CHEMISTRY GLOSSARY

kilogram    →   kilogram

Kilogram (kg) is the SI base unit of mass; it is equal to the mass of the international prototype of the kilogram.

The prototype of the standard is a cylinder of platinum-iridium alloy (90:10), 39 mm in diameter and 39 mm high. Prototype of the kilogram kept by the Bureau International des Poids et Mesures (International Bureau of Weights and Measures) at Sèevres, near Paris.

Brinell hardness    →   Brinellova tvrdoća

Brinell hardness is a scale for measuring the hardness of metals introduced around 1900 by Swedish metallurgist Johan Brinell (1849-1925). A small chromium steel ball is pressed into the surface of the metal by a load of known weight. The loading force is in the range of 300 N to 30 000 N. The ratio of the mass of the load in kilograms to the area of the depression formed in square millimetres is the Brinell Hardness Number.

calorific value    →   kalorična vrijednost

Calorific value is the heat produced by a given weight of fuel on the completion of combustion; it is measured in kilojoules per kilogram (kJ/kg).

chlorinity    →   klorinitet

Originally chlorinity (symbol Cl) was defined as the weight of chlorine in grams per kilogram of seawater after the bromides and iodides had been replaced by chlorides. To make the definition independent of atomic weights, chlorinity is now defined as 0.3285233 times the weight of silver equivalent to all the halides.

The Mohr-Knudsen titration method served oceanographers for more than 60 years to determine salinity from chlorinity. This modification of the Mohr method uses special volumetric glassware calibrated directly in chlorinity units. The Mohr method uses potassium chromate (K₂CrO₄) as an indicator in the titration of chloride ions chloride (plus a small amount of bromide and iodide) with a silver nitrate (AgNO₃) standard solution.

The other halides present are similarly precipitated.

A problem in the Mohr titration was that silver nitrate is not well suited for a primary standard. The Danish physicist Martin Knudsen (1871-1949) suggested that a standard seawater (Eau de mer Normale or Copenhagen Normal Water) be created and distributed to oceanographic laboratories throughout the world. This water was then used to standardize the silver nitrate solutions. In this way all chlorinity determinations were referred to one and the same standard which gave great internal consistency.

The relationship between chlorinity Cl and salinity S as set forth in Knudsen's tables is

In 1962, however, a better expression for the relationship between total dissolved salts and chlorinity was found to be

gray    →   grej

Gray (Gy) is the SI derived unit of absorbed dose of radiation. The gray is the absorbed dose when the energy per unit mass imparted to matter by ionising radiation is one joule per kilogram (Gy = J/kg). The unit was named after the British scientist Louis Harold Gray (1905-1965).

international system of units    →   međunarodni sustav jedinica

International System of Units (SI) is the unit system adopted by the General Conference on Weights and Measures in 1960 and recommended for use in all scientific and technical fields. It consists of seven base units (meter, kilogram, second, ampere, kelvin, mole, candela), plus derived units and prefixes.

mass    →   masa

Mass (m) is the quantity of matter contained in a particle or body regardless of its location in the universe. Mass is constant, whereas weight is affected by the distance of a body from the centre of the Earth (or of other planet). The SI unit is kilogram.

According to the Einstein equation

all forms of energy possess a mass equivalent.

molality    →   molalitet

Molality or molal concentration (b; formerly m) is a concentration in which the amount of solute is stated in moles and the amount of solvent in kilograms.

The unit of molality is mol kg^-1.

newton    →   njutn

Newton (N) is the SI unit of force, being the force required to give a mass of one kilogram an acceleration of 1 m s^-2 (N = kg m s^-2). It was named after the British scientist Sir Isaac Newton (1642-1727).

precision balance    →   tehnička vaga

Precision balances typically display results from three to one decimal places (0.001 g up to 0.1 g). The readability precision balances are reduced when compared to analytical balances but, precision balances accommodate higher capacities (up to several kilograms). In its traditional form, it consists of a pivoted horizontal lever of equal length arms, called the beam, with a weighing pan, also called scale, suspended from each arm.

In electronic top pan, or toploader balances, mass is determined not by mechanical deflection but by electronically controlled compensation of an electric force. The signal generated enables the mass to be read from a digital display. The mass of the empty container can be stored in the balance’s computer memory and automatically deducted from the mass of the container plus its contents.