CHEMISTRY GLOSSARY

supersaturated solution    →   prezasićena otopina

Solution is supersaturated when it contains greater quantity of dissolved substance in itself than it corresponds to solubility of that substance at that temperature. It is said to be in an unstable state, and by shaking the vessel containing that such a solution separation of salt surplus can occur.

unsaturated solution    →   nezasićena otopina

Unsaturated solution is a solution that contains less than the maximum possible equilibrium concentration of a solute.

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.

saturated solution    →   zasićena otopina

Saturated solution is a solution that holds the maximum possible amount of dissolved material. When saturated, the rate of dissolving solid and that of recrystallisation solid are the same, and a condition of equilibrium is reached. The amount of material in solution varies with temperature; cold solutions can hold less dissolved solid material than hot solutions. Gases are more soluble in cold liquids than in hot liquids.

solid solution    →   čvrste otopine

Solid solution is a crystalline material that is a mixture of two or more components, with ions, atoms, or molecules of one component replacing some of the ions, atoms of the other component in its normal crystal lattice.

ionic strength    →   ionska jakost otopine

Ionic strength (μ or I) is a measure of the total concentration of ions in a solution, defined by

where z_i is the charge of ionic species i and c_i is its concentration.

solution composition    →   sastav otopine

Solutions are homogenous mixtures of several components. The component which is found in a greater quantity is called the solvent and the other components are called solutes. Quantitative composition of a solution can be expressed by concentration (amount, mass, volume and number), by fraction (amount, mass, and volume), ratio (amount, mass, and volume) and by molality. Amount, mass, and volume ratio are numerical, nondimensional units and are frequently expressed as percentage (% = 1/100), promile (‰ = 1/1000) or parts per million (ppm = 1/1 000 000). If it is not defined, it is always related to the mass ratio.

absorbance    →   apsorbancija

Absorbance (A) is a logarithm of the ratio of incident radiant power (P_o) to transmitted radiant power (P) through a sample (excluding the effects on cell walls).

The absorption of light by a substance in a solution can be described mathematically by the Beer-Lambert law

where A is the absorbance at a given wavelength of light, ε is the molar absorbtivity or extinction coefficient (L mol^-1 cm^-1), unique to each molecule and varying with wavelength, b is the length of light path through the sample (cm), and c is the concentration of the compound in solution (mol L^-1).

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).

activity    →   aktivitet

Activity (a) is a thermodynamic function used in place of concentration in equilibrium constants for reactions involving nonideal gases and solutions. For the species i activity is defined as

where a_i is the activity of the species i, c_i is its molar concentration, and f_i is a dimensionless quantity called the activity coefficient.