CHEMISTRY GLOSSARY

water jet vacuum pump    →   vodena sisaljka

The water jet vacuum pump or vacuum aspirator is one of the most popular devices that produces vacuum in laboratories. The rapid flow of water through the device creates a vacuum in a side-arm that is connected to a vacuum application such a Buchner flask. The water jet vacuum pump creates a vacuum by means of Venturi effect named after the Italian physicist Giovanni Battista Venturi (1746–1822). The Venturi effect is the reduction in fluid pressure that results when a fluid flows through a constricted section of pipe. Water jet pumps are manufactured of glass, plastic or metal, depending on the conditions in which they are used.

aqueous solution    →   vodena otopina

Aqueous solutions are those solutions where water is the solvent. An aqueous solution found in an equation describing a chemical reaction is denoted by the state symbol, (aq).

water gas    →   vodeni plin

Water gas (blue gas, synthesis gas) is a fuel gas used in industrial synthesis of organic chemicals, and in welding, glassmaking, and other high-temperature industrial applications. Water gas is made by passing steam over a bed of hot coal or coke. It mainly consists of carbon monoxide (CO) and hydrogen (H₂), contaminated with small amounts of CO₂, N₂, CH₄, and O₂.

Buchner flask    →   Buchnerova tikvica

Büchner flask (also known as a vacuum flask, filter flask, side-arm flask or Kitasato flask) is a thick-walled Erlenmeyer flask with a side arm to which a vacuum can be applied.

graduated pipette    →   graduirana pipeta

Graduated pipettes (Mohr pipette) have a scale divided into units of one and of 1/10th of a millilitre. Because of their wide necks it is less accurate than the volumetric pipette. They are used when taking volume of solutions in which accuracy does not have to be very high. By sucking in (with mouth, propipette or a water pump) the liquid is pulled in a little bit above the mark and the opening of the pipet is closed with a forefingertip. Outer wall of pipet is wiped and, with a slight forefinger loosening, the liquid is released until it reaches the mark 0. A pipette is emptied out by lifting the forefinger off and letting the liquid flow out of the pipette freely.

pipette    →   pipeta

Pipettes are glass tubes which are tapers towards at both ends into narrow opened tubes. According to their design two types of pipettes can be distinguished:

Volumetric pipettes

Volumetric pipettes (transfer or belly pipette) are used in volumetric analysis, when there is a need for taking exact smaller volume of a sample solution or reagent. The upper tube of volumetric pipette has a ringlike marking (mark) which marks its calibrated volume. Pipettes calibrated to deliver (TD or Ex) the indicated volume. By sucking in (with mouth, propipette or a water pump) the liquid is pulled in a little bit above the mark and the opening of the pipet is closed with a forefingertip. Outer wall of pipet is wiped and, with a slight forefinger loosening, the liquid is released until it reaches the mark. Mark must figure as a tangent on a lower edge of the liquid meniscus. A pipette is emptied out by lifting the forefinger off and letting the liquid flow out of the pipette freely. After another 15 s and the tip of the pipette is pulled onto the inner wall of the vessel. It is absolutely forbidden to blow out the contents of the pipette

Graduated pipettes

Graduated pipettes (Mohr pipette) have a scale divided into units of one and of 1/10th of a millilitre. Because of their wide necks it is less accurate than the volumetric pipette. They are used when taking volume of solutions in which accuracy does not have to be very high. They are filled in the same way as volumetric ones and liquid can be gradually released.

volumetric pipette    →   prijenosna pipeta

Volumetric pipettes (transfer or belly pipette) are used in volumetric analysis, when there is a need for taking exact smaller volume of a sample solution or reagent. The upper tube of volumetric pipette has a ringlike marking (mark) which marks its calibrated volume. Pipettes calibrated to deliver (TD or Ex) the indicated volume. By sucking in (with mouth, propipette or a water pump) the liquid is pulled in a little bit above the mark and the opening of the pipet is closed with a forefingertip. Outer wall of pipet is wiped and, with a slight forefinger loosening, the liquid is released until it reaches the mark. Mark must figure as a tangent on a lower edge of the liquid meniscus. A pipette is emptied out by lifting the forefinger off and letting the liquid flow out of the pipette freely. After another 15 s and the tip of the pipette is pulled onto the inner wall of the vessel. It is absolutely forbidden to blow out the contents of the pipette.

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.

acid    →   kiselina

Acid is a type of compound that contains hydrogen and dissociates in water to produce positive hydrogen ions. The reaction for an acid HA is commonly written:

In fact, the hydrogen ion (the proton) is solvated, and the complete reaction is:

This definition of acids comes from the Arrhenius theory. Such acids tend to be corrosive substances with a sharp taste, which turn litmus red and produce colour changes with other indicators. They are referred to as protonic acids and are classified into strong acids, which are almost completely dissociated in water, (e.g. sulphuric acid and hydrochloric acid), and weak acids, which are only partially dissociated (e.g. acetic acid and hydrogen sulphide). The strength of an acid depends on the extent to which it dissociates, and is measured by its dissociation constant.

In the Lowry-Brønsted theory of acids and bases (1923), the definition was extended to one in which an acid is a proton donor (a Brønsted acid), and a base is a proton acceptor (a Brønsted base). An important feature of the Lowry-Brønsted concept is that when an acid gives up a proton, a conjugate base is formed that is capable of accepting a proton.

Similarly, every base produces its conjugate acid as a result of accepting a proton.

For example, acetate ion is the conjugate base of acetic acid, and ammonium ion is the conjugate acid of ammonia.

As the acid of a conjugate acid/base pair becomes weaker, its conjugate base becomes stronger and vice versa.

A further extension of the idea of acids and bases was made in the Lewis theory. In this, a G. N. Lewis acid is a compound or atom that can accept a pair of electrons and a Lewis base is one that can donate an electron pair. This definition encompasses "traditional" acid-base reactions, but it also includes reactions that do not involve ions, e.g.

in which NH₃ is the base (donor) and BCl₃ the acid (acceptor).

americium    →   americij

Americium was discovered by Glenn T. Seaborg, Ralph A. James, Stanley G. Thompson and Albert Ghiorso (USA) in 1944. Named for the American continent. It is silvery-white, artificially produced radioactive metal. Americium was produced by bombarding plutonium with neutrons. Americium-241 is currently used in smoke detectors.