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Qualitative inorganic analysis

Group I: the insoluble chlorides. Add 1 - 2 M HCl. AgCl, Hg 2 Cl 2 and PbCl 2 precipitate. Qualitative inorganic analysis. If stronger HCl is used, Pb may re-dissolve as the complex cation PbCl 4 –. Distinguishing between them: PbCl 2 is quite soluble in hot water.

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Qualitative inorganic analysis

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  1. Group I: the insoluble chlorides. • Add 1 - 2 M HCl. AgCl, Hg2Cl2 and PbCl2 precipitate. Qualitative inorganic analysis • If stronger HCl is used, Pb may re-dissolve as the complex cation PbCl4– • Distinguishing between them: PbCl2 is quite soluble in hot water. • AgCl is soluble in ammonia — the chloride of the complex cation Ag(NH3)2+ is soluble. • Hg2Cl2 precipitate turns black in the presence of ammonia. • PbCl2 is not that insoluble; at 1 M Cl–, 16 µM Pb2+ feeds through to group 2 CHEM 114 Fundamental Chemistry • If results are ambiguous, test for Pb2+ with chromate • Group I ppt. • Test for Pb • Test for Hg

  2. [Ag(NH3)2 +] K = [Ag+] [NH3]2 AgCl(s) ⇌ Ag+ (aq.) + Cl– (aq.) Ka = 1.8 × 10–10 Ag+ (aq.) + 2 NH3 (aq.) ⇌ Ag(NH3)2 + (aq.) K = 1.6 × 107 Complex ion equilibria Let [NH3] = 1 M; then [Ag(NH3)2 +]/[Ag+] = 1.6 × 107 If [Ag(NH3)2 +] = 0.1 M, then [Ag+] = 6.25 × 10–9 M To precipitate, [Cl–] = 0.3 M Let [NH3] = 2 M; then [Ag(NH3)2 +]/[Ag+] = 4 × 108 If [Ag(NH3)2 +] = 0.1 M, then [Ag+] = 2.5 × 10–10 M To precipitate, [Cl–] = 1.3 M CHEM 114 Fundamental Chemistry

  3. Complex ion equilibria CHEM 114 Fundamental Chemistry

  4. Complex ion equilibria CHEM 114 Fundamental Chemistry

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