CHEMISTRY GLOSSARY

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).

ideal solution    →   idealna otopina

Ideal solution is a solution in which solvent-solvent and solvent-solute interactions are identical, so that properties such as volume and enthalpy are exactly additive. Ideal solutions follow Raoult’s law, which states that the vapour pressure p_i of component i is p_i = x_i p_i^*, where x_i is the mole fraction of component i and p_i^* the vapour pressure of the pure substance i.

Kjeldahl’s method    →   Kjeldahlov postupak

Kjeldahl’s method is an analytical method for determination of nitrogen in certain organic compounds. The method was developed by the Danish chemist Johan Kjeldahl (1849-1900).

It involves addition of a small amount of anhydrous potassium sulphate to the test compound, followed by heating the mixture with concentrated sulphuric acid, often with a catalyst such as copper sulphate. As a result ammonia is formed. After alkalyzing the mixture with sodium hydroxyde, the ammonia is separated by distillation, collected in standard acid, and the nitrogen determined by back-titration.

1. Kjeldahl flask for decomposition (500 ml – macro or 100 ml - micro)
2. funnel for alkaline solution
3. Wagner tube (drop catcher)
4. condenser
5. absorption flask with known volume of standard acid

Knudsen’s pipette    →   Knudsenova pipeta

Kudsen's automatic pipette, developed by the Danish physicist Martin Knudsen (1871-1949), allows quick and accurate transfer of a constant volume of liquid (sea water), usually around 15 mL. On the top of pipette is a double sided C vent that can establish flow between the body of the pipette and one of the branches (A or B), or isolate the body of the pipette from both of the branches. Sucking through the B branch the pipette is filled with liquid, it is closed with a twist of the C valve and the liquid is released by rotating the valve towards the A branch (so atmospheric air can enter the pipette). Emptying the pipette takes around 30 seconds. Before it's first use, the pipette must be calibrated with distilled water.

liquid aggregate state    →   tekuće agregatno stanje

Liquids have a constant volume, but they do not have a constant shape. They assume the shape of a vessel they are in at the moment. It happens because molecules of liquids are still close enough to each other, the attracting forces still being very strong.

mass concentration    →   masena koncentracija

Mass concentration (γ) is equal to mass (m_A) of soluted substance and volume (V) of the solution proportion. SI unit for mass concentration is kg m^-3, but in laboratory practice g dm^-3, which has the same number value, is often used.

measuring cylinder    →   menzura

Measuring cylinders (graduated cylinders) are graduated glass cylinders with a capacity from 2 mL to 2 L. They are used when reagent solutions for volume measuring are prepared when accuracy is not of great relevance. The larger the measuring cylinder, the bigger the measuring error.

meniscus    →   meniskus

Meniscus is the concave curve of a liquid surface in a graduate or narrow tube. Caused by surface tension. Position of eye at all volumetric vessels must be at the same level as the meniscus to avoid a parallax error.

mustard agent    →   plikavac

Mustard agents are usually classified as blistering agents owing to the similarity of the wounds caused by these substances resembling burns and blisters. However, since mustard agents also cause severe damage to the eyes, respiratory system and internal organs, they should preferably be described as blistering and tissue-injuring agents. Normal mustard agent (yperite), 1,1-thio-bis-[2-chloroethane], reacts with a large number of biological molecules. The effect of mustard agent is delayed and the first symptoms do not occur between 2-24 hours after exposure. At room temperature, mustard agent is a liquid with low volatility and is very stable during storage.

naphtha    →   benzin

Naphtha is any of various volatile, highly flammable liquid hydrocarbon mixtures (petroleum ether, ligroin, benzine) used chiefly as solvents and diluents. In petroleum engineering, naphtha is defined as the fraction of hydrocarbons in petroleum boiling between 30 °C and 200 °C.