Problem: Qualitative analysis. A flowchart showing a common scheme for identifying cations. After which step would the first precipitate be observed?

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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+).

After which step would the first precipitate be observed?

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