Malaquita

The Preparation and Verification of Malachite
Original source: Joseph S. Schmuckler and Cheryl J. Snyder, Temple University, Philadelphia, PA 19122, Chemistry, Vol. 48, No. 11, 19-20, December 1975 With modifications by David A. Katz, Pima Community College, Tucson, AZ 85709

Malachite, a mineral of copper, is one of the most beautiful minerals known. In the natural state, this relatively softmineral usually shows various tints of green, varying from a dark, rich green to bright Kelly green. Since earliest civilizations, it has been carved into art forms or semiprecious jewelry, or ground into a fine powder for use as an artist's pigment (1). Today, tourists to Elat, a city on the Gulf of Akaba, can purchase "stones of Elat" which are malachite-bearing rocks. King Solomon's mines,mentioned in the Bible, are believed to have been located there. Malachite is found in dry or semiarid regions, usually near the surface, and is a good indicator of deeper copper deposits. Chemically, it is a combination of copper(II) carbonate and copper(II) hydroxide, CuCO3 Cu(OH)2. In the history of chemistry, malachite has been important, too. In the early 1800’s, a controversy existed about thenature of compounds and mixtures. At that time, Claude Louis Berthollet (1748-1822) was publishing his findings about the varied composition of compounds. A book (2) on the history of that period states "Unfortunately Berthollet drew incorrect conclusions from some of his [own] experiments, holding that the composition of certain compounds may vary within small limits." During this same period,another chemist, Louis Joseph Proust (1754-1826) had already completed chemical analysis on samples of malachite obtained from various natural sources. His findings showed without doubt that the composition of malachite was the same (2), regardless of its source: "[Berthollet's incorrect conclusions were] quickly noted by Proust, who, in a series of researches continued until about 1808, establishedthe law of definite proportions ... thus ending the famous controversy between the two men ...." and, also, ending the confusion about what is a mixture and what is a compound. But still, another chemist of the same period, Jeremias Benjamin Richter (1762-1807) was working on the same topics and was much aware of the controversy about mixtures and compounds and its resolution. Impact of theresolution on his own work (2) is reflected in his writing: ". . . the science of measuring the quantitative proportions ... of the masses in which chemical elements stand in regard to each other [in a compound]." Beginning students of chemistry might be interested to know that Richter coined the term, stoichiometry. Malachite and the beautiful blue azurite are two of the most common ores of copper.Today it is indeed sad to note that as we, in this highly industrialized society, use up the Earth's supply of copper, malachite and azurite becomes more and more scarce. If this continues, one day soon samples of malachite and azurite might be found only in museums. By following the experiment described here, you can make malachite by combining the ingredients, as nature did, perhaps millions ofyears ago. But unlike nature, which required

probably millions of years, you can complete the process during a single laboratory period.

Safety Precautions
Goggles must be worn in the laboratory at all times. Copper(II) nitrate solutions can be irritating to the eyes. Ingestion of solutions can cause vomiting and diarrhea with severe abdominal pain. Ammonia, although dilute in theexperiment, has a strong odor and is irritating to the mucus membranes. If the odor of ammonia is irritating to you, work with the ammonia under a hood. Nitric acid, although dilute in this experiment, is corrosive to the skin. In the event of skin contact, wash the affected area with water. Yellow stains on the skin may occur. Hydrochloric acid, although dilute in this experiment, is corrosive to the...