Experiment 7 Periodic Table Background: Elements are arranged on the Periodic Table in rows and columns in order of increasing atomic number (the atomic number is equal to the number of protons in the nucleus). There are seven rows called periods and eighteen columns called groups. The periodic recurrence of similar properties is the basis for arranging elements into groups. For example, elements in the same group on the periodic table form ions of the same charge because elements in a given group contain the same number of valence electrons (the outermost, highest energy electrons). The charge of the ions is one of the factors that contribute to the solubility of an ionic compound in water. As a consequence, different compounds tend to have similar water solubility when they contain ions from the same group on the periodic table. Water soluble ionic compounds are strong electrolytes (compounds that fully dissociate For example, a beaker containing aqueous sodium chloride, NaCl(ag), is actually a beaker that contains dissociated Na*(ag) cations and Cl-(ag) anions in a 1:1 mole ratio (mole ratios of dissociated ions are based on the subscripts of the ionic formula). into ions when dissolved). soluble ionic compounds are fully dissociated NaCl(aq) Na*(aq) + Cl-(aq) Some ions essentially always form soluble salts (a salt is another term for an ionic compound). These ions are known as spectator ions because they will never form an insoluble solid when mixed with other ions (an insoluble solid formed by mixing solutions is called a precipitate). Two examples of spectator ions are the nitrate anion, N0;,, and the ammonium cation, NH,+. The data from today's experiment will allow you to determine additional spectator ions. In part A of this experiment you will test the solubility of compounds that contain representative group 1, 2 and 17 ions by mixing ammonium or nitrate salts of these test ions sequentially with the silver cation, the carbonate anion and then the phosphate anion. The spectator ions ammonium and nitrate are used so that we can test the solubility of compounds that contain their oppositely charged counterpart. In part B of the experiment the reactivity of selected metals with water or hydrochloric acid will be observed. While nonmetal elements tend to be more reactive up and to the right of the periodic table (towards fluorine), metal elements tend to be more reactive down and to the left of the periodic table (towards francium). Laboratory Report – Periodic Table Type Name Here: Part A 1. Place 9 clean small test tubes in a test tube rack. The test tubes should be clean but do not have to be dry because aqueous solutions will be used. 2. To each test tube add 5 drops of the solution (0.1 M) indicated in the data table. 3. Next add 5 drops of silver nitrate (0.5 M) to each of the 9 test tubes. If there is no apparent change be sure to gently swirl the test tube to mix the reagents (a stirring rod can be used). If the contents of the test tube are cloudy, a solid precipitate was formed. If the contents of the test tube are clear, no reaction occurred. Record the results in the data table writing "ppt" and their color for precipitates and "NR" for no reaction. 4. Your instructor will inform you of where to dispose of the chemicals used. Rinse the test tubes and repeat the procedure two more times first using ammonium carbonate (0.5 M) in step 3 and then again using sodium phosphate (0.5 M) in step 3. Tes t Solution Test Ag+ CO32- РОз- Tube Ion Barium nitrate Ba2+ White ppt White ppt A m m oniu m chloride 2 Cl- White ppt 3 Calcium nitrate Ca2+ White ppt White ppt 4 Lithium nitrate Li+ Ammonium iodide I- Yellowish ppt Potassium nitrate K+ Sodium nitrate Na+ Strontium nitrate Sr2+ White ppt White ppt A m m oni u m bromide Br Off-White ppt