ConcentrationIn chemistry, concentration is the abundance of a constituent divided by the total volume of a mixture. Several types of mathematical description can be distinguished: mass concentration, molar concentration, number concentration, and volume concentration. The concentration can refer to any kind of chemical mixture, but most frequently refers to solutes and solvents in solutions. The molar (amount) concentration has variants, such as normal concentration and osmotic concentration. Dilution is reduction of concentration, e.
Scanning electron microscopeA scanning electron microscope (SEM) is a type of electron microscope that produces images of a sample by scanning the surface with a focused beam of electrons. The electrons interact with atoms in the sample, producing various signals that contain information about the surface topography and composition of the sample. The electron beam is scanned in a raster scan pattern, and the position of the beam is combined with the intensity of the detected signal to produce an image.
Silver standardThe silver standard is a monetary system in which the standard economic unit of account is a fixed weight of silver. Silver was far more widespread than gold as the monetary standard worldwide, from the Sumerians 3000 BC until 1873. Following the discovery in the 16th century of large deposits of silver at the Cerro Rico in Potosí, Bolivia, an international silver standard came into existence in conjunction with the Spanish pieces of eight. These silver dollar coins played the role of an international trading currency for nearly four hundred years.
Hunsdiecker reactionThe Hunsdiecker reaction (also called the Borodin reaction or the Hunsdiecker–Borodin reaction) is a name reaction in organic chemistry whereby silver salts of carboxylic acids react with a halogen to produce an organic halide. It is an example of both a decarboxylation and a halogenation reaction as the product has one fewer carbon atoms than the starting material (lost as carbon dioxide) and a halogen atom is introduced its place. A catalytic approach has been developed.
PerchlorateA perchlorate is a chemical compound containing the perchlorate ion, ClO4-, the conjugate base of perchloric acid (ionic perchlorate). As counterions, there can be metal cations, quaternary ammonium cations or other ions, for example, nitronium cation (NO2+). The term perchlorate can also describe perchlorate esters or covalent perchlorates. These are organic compounds that are alkyl or aryl esters of perchloric acid. They are characterized by a covalent bond between an oxygen atom of the ClO4 moiety and an organyl group.
Silver as an investmentSilver may be used as an investment like other precious metals. It has been regarded as a form of money and store of value for more than 4,000 years, although it lost its role as legal tender in developed countries when the use of the silver standard came to an end in 1935. Some countries mint bullion and collector coins, however, such as the American Silver Eagle with nominal face values. In 2009, the main demand for silver was for industrial applications (40%), jewellery, bullion coins, and exchange-traded products.
ChloromethaneChloromethane, also called methyl chloride, Refrigerant-40, R-40 or HCC 40, is an organic compound with the chemical formula . One of the haloalkanes, it is a colorless, sweet-smelling, flammable gas. Methyl chloride is a crucial reagent in industrial chemistry, although it is rarely present in consumer products, and was formerly utilized as a refrigerant. Chloromethane is an abundant organohalogen, anthropogenic or natural, in the atmosphere. Laboratory cultures of marine phytoplankton (Phaeodactylum tricornutum, Phaeocystis sp.
AmperometryAmperometry in chemistry is detection of ions in a solution based on electric current or changes in electric current. Amperometry is used in electrophysiology to study vesicle release events using a carbon fiber electrode. Unlike patch clamp techniques, the electrode used for amperometry is not inserted into or attached to the cell, but brought in close proximity of the cell. The measurements from the electrode originate from an oxidizing reaction of a vesicle cargo released into the medium.
