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Solution: Qualitative analysis. A flowchart showing a common scheme for identifying cations.If a solution contained a mixture of Ag+ and Al3+ ions, would this separation scheme work?

Problem

Qualitative analysis. A flowchart showing a common scheme for identifying cations.

A flowchart shows how to identify cations through qualitative analysis. The flowchart is presented here as an ordered list. Begin with a solution containing unknown metal cations: Add 6 molar HCl. Precipitate: Group 1 (insoluble chlorides: AgCl, PbCl2, Hg2Cl2). Precipitate: Group 1 (insoluble chlorides: AgCl, PbCl2, Hg2Cl2). Add H2S and 0.2 molar HCl. Precipitate: Group 2 (acid-insoluble sulfides: CuS, CdS, Bi2S3, PbS, HgS, As2S3, Sb2S3, SnS2). Decantate: remaining cations. Add (NH4) 2S at pH equals 8. Precipitate: Group 3 (base-insoluble sulfides and hydroxides: Al(OH) 3, Fe(OH)3, Cr(OH)3, ZnS, NiS, MnS, CoS). Decantate: remaining cations. Add (NH4)2HPO4 and NH3. Precipitate: Group 4 (Insoluble phosphates: Ca3 (PO4)2, Sr2 (PO4)2, Ba3(PO4)2, MgNH4PO4. Decantate: Group 5 (Alkali metal ions and NH4+).

If a solution contained a mixture of Ag+ and Al3+ ions, would this separation scheme work?

Solution

We are asked if this separation scheme would work if solution contained mixture of Ag+ and Al3+ ions.


Cations are positively charged ions. The cations in the solution can be separated by precipitating one out. 

We will refer to the solubility rules in order to determine if the scheme work to separate Ag+ and Al3+ ions in a mixture.


Solubility Rules:

Soluble Ionic Compounds:

 Group 1A ions (Li+, Na+, K+, etc.) and Ammonium ion (NH4+) are soluble
Nitrates (NO3-), Acetates (CH3COO- or C2H3O2-), and most Perchlorates (ClO4-) are soluble
Cl-, Br-, and I- are soluble except when paired with Ag+, Pb2+, Cu+, Hg22+
Sulfates (SO42-) are soluble except those of Ca2+, Sr2+, Ba2+, Ag+, and Pb2+

• Insoluble Ionic Compounds:

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