ANION ANALYSISMuch of the work you will be doing in the Chemistry 112 laboratory will be concerned with identifying positive and negative ions, that is, cations and anions, in solutions whose composition is unknown. This procedure is called QUALITATIVE ANALYSIS.The modern chemist frequently wishes to identify the constituents in a very small amount of substance, and so he depends heavily on instrumental meth-ods of analysis. While the procedures you will use do not use fancy and expen-sive instruments, your methods are still very effective in determining the major components of systems containing common inorganic ions. Because anion analysis is somewhat simpler than cation analysis, we shall begin our work in qualitative analysis with methods of identifying four common anions in solution: PO43-, phosphate Cl-, chloride SO42-, sulfate NO3-, nitrateAfter having determined the chemical reactions of the individual ions, you will be asked to identify the ions present in an unknown mixture. CHEMICAL REACTIONS OF INDIVIDUAL ANIONS 1. The BaCl2 TestTake a set of four small test tubes. After cleaning them, label them 1 through 4, and place 4-5 drops of one of the known solutions in each tube as follows:Test tube Known Solution1 PO43-, phosphate2 SO42-, sulfate3 Cl-, chloride4 NO3-, nitrateNext, make each solution slightly basic by adding 5 M ammonia (NH3) dropwise. Making sure the solution is thoroughly mixed, test the basicity of the solution with litmus paper as demonstrated by your instructor. When the solutions are basic, note any changes that have occurred, and enter your observations in your lab book. Next, add 2-3 drops of 0.2 M BaCl2 to form precipitates between Ba2+ and some of the anions. Ba2+(aqueous) + anion(aqueous) → [Ba(anion)](solid)Record observations on the color and texture or appearance of the pre-cipitates in your notebook. It is best to draw a table in your notebook some-thing like that below.Some of the precipitates you have formed will dissolve in acid. In each case where a precipitate has formed with BaCl2, make the solution acidic with 6 M HCl (blue litmus paper should turn red in acid). Be sure to mix the solu-tion well after adding acid! (The most common error made in qualitative analysis laboratory is to fail to mix solutions completely!) Record your observations. (If you had made a table as described above, you can add your observations on Chemistry 112: Anion Analysis Page 7Revised: December 2005Be sure to record the results of your tests in your notebook.To test for a basic solu-tion, use red litmus paper. It will turn blue if the solution basic. Just remember: blue = base.The ammonia bottle may be labeled either with the formula NH3 or, less cor-rectly, as NH4OH.acid solubility to this table.) Discard the solutions from the tests above and clean the test tubes thoroughly. 2. The AgNO3 TestOnce again prepare four test tubes, each containing 4-5 drops of one of the known solutions. Dilute each solution with about 1 mL of distilled water and then add 2 drops of silver nitrate, AgNO3, solution. Now you should see some of the anions combine with silver ion to again produce insoluble precipitates. Ag+(aq) + anion(aq) → [Ag(anion)](s)Once again record your observations in a table such as that suggested above. After observing the precipitates that may form with some anions, attempt to dissolve these precipitates in acid. This time, however, you must use nitric acid, HNO3, rather than hydrochloric acid, HCl. (Why?) Add 4 drops of 3 M HNO3 to each precipitate with silver ion, mix well, and note the results. Again record your observations in the table of results. 3. The Brown Ring Test For Nitrate Ion As you may have observed in your tests thus far, the nitrate ion does not form precipitates with either Ba2+ or Ag+. Therefore, we have to have some indepen-dent way of testing for the ion. The test that has been used for many years is called the brown ring test, and it is specific for NO3-. Place 10 drops of the solution to be tested in a clean, well-rinsed test tube. Make the solution acidic by adding 3 M H2SO4 as needed. Next, add 5 drops of a freshly prepared, saturated solution of iron(II) sulfate (FeSO4) and mix gently. Incline the test tube at a 45o angle, and, as shown in the sketch, carefully add 5 drops of concentrated H2SO4 so the drops roll down the side of the test tube and slide gently onto the top of the solu-tion. DO NOT MIX the solutions! Two separate liquid layers will be observed in the test tube. If NO3- is present, a very faint brown ring will be observed near the bottom of the test tube, thereby confirming the pres-ence of nitrate ion. Record your observations in your notebook. Chemistry 112: Anion Analysis Page 8Revised: December 2005 Anion PO43- SO42- NO3- Cl- Color and texture of precipitate Precipitates that dissolve in HClRemember to use blue litmus paper to test for acidity.Blue litmus paper turns red in acid solution.QUALITATIVE ANALYSIS OF AN UNKNOWN MIXTURE The goal of this experiment is to be able to analyze a solution that may con-tain a mixture of any or all of the following anions: PO43-, SO42-, NO3-, Cl-. Based on the tests you have done above, you should be able to work out a fool-proof scheme that will allow you to do this analysis. Therefore, at this point you should sit back for a moment, think about your results, and construct a scheme for the analysis of the unknown solution. As usual, you will find it helpful to construct a table, such as that below, to organize your results. Once you have worked out an approach to analyzing an unknown, it is always good to try it on a solution that you have made up yourself. For example, put a few drops of each of the known solutions of PO43-, NO3-, SO42-, and Cl- in a single test tube and see if your method of analysis will allow you to identify their presence unequivocally. When you are satisfied with your method of analysis, work up your courage and ask your instructor for an unknown. (He or she will want to see your notebook at this point to make certain you have been recording your tests and observations properly. The instructor may also ask you what method of analysis you have chosen.) Determine the anion content of your unknown in the remaining time of the laboratory period, being certain to write down all of your procedures and observations. Summarize your observations in a table, and then list the results as follows:Anions probably present: