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Group III Cation Flow Chart

Group III Cation Flow Chart. Al 3+ , Cr 3+ , Fe 3+ , Ni 2+. Source of OH -. ( SKIP STEP 1). NaOH (aq) (excess) NaOCl (aq) [NaClO (aq) ] NH 3 (aq). Oxidizes Cr 3+ (cation) to CrO 4 2- (anion; can’t ppt with OH - !). (STEP 2). Ppt (solid): Fe(OH) 3 (s) , reddish brown (dark)

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Group III Cation Flow Chart

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  1. Group III Cation Flow Chart Al3+, Cr3+, Fe3+, Ni2+ Source of OH- (SKIP STEP 1) NaOH(aq) (excess) NaOCl(aq) [NaClO(aq)] NH3(aq) Oxidizes Cr3+ (cation) to CrO42- (anion; can’t ppt with OH-!) (STEP 2) Ppt (solid): Fe(OH)3(s), reddish brown (dark) Ni(OH)2(s), pale green (light) Solution: CrO42-(aq), yellow Al(OH)4-(aq), colorless HC2H3O2(aq) NH3(aq), until just basic HNO3(aq) NH3(aq) (excess is fine—add away!) (STEP 6) (STEP 3) Ppt (solid): Fe(OH)3(s), rust colored, floating Solution: Ni(NH3)62+(aq), blue (may be faint) Ppt (solid): Al(OH)3(s), white, floating, gelatinous Solution: CrO42-(aq), yellow BaCl2(aq) (STEP 5a) DMG(aq) HCl (aq) KSCN(aq) (SKIP STEP 4) (STEP 8) (STEP 7) Ppt (solid): BaCrO4(s), yellow-white FeSCN(aq), dark, blood red solution Ni(DMG)2(s), vibrant red (“hot pink”) ppt (SKIP STEP 5b)

  2. Reminders • I will provide you 1 mL of the “known” solution (mixture of all three cations) • Do the known and unknown mixtures in parallel (critical to save time!). BUT… • Make sure to label all tubes and don’t throw away tubes until you are positive you don’t need them! • Follow the detailed instructions for each step (except parts I said to skip!) • **(typo) In Step 2, bottom, add HNO3 instead of H2SO4 • In Step 3, you probably won’t have to “transfer sol’n to a 50-mL beaker and…”. This is ONLY if your Vsol’n > ~3 mL • Remember to stir all solutions (particularly when adjusting pH) • Be very careful to not mix up “solution” with “precipitate” when carrying out procedures (“To the solution, add…”)

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