Expt6b-07 - _University of Puget Sound Department of...

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Exploring the Periodic Table: Groups 1, 2 and 17-Week 2 1 _____University of Puget Sound Department of Chemistry Chem 110 E XP . 6–E XPLORING THE P ERIODIC T ABLE : G ROUPS 1, 2 AND 17-W EEK 2 © WEEK 2 In Week 1 the following procedures were performed to develop a scheme or method for identifying the cation part of a compound containing a group 1 or 2 ion. 1. A video will show the reactivity of the alkali metals (elements) with water and with oxygen. 2. (a) You will investigate the relative solubilities of the alkaline earth (Group 2) hydroxides: Mg(OH) 2 , Ca(OH) 2 , Sr(OH) 2 and Ba(OH) 2 . (Group 1 hydroxides are all very soluble.) (b) You will investigate the solubilities of various salts of Group 1 and 2 elements by mixing solutions containing Group 1 or 2 cations with solutions of selected anions from their sodium salts (phosphate, PO 4 3- ; molybdate, MoO 4 2- ; sulfate, SO 4 2- ; and chromate, CrO 4 2- ) and noting whether a precipitate forms. 3. You will perform flame tests on salts containing Group 1 and 2 metal ions. These ions often impart characteristic colors to the flame, due to the emission spectra of the excited metal atoms . In Week 2 a method for identifying the anions from group 17 will be developed and the identity of an unknown compound containing a group 1 or 2 cation and a group 17 anion will be determined using these methods. 4. You will carry out reactions which produce the halogen elements, Cl 2 , Br 2 and I 2 , respectively, and you will learn to recognize them by the characteristic colors they display in hexane solution. The colors of the halogens are then used as a basis for tests to determine if either bromide (Br - ) or iodide (I - ) ions are present in a salt. 5. You will apply the chemical knowledge gained in Parts 2-4 above to identify the cation and anion present in an unknown salt. The cation will be one of Li + , Na + , K + , Mg 2+ , Ca 2+ , Sr 2+ , Ba 2+ ; the anion will be one of the halide ions ; Cl - , Br - and I - .
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Exploring the Periodic Table: Groups 1, 2 and 17-Week 2 2 EXPERIMENTAL PROCEDURE - WEEK 2 BE SURE TO RECORD ALL OBSERVATIONS, AS YOU MAKE THEM, IN YOUR NOTEBOOK. PART 4. HOW TO TEST A SALT FOR THE PRESENCE OF GROUP 17 IONS; CHLORIDE ION, BROMIDE ION OR IODIDE ION. In this section you will generate the halogen elements chlorine (Cl 2 ), bromine (Br 2 ) and iodine (I 2 ) by oxidizing the respective halide ions (Group 17); Cl - , Br - and I - . The diatomic, non-polar halogen molecules have low solubility in water, but are readily soluble in hexane. By having a few drops of hexane present it is possible to obtain fairly concentrated solutions of the halogens, which enables them to be recognized by their characteristic colors. Whereas chloride, bromide and iodide ions are water soluble and colorless, and their presence cannot be established by simple visual inspection. Developing an Identification Scheme for the Group 17 Anions
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Expt6b-07 - _University of Puget Sound Department of...

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