CHEMISTRY GLOSSARY

water    →   voda

Water (H₂O) (dihydrogen oxide) is a binary compound that occurs at room temperature as a clear colorless odorless tasteless liquid; freezes into ice below 0 °C and boils above 100 °C. Water is a chemical compound which is essential for living organisms and it is widely used as a solvent.

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.

water hardness    →   tvrdoća vode

Hardness is defined as the concentrations of calcium and magnesium ions expressed in terms of calcium carbonate. These minerals in water can cause some everyday problems. They react with soap and produce a deposit called soap curd that remains on the skin and clothes and, because it is insoluble and sticky, cannot be removed by rinsing.

Hard water may also shorten the life of plumbing and water heaters. When water containing calcium carbonate is heated, a hard scale is formed that can plug pipes and coat heating elements. Scale is also a poor heat conductor. With increased deposits on the unit, heat is not transmitted to the water fast enough and overheating of the metal causes failure. Build-up of deposits will also reduce the efficiency of the heating unit, increasing the cost of fuel.

There are two types of water hardness, temporary and permanent.

Temporary Hardness is due to the bicarbonate ion, HCO₃^-, being present in the water. This type of hardness can be removed by boiling the water to expel the CO₂, as indicated by the following equation:

Permanent hardness is due to calcium and magnesium nitrates, sulphates, and chlorides etc. This type of hardness cannot be eliminated by boiling.

water ion product    →   ionski produkt vode

Water ion product (K_w) is a concentration product of hydrogen and hydroxide ions. For the reaction:

the equilibrium expression would be:

Note that all pure liquid terms are omitted, hence H₂O does not appear in the denominator. At 25 °C, K_w = 1.0×10^-14 mol²dm^-6 = (K_a)(K_b)

Wilson’s chamber    →   Wilsonova komora

Wilson’s chamber is used for detection of radioactive radiation. Wilson’s chamber has a glass cylinder filled with air that has been saturated with water vapour. Radioactive radiation in its way ionises molecules of gas which then function as centres on which water vapour condenses into very small drops, thereupon showing Tyndall’s effect, i.e. is they are visible as a bright trail.

Winkler’s method    →   Winklerova metoda

Winkler’s method was once a common method used to determine the dissolved oxygen concentration by titration. Now rarely used due to the accuracy and low price of oxygen meters.

The water sample is first treated with excess manganese(II) sulfate solution and then with an alkaline solution of potassium iodide. The Mn(OH)₂ initially formed reacts with the dissolved oxygen. The amount of MnO(OH)₂ formed is determined by reaction with iodide ion in acidic solution. The iodine formed may be titrated against standard thiosulfate solution, using starch as an indicator.

wire mesh    →   azbestna mrežica

Wire mesh (wire gauze) is used for uniform distribution of flame heat in base of a heated body. It is made of a iron wire strands with or without ceramic interior cores.

Wohler’s synthesis    →   Wohlerova sinteza

Wöhler’s synthesis is a synthesis of urea performed by the German chemist Friedrich Wöhler (1800-1882) in 1828. He discovered that urea (CO(NH₂)₂) was formed when a solution of ammonium isocyanate (NH₄NCO) was evaporated. At the time it was believed that organic substances such as urea could only be made by living organisms, and its production from an inorganic compound was a notable discovery.

work    →   rad

Work is the energy required to move an object against an opposing force. Work is usually expressed as a force times a displacement.

When a constant force F acts on a point-like object while the object moves through a displacement s, the force does work W on the object. If force and displacement are at a constant angle Θ to each other, the work is expressed by the scalar product of these two vectors:

When the force F on a point-like object is not constant that is, it depends on the position of the object, the work done by force while object moves from initial position with coordinates (x_i, y_i, z_i) to final position with coordinates (x_f, y_f, z_f)is given by expression:

Where F_x, F_y and F_z are scalar components of the force.

SI unit for work is joule (J); 1 J = 1 Nm = 1 kg m² s^-2. The electron-volt (eV) is commonly used in atomic and nuclear physics.

X-ray diffraction    →   rendgenska difrakcija

The regular array of atoms in a crystal is a three-dimensional diffraction grating for short-wavelength waves such as X-rays. The atoms are arranged in planes with interplanar spacing d. Diffraction maxima occur in the incident direction of the wave, measured from the surface of a plane of atoms, and the wavelength λ of the radiation satisfy Braggs’s law: