Question

2+ [HCl,HNO3, Δ] (A.2) Numbers in refer to the Experimental Procedure. [A,H20] NaOH) [HNO3] (B.2) HNO3 [NaBiOsl (C.1) INH OH] (D.1) INH4OH [HCI] (D.2) H2DMG] (E) INH4SCN [HNO3](F.2) HCI(G) [aluminon,NH,OH [KFe(CN)d
Complete the following flow diagram for Qual II cations.

Answer 1

THE INSOLUBLE HYDROXIDES Group II- Al-3, Mn,Zn-^.Ni-^.Fe Zn and al [AKOH] and [Zn(OH) ] from the cation precipitates of Mn2, Nr2, Fe-3. A strong base added to a sohution containing the five cations form gelatinous hydroxides ofMn2, Nr, Fe but Zn2 and Al3 hydroxides are amphoteric and re- dissohve in excess base. The sohutions, [AKOH4] and [Zn(OH) ], are separated from the precipitates ofMn2, Ni2, Fe3 and analyzed. ummmum ions are separated as aqueous With the exception ofahuminum and zinc, the elements in this group are transition metals with incompletely filled d subshell This leads to a variety of oxidation states. Most of these elements have a great tendency to form colored complex ions. Careful observation of the color of the unknown solutions and of the colors produced along the way can provide useful chues m the identification of this group. But remember, colors can be misleading.

Group II Flow Chart Mn2, Ni-, Fe , Al3-, Zn2 A, H2O] NaOH Fe(OH) Ni(OH)2, Mn(OH) Zn(OHAIOH) HNO HNOl NaBio] NH NH Mno;Fe(OH), Ni(NH- AI(OH)s [HCI INH,SCNI FeNCS H,DMG] HNO HCI [aluminon.NH] K Fe(CN)lI Al(OH)aluminonKZn,[Fe(CN)

PROCEDURE Separation of zinc and aluminum from hydroxides precipitate 1. Add 1mL ofknown solution II into a qual tube and add 15 drops of 6 M NaOH. Centrifuge and test for completeness of precipitation Transfer the supermatant to another test tube with a Pasteur pipet. Save the supernatant for step 9 2. Wash the precipitate and discard the washing Dissolve the precipitate with a minimum amount of concentrated HNO3 Test for Mn2 Manganese ion is treated with sodium bismuthate, a strong oxidizer. The bismuthate ion, BiOj. oxidizes the Mn2 to the sohuble purple permanganate, Mn04. The color change may be fleeting but nevertheless confirms the presence ofMn2. 3. Transfer 5 drops ofthe solution from #2 into another qual tube save the remaining solution for step 5 4. To the 5 drops from step 3, add a scoopula tip full of NaBiO3. Note the appearance ofa purple color which sometimes can be fleeting This confirms the presence ofMn*2,

Separation and confirmation of Fe+ Iron cation is separated fiom the nickel cation with the addition of solutions of NH,Cl and NH. Fe3 forms a brown precipitate, Fe(OH) and a soluble bhue hexammine complex [NiNH)sl2 forms in solution. The Fe(OH)s precipitate is dissohved in acid and confirmed by the addition ofammonnum thiocyanate 5. 6. Transfer 12 drops from the soution saved from step 3. Add 5 drops of4 M NH4Cl and then drops ofconcentrated NHs until the solution has a pH of 10. Centrifige and separate the supematant from the precipitate. Save the supematant for step.8 7. Dissolve the precipitate with 6 M HCl and add the 6 drops of 0.1 MNHSCN. A blood red solution due to the thiocyanatoiron (III) complex confirms the presence of Fe*3

Confirmation of Ni'2 The confirmation of the nickel ion is the precipitation of the hexaamminenickel(I) complex,[Ni(NH)]2 wth dimethylgyoxime (DMG). strawberry red

8. Check to make sure that the pH is 8, iftoo basic add 6M HNO3 to the supenatant from step 6. Make sure that the pH is 8 and then add 5 drops of dimethylglyoxime. The appearance of a pink precipitate confirms the presence ofNr2 Separation of Al3 from Zn*2 The supernatant containing [AKOH)] and [Zn(OH)1 when acidified reforms aqueous Ar3 and Zn2. Ammonia is added to repreciptate Ar3 to ArO)swhile Zn forms the soluble tetraammine complex, [Zn(NH)]2 Al(OH)3) 3 NH4 H2O

Separation and Confirmation of Arr3 The adjustment of the pH of [AKOHto mild akaline produces precipitate, AOH)s, an opaque, gelatinous precipitate. The addition of the aluminon (ahumimum reagent) dyes the precipitate pink to red. 9. Acidify the supermatant fiom step 1 with 6 MHCl using a limus paper to ensure acidity. Add drops of 6 MNH until pH 8-9 is reached. 10. Heat in a boiling bath to digest the gelatinous precipitate. Centrifiuge and separate the supernatant and save for step 13.

11. Wash the precipitate twice with hot deionized water and discard the washings 12. Add 6 MHNO3 until the precipitate just dissolves. Add 5 drops of auminon and 3 MNH until the solution is pH 9. The presence ofa strawberry red precipitate indicat es the p resence of AF Confirmation of Zn2 When potassium hexacyanoferrate (II), KİFe(CN)] s added to an acidified solution of [Zn(NH)2, a light green precipitate of K ZnyFeo) forms, confirming the presence of Zn*2 2 K:Fe(CN)6] K2Zn[Fe(CN)6]2 e) 13. To the supernatant from step 10, add 1 MHCl until pH 4 is reached. Add 3 drops of 0.2 MM K2Fe(CN)s] and stir. A very light green precipitate that is slow to form confirms the presence of Zn*2. Centrifuging might be necessary to visualize the precipitate Unknown Determination of Group II Cations Repeat the experiment substituting your unknown for the Group II known The unknown can also be determined by running both the Group 1I known and unknown side by side