CHEMISTRY GLOSSARY

helium    →   helij

Helium was discovered by Pierre Jules César Janssen (France) and Sir William Ramsay (Scotland) in 1868. The origin of the name comes from the Greek word helios meaning sun. It is light, odourless, colourless inert gas. Second most abundant element in the universe. Helium is found in natural gas deposits from wells in Texas, Oklahoma and Kansas. Used in balloons, deep sea diving and welding. Also used in very low temperature research.

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Henry’s law    →   Henryjev zakon

Henry’s law was discovered in 1801 by the British chemist William Henry (1775-1836). At a constant temperature the mass of gas dissolved in a liquid at equilibrium is proportional to the partial pressure of the gas. It applies only to gases that do not react with the solvent.

where p_i is the partial pressure of component i above the solution, x_i is its mole fraction in the solution, and K_x is the Henry’s law constant (a characteristic of the given gas and solvent, as well as the temperature).

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ideal gas law    →   jednadžba stanja idealnog plina

The generalized ideal gas law is derived from a combination of the laws of Boyle and Charles. Ideal gas law is the equation of state

which defines an ideal gas, where p is pressure, V molar volume, T temperature, and R the molar gas constant (8.314 JK^-1mol^-1).

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invert sugar    →   invertni šećer

Invert sugar is a mixture of equal parts of glucose and fructose resulting from the hydrolysis of sucrose (saccharose). The name stemming from the fact that it rotates of plane polarized light in the opposite direction of sucrose. Sucrose is dextrorotatory - it rotates polarized light clockwise ([α]_D = +66.5°). Invert sugar rotates the plane of the polarized light counterclockwise ([α]_D = -22°) due to the strongly levorotatory nature of fructose ([α]_D = -92°).

Homemade artificial honey (invert sugar syrup): Dissolve two parts of household sugar (1 kg) with stirring in one part of water (0.5 kg) in a saucepan over low heat. Add 1 g of citric acid or the juice of one lemon to the mixture. Bring the ingredients to a slow boil. It can take anywhere between 15 minutes to 1 hour. The end result is sticky, golden syrup. Let it sit at room temperature until it is cool.

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Joule-Thomson coefficient    →   Joule-Thompsonov koeficijent

Joule-Thomson coefficient (μ) is a parameter which describes the temperature change when a gas expands adiabatically through a nozzle from a high pressure to a low pressure region. It is defined by

where H is enthalpy.

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Joule-Thomson’s effect    →   Joule-Thomsonov efekt

Temperature of ideal gas will not be changed when it is repressed to a lower pressure, but when real gases are repressed to a lower pressure, a lower or higher temperature change appears under high pressures. The temperature change which appears at real gas expansion in a system into which energy is not brought is called Joule-Thomson’s effect. It was determined that when air is repressed by 1 bar, its temperature drops by 0.25 °C. That minute effect is completely irrelevant for most technical processes, but is also used in gas liquefying procedure.

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kelvin    →   kelvin

Kelvin (K) is the SI base unit of thermodynamic temperature.

The kelvin, unit of thermodynamic temperature, is the fraction 1/273.16 of the thermodynamic temperature of the triple point of water. The unit was named after the British scientist Sir. W. Thompson, Lord Kelvin (1824-1907).

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kinetic energy    →   kinetička energija

Kinetic energy (E_k) is associated with the state of motion of a body. It is a scalar property and defined to be

Kinetic energy is most clearly exhibited in gases, in which molecules have much greater freedom of motion than in liquids and solids.

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lime    →   živo vapno

Lime (or quicklime) is the common name for calcium oxide (CaO). It is manufactured from limestone, CaCO₃, by heating it to a high temperature (about 1 000 °C). At this temperature carbon dioxide, CO₂, is released from the limestone creating calcium oxide, CaO.

A further process involves adding water in a process known as hydrating, which produces hydrated, or slaked lime [Ca(OH)₂].

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Knudsen burette    →   Knudsenova bireta

Knudsen's automatic bulb-burette, developed by the Danish physicist Martin Knudsen (1871-1949), is designed in a way that even routine field analysis in a boat laboratory would provide highly accurate measurements. The burette is filled with a mixture of silver nitrate from reservoir R, located above the burette, by opening the A valve. When the solution crosses the three-way C valve the A valve is closed preventing further solution flow in to the burette. Any extra solution is caught in the W bowl. Turn the C valve, which marks the zero on the scale, in order to allow atmospheric air to enter the burette. Since most open-ocean samples lie in a relatively small chlorinity range, the burette is designed so that much of its capacity is in the bulb (B). This allows the titration to be quick (by quickly releasing contents from the B area) and reduces the error that occurs from the slow drainage along the inner wall of the burette.

Each millimeter is divided in to twenty parts (double millimeter division of the Knudsen burette) which allows for highly accurate measurements (the scale is read up to a precision of 0.005 mL). From 0 to 16 the burette isn't divided, that usually starts from 16 and goes until 20.5 or 21.5. A single double millimeter on a Knudsen burette scale corresponds to one permille of chloride in the seawater sample. This burette can be used for titration of water from all of the oceans and seas, with the exemptions being areas with very low salinity (e.g. the Baltic Sea) and river estuaries which require the use of normal burettes.

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