019 the International Year of the Periodic Table of Chemical Elements (IYPT2019). The same year also marks the 150th anniversary of the publication of Russian chemist Dmitri Mendeleev’s periodic table, containing…

A powdered, granular, or pelleted form of amorphous carbon characterized by very large surface area per unit volume because of an enormous number of fine pores. Activated carbon is capable of collecting gases, liquids, or dissolved substances on the…

The application of chemistry to the technical examination, authentication, and preservation of cultural property. Chemists working in museums engage in a broad range of investigations, most frequently studying the chemical composition and structure…

An instrument for weighing. The word “balance,” derived from the Latin bilanx (“having two pans”), is often used interchangeably with “scale” or “scales” (Old English, meaning dishes or plates). However, balance is the preferred term for an…

A method for quantitatively determining the concentration, biological activity, or potency of a substance by its effect on the growth of a suitable animal, plant, or microorganism under controlled conditions. A bioassay (biological assay) is a…

A biochemical reaction involving the transfer of a negatively charged electron from one organic compound to another organic compound or to oxygen. Biological oxidation is an energy-producing reaction in living cells, and it is coupled with a…

A colorless, odorless gas at atmospheric temperature and pressure, CO2, with a molecular weight of 44.009 g/mol. Under normal conditions, it is stable, inert, and nontoxic (see illustration). Ball-and-stick model of carbon dioxide. Red = oxygen.…

The phenomenon in which a relatively small amount of foreign material, called a catalyst, speeds up the rate of a chemical reaction without itself being consumed. A catalyst is a material, and not light or heat. It increases a reaction rate. For…

A chemical element, Cl, atomic number 17 and atomic weight 35.453. Chlorine exists as a greenish-yellow gas at ordinary temperatures and pressures (see illustration). It is second in reactivity only to fluorine among the halogen elements, and hence…

A hydroxytricarboxylic acid, general formula C6H8O7. Citric acid (see illustration) and its salts are widely used because they are nontoxic, safe to handle, and easily biodegraded. They are universally accepted, without restriction on level, as food…

Volatile, fragrant oils obtained from plants. Essential oils are distinguished from those known as fixed oils, which are mainly triglycerides of fatty acids. Essential oils have been obtained from thousands of plants (Fig. 1) and are designated and…

An active and intentional act or practice of putting to death, in a relatively painless way, of persons suffering severely from medical conditions that are incurable, untreatable, or irreversible. Euthanasia is an act by a person, usually a…

Fentanyl is a synthetic opioid analgesic (pain reliever) that resembles morphine in its action. However, its drug potency is approximately 50 to 100 times more powerful than that of morphine, leading to high rates of both addiction and overdose…