The Experimental Procedure is writen for a single reference solution. If you are

Question

The Experimental Procedure is writen for a single reference solution. If you are simul. taneously identifying cations in borh a reference solution and a test solution, adjust the A. Separation of from Zn* and Al procedure accordingly. lf the test solution is a sample with an environ gly lf the test solution is a sample with an environmental o gravity filter 10-15 mL before beginning the Experimental Procedure Prepare the hot water bath for use in Parts A and D 1. Separa parate the hydroxide precipitates from the amphoteric hydroxides. To 2 mL of the reference solution (in a small test tube) add 10 drops of 6 M NaOH (Caution!) Test for complete precipita- (see Dry Lab 4.A). Centrifuge and save the precipitate tion (see Dry Lab 4.B) by adding several drops of 6 M NaOH to the supena atant supematant into a small test tube and save for Part D. ve the hydroxide precipitates. Dissolve the precipitate with a minimum number of drops of conc HNO,. (Caution: Be careful) If necessary, heat the sol ution in the hot water bath for several minutes. 1. Separate Fe from NI ions. To the solution from Part A.2, add -5 drops of 4 M NH,CI and then drops of conc NH, (Caution: Do not inhale-use a fume hood if available) until the solution is basic to pH paper: add an additional 2 drops of con B. Test for Iren(III) Ion NH, to ensure the complexing of the Ni. Centrifuge, save the precipitate. transfer the supernatant, to a small test tube for testing in Part C. and 2. Confirmatory test. Dissolve the precipitate with 6 M HCl and add -5 drops of 0.1 M NH,SCN. The blood-red solution due to the thiocyanatoron(III) complex confirms the presence of iron(III ion in the test solution. 1. Confirmatory test. To the supernatant solutior from Pärt B.L, add -3 drops of dimethylglyoxime solution. Appearance of a pink (brick-red) precipitate con C. Test for Nickel Ion firms the presence of nickel ion in the test solution. D. Test for Aluminum Ion 1. Separate Al* from Zn*. Acidify the supernatant from Part A. to pH papet with drops of 6 M HNO. Add drops of 6 M NH, until the solution is now basic to p paper; then add -5 more drops. Heat the solution in the hot water bath for several supernatant into a small test tube and save for the Zn2+ analysis in Part E. minutes to digest the gelatinous precipitate Centrifuge and decant tte To digest the precipiohe: to make the precipitole more compact 2. Confirmatory test. Wash the precipitate (see Dry Lab 4.C) wice with-1 mL of hot, deionized water and discard each washing. Centrifugation is necessary after each washing. Add drops of 6 M HNO, until the precipitate just dissolves. Add 2 drops of the aluminon teagent, stir, and add drops of 6 M NH, until the solution is again basic and a precipitate re-forms. Centrifuge the solution; if the Al(OH)s precipitate is now pink or red and the solution is colorless, then Al+ is present in the sample!9 t. Confirmatory test. To the supernatant from Part D.t, add drops of 6 M HCI mtil A very-light-green precipitate confirms the presence of Za** in the sample.ae Zine lon the solution is acid to pH paper; then add -3 drops of 0.2 M K,Ue(CNd stir. precipitate is slow to form and difficult to see. Centrifugation may be necessar Disposal Dispose of alt test. solutions and precipitates it the Was te Meto container. CLEANUP; Rinse each test tube twice with tap water. Discard each rinse m rinse twice with tap water andtwice with deionized water Waste Metaf Salts container. Thoroughly clean each test tube with soap and tap water The Next Step , The qualitative analysis of inorganic cations and anions is a study in itself, interest in she separatioin and identification of ions seems intriguing, research vn qualitative anilysis schemes online. Complete textbooks are also written on the subjecti-

Explanation / Answer

If instead of NH3 we add 6M NaOH then all of HCl will react and we will no longer have the required pH for the precipitation of the ions necessary. The addition of NH3 and NH4Cl ensures the right pH is available for the reaction to occur.

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