CHEMISTRY GLOSSARY

zwitterion    →   dipolarni ion

Zwitterion, also known as inner salt or dipolar ion, is an ion with a positive and a negative electrical charge at different locations within a molecule. As the molecule contains two opposite charges, it is electrically neutral. The term zwitterion is derived from the German word zwitter, meaning a hybrid, hermaphrodite. Zwitterions can be formed from compounds that contain both acid groups and base groups in their molecules (ampholytes).

All of the common amino acids found in proteins are ampholytes because they contain a carboxyl group (-COOH) that acts as an acid and an amino group (-NH₂) that acts as a base. In the solid state, amino acids exist in the dipolar or zwitterion form. If acid is added to a solution containing the zwitterion, the carboxylate group captures a hydrogen (H⁺) ion, and the amino acid becomes positively charged. If base is added, ion removal of the H⁺ ion from the amino group of the zwitterion produces a negatively charged amino acid.

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.

Chitin    →   Hitin

Chitin is a nitrogen-containing linear polysaccharide of ß(1->4) linked units of N-acetyl-ß-d-glucosamine. The structure of chitin is similar to cellulose except for the replacement hydroxyl group (-OH) at the carbon 2 with an acetyl amine group (–NH–CO–CH3). Chitin is the main component of the exoskeleton, or outer covering of insects, crustaceans, and arachnids. It is also found in the cell walls of certain fungi and algae. After cellulose, chitin is the second most abundant biopolymer in nature. It is insoluble in water, organic solvents, weak acids and lyes.