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Investigation 4 PERIODIC PROPERTIES (?)-THE PROPERTIES CHANGES OF ELEMENTS IN THE SAME GROUP ?Aim? To investigate the chemical properties changes of elements in the same period. ?Safety? 1. Wear safety goggles; 2. Do not touch Chlorine water and Bromine water by hand; 3. Do not smell Chlorine water and Bromine water directly by nose; 4. Be careful with flammability of cyclohexane and hexane. ?Chemicals? Iodine Fresh chlorine water Bromine water Aqueous sodium chloride Aqueous potassium bromide Aqueous potassium iodide Aqueous AgNO3 Distilled water Cyclohexane Ethanol I2-KI solution Starch solution ?Equipments? 6 test tubes 1 test tube rack 1 test surface 1 tweezers 3 universal indicator papers 1 pH meter ?Background? The halogens F, Cl, Br and I (At has not been included because of its scarcity and nuclear instability) are very reactive non-metals that occur in the penultimate group of the periodic table, hence they all require just one electron to complete their valence shell. All of the elements exists as diatomic molecules (F2, Cl2, Br2, I2) in which the atoms are joined by single covalent bonds. Going down a group of the periodic table, for successive elements there are more energy levels filled with electrons, so the outer electors are in higher energy levels and farther from the nucleus. ...read more.


Tests for halide ions: Halide ions (Cl-, Br- and I-) with silver ions: NaCl White precipitate is produced Darkens after it was placed in sunlight KBr Cream precipitate is produced. KI Yellow precipitate is produced. ?Data Analysis? 1) The solubility of iodine in different solvents: The solubility is larger in non-polar solvent (water, ethanol) and smaller in polar solvents.(cylohexane and KI) The purple color of iodine in cyclohexane is that because in non-polar solvents, iodine froms the violet solution. 2) Test iodine reacts with starch: According to the general knowledge we knew, the phenomenon of this reaction should be blue, but the color observed was black-green. That was because some of the starch hydrolysis in water and produced something could make the color darker. 3) Test the acid-base properties: 1. Cl2: The color of the universal indicator papers showed that Cl2 is strong acid. 2. Br2: The color of the universal indicator papers showed that Br2 is a kind of acid, but not very strong. 3. I2: The color of the universal indicator papers showed that I2 is a strong base. Actually, I2 is acid. The reason is that the original color of I2 is red-brown, that made us can't see the phenomenon clearly. ...read more.


This means that a higher halogen will displace a lower halogen from its salts. A lower halogen cannot displace a higher halogen from its salts. 4. When starch reacts with iodine, the typical blue black color will appear. That's a good way for us to identify starch and iodine. 5. After photodissociation, the color of some precipitates will change. will become black. That's the most obvious one. Other precipitates will become darken. ?Evaluation? 1. Because we use solid iodine in the first experiment. If we add the solvent into the test tube first, the test tube will be wet and the solid iodine we put in later will attach on the surface inside instead of fall into the liquid. For this reason we must add solid iodine first in experiment 1. 2. According to the first experiment, we found that the solubility of iodine in pure water is very low. But the solubility of iodine in potassium iodide solution is relatively much higher. So we use I2-KI solution to increase the amount of iodine in order to let the phenomenon more obvious. ?REFERENCE? 1) �Chemistry�(for use with the International Baccalaureate Diploma Programme) [3rd Edition] <John Green & Sadru Damji> First published in 2007 by IBID Press, Victoria, Page 77 to 78. 2) http://www.epa.gov/ttn/atw/hlthef/hexane.html 3) http://baike.baidu.com/view/373611.htm 4) http://baike.baidu.com/view/908645.htm ?? ?? ?? ?? 1 6 ...read more.

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