CHEMISTRY GLOSSARY

X-ray diffraction pattern    →   rendgenski difrakcijski uzorci

X-ray diffraction pattern is an interference pattern created by x-rays as they pass through a solid material. Studying X-ray diffraction patterns gives detailed information on the three-dimensional structure of crystals, surfaces, and atoms.

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X-ray crystallography    →   rendgenska kristalografija

X-ray crystallography is a determination of a three dimensional arrangements of atoms in a crystal by analysis of X-ray diffraction patterns.

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X-ray diffraction    →   rendgenska difrakcija

The regular array of atoms in a crystal is a three-dimensional diffraction grating for short-wavelength waves such as X-rays. The atoms are arranged in planes with interplanar spacing d. Diffraction maxima occur in the incident direction of the wave, measured from the surface of a plane of atoms, and the wavelength λ of the radiation satisfy Braggs’s law:

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diffraction grating    →   difrakcijska rešetka

Diffraction grating is a series of slits used to separate an incident wave into its component wavelengths by directionally separating their diffraction maxima.

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X-ray tube    →   rendgenska cijev

X-ray tube is a cathode ray tube that focuses energetic streams of electrons on a metal target, causing the metal to emit X-rays. The basic principle of the X-ray tube has not changed significantly since Roentgen's 1895 discovery. Current applied to a metal cathode (about 50 000 V) produces free electrons. The X-rays are produced when the rapidly moving electrons are suddenly stopped as they strike the metal target of the tube.

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Avogadro constant    →   Avogadrova konstanta

Avogadro constant (N_A or L) is the number of elementary entities in one mole of a substance.

It has the value (6.022 045±0.000 031)×10²³ mol^-1.

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Bragg angle    →   Braggov kut

Bragg angle (Θ) is the angle between an incident X-ray beam and a set of crystal planes for which the secondary radiation displays maximum intensity as a result of constructive interference. British physicist Sir William Henry Bragg and his son Sir William Lawrence Bragg developed a simple relation for scattering angles, now call Bragg’s law.

which relates the angle θ between a crystal plane and the diffracted X-ray beam, the wavelength λ of the x-rays, the crystal plane spacing d, and the diffraction order n (any integer).

The diffraction experiment as presently considered is intended to provide quantitative information on the lattice constant and shape characteristics of the unit cell.

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monochromator    →   monokromator

Monochromator (from the Greek words mono and chroma meaning single and colour) is an optical device based on dispersion of light by one or more prisms or diffraction gratings into its constituent wavelengths, which are utilized in turn.

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X-rays    →   X-zrake

X-rays are electromagnetic radiation of shorter wavelength than ultraviolet radiation (10^-11 m to 10^-9 m or 0.01 nm to 1 nm) produced by bombardment of atoms by high-quantum-energy particles. X-rays can pass through many forms of matter and they are therefore used medically and industrially to examine the internal structure.

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Schrotter apparatus for determination of CO2    →   Schrotterova aparatura za određivanje CO2

Schrötter decomposition apparatus (Schrötter's alkalimeter) is used to determining the carbonate content in samples of limestone, gypsum, dolomite, or baking powder by loss of weight. The apparatus is named after the Austrian chemist Anton Schrötter von Kristelli (1802-1875), who devised it in 1871. The size of the filled apparatus (apparatus is 16 cm high) is such that it weights less than 75 g, and can be placed on the pan of an analytical balance.

Procedure: Weigh about 0.5 g of the powdered carbonate sample and introduce it into the decomposition flask C. Pour into the drying tube A 2-3 mL of concentrated sulphuric acid (H₂SO₄), and to the dropping funnel B add about 10-15 mL of hydrochloric acid (w(HCl) = 15 %). Weigh the whole apparatus. Open the upper taps of both parts and allow the hydrochloric acid from B to run slowly down on to the powdered sample. The evolved CO₂ escapes through the strong sulphuric acid and is thus thoroughly dried. When further addition of acid produces no more evolution of CO₂, warm the apparatus up to 80 °C so as to expel the CO₂ from the solution. Connect the upper tap of the drying tube A to a water pump and draw a slow current of air through the apparatus until completely cool. Open the upper taps for a moment to equalize the internal and external pressure and weight the apparatus again. The weight loss is equal to the weight of carbon dioxide liberated from the carbonates.

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