Slide 1

Slide 2 Electrolysis of water 2H 2 O2H 2 + O 2 We consider water cleared by distillation several times as a chemically clear material. Water can be separated into two different kinds of gas with the help of Hoffman device. The important characteristic feature of electrolysis is that less gas is always gathered above the positive pole tube. Gasses developed on both poles are colourless, and if we smelled we wouldnt feel differences between them: both are inodorous. With our organs of sense we cannot recognize any differences between their physical features. If we examined other physical characteristics we would sense differences. If we filled balloons with them the one on the positive pole filled with oxygen would descend the other one filled with hydrogen - would rise up. Hoffmanns Electrolysis device Slide 3 Water is a molecular dipole We call a molecule dipole, when it has polar chemical bonds and the arrangement of them is asymmetric. The dispersion of charges inside the molecule is determining. H + H O H + H O H : H +.. O :: O.. Slide 4 Slide 5 Dissolving in water sugar and salt dissolve in water because they are molecular dipole for heat the process becomes quicker oil and iodine do not dissolve in water because they are nonpolar molecules Slide 6 In thermodynamics, the term exothermic describes a process or reaction that releases energy from the system, usually in the form of heat. After an exothermic reaction, more energy has been released to the surroundings than was absorbed to initiate and maintain the reaction. A part of the inner energy of the system becomes heat. Exothermic reactions the dissolving of washing powder the dissolving of domestic hydrochloride acid Slide 7 Endothermic reactions In thermodynamics, the term endothermic describes a process or reaction in which the system absorbs energy from its surroundings in the form of heat. Because of this the surrounding loses heat. So heat energy goes from the surrounding to the system. The absorbed heat changes into the inner energy of the system so it gets into a higher, more instable energy condition. Slide 8 The dissolving of potassium nitrate KNO 3 + H 2 O = K(aq) + NO 3 -(aq) + H 2 O Needed equipments: test-tube, a spoon Needed materials: potassium nitrate, water Description: We put a thermometer in a glass of water and pour some potassium nitrate into it. While it is dissolving the temperature of the water is decreasing. For the dissolving of potassium nitrate energy is needed which is absorbed from the surrounding. It is indicated by the temperature decrease of the solution. Slide 9 The molecule of the water is polar so it is a good dissolving material of many ion compounds like salt (NaCl). In water molecule oxygen has negative, hydrogen has positive charges. NaOH(dissolved in water) + HCl(dissolved in water) NaCl(dissolved in water) + H 2 O(fluid) HCl + H 2 O=H 3 O + + Cl - oxonium ion chloride ion Lye and acids also dissolve in water Slide 10 Amphoteric process In chemistry, an amphoteric species is a molecule or ion that can react as an acid as well as a base. Amphoteric molecules can either donate or accept a proton If water accept a proton it is called oxonium ion, if it donate a proton it is called hydroxide ion.