Presentation1qualonefirsdttryyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyy carpenter sy
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    Presentation1qualonefirsdttryyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyy carpenter sy Presentation1qualonefirsdttryyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyy carpenter sy Presentation Transcript

    • Separate /save some unknown • DR ROB’S “Get to the point of this lab!” • Worksheet • Postive cations like Pb2+ , Ag + and Hg+ • Can be ptt by OH-, Cr2O72-, S2- • And Cl-
    • Pb2+ Cr2O72-
    • . • The most confusing ion is the S2- ion • In acidic and in basic solutiopn • Chemlab sheet • Centiguge sheet
    • Best website • http://www.dartmouth.edu/~chemlab/chem3 -5/qual_cat/full_text/procedure.html
    • . • FROM BOOK RIGHT TO ADEMDUM • MENTION 12 IONS • YOU WILL DO THREE TODAY • DO ADDEMDUM FIRST • THEN GO TO BOOK • REVIEW CENTRIFUGE
    • . • EASY FOR SOMETHING TO OCCUR DURING THESE LABS • MUST PLAN BEFORE YOU GET HERE • USE OR LAB BOOK TO WRITE DOWN REACTIONS-MANY TESTSTUBES ALL AT ONCE!
    • . #1 – Qualitative Analysis • Principles of Qualitative Analysis 1.Confirmatory Tests: These are tests that determine conclusively that a certain ion is present. Interfering ions are removed before a confirmatory test is done. • .
    • . Separations: These are procedures that separate groups of ions from other groups, or individual ions in a mixture of ions. Separations are followed by confirmatory tests to identify the separated ion.
    • Precipitation and Separation of Group I Cations: • Group 1: The silver group: Ag+, Hg22+, Pb2+ -----These ions precipitate (as the chlorides) from 0.3M HCl solution. • « » »Rationale: Softest acids>>>>>>>> • react strongly enough with a borderline base • to precipitate in acid solution..
    • You know some of this already • You have already done lead in CHM121 • And, • You have just done another ion similar to Ni– which will get to shorty (Cu(NH3)4)
    • Just add hot water These cations are Pb+2, Hg2 • +2, and Ag+ are all insoluble in cold water.
    • Precipitation and Separation of Group I Cations: • Precipitation and Separation of Group I Cations: • Pb+2, Hg2+2, and Ag+ are all insoluble in cold water. • They can be removed as a group from solution by the addition of HCl via simple precipitation: Ag+ + Cl- → AgCl(s)
    • chloro-complexes may form !! • It is important to add enough HCl to ensure complete precipitation, but not too large an excess. In highly concentrated HCl solutions, chloro-complexes may form such as • AgCl2-1.
    • Precipitation and Separation of Group I Cations: • Lead chloride can be separated from AgCl and Hg2Cl2 by heating with water, essentially reversing the above reaction. • Once Pb+2 is in solution, you can discern its presence by adding chromate ion to produce a yellow solid: • Pb+2 + CrO4-2 → PbCrO4(s) (yellow)
    • Begin . . . . . . • Show the PDF • Show the word files • Show flow chart now
    • Precipitation and Separation of Group I Cations: • Hg2Cl2 can be distinguished from AgCl by reaction with ammonia via oxidation reduction to yield finely divided black metallic mercury and a white complex compound HgNH2Cl. As the reaction proceeds, the solid appears to change colors from white to black or gray:
    • . • Hg2Cl2(white solid) + 2 NH3(aq) → • NH4+(aq) + Cl-(aq) + Hg(black liquid) + HgNH2Cl(white solid)
    • Hg2Cl2(white solid) + 2 NH3(aq) → NH4+(aq) + Cl-(aq) + Hg(black liquid) + HgNH2Cl(white solid)
    • Aminomercuric chloride and,
    • • Silver chloride also reacts with aqueous ammonia to form a complex ion that remains in solution. Addition of a • strong acid will destroy the complex and confirm the presence of silver ion by re- precipitating the white AgCl solid:
    • • Silver chloride also reacts with aqueous ammonia to form a complex ion that remains in solution. Addition of a • strong acid will destroy the complex and confirm the presence of silver ion by re-precipitatin the white AgCl solid: • AgCl(s) + 2 NH3(aq) → Ag(NH3)2 +(aq) + Cl-(aq) • Ag(NH3)2+(aq) + 2 H+(aq)+ Cl-(aq) → AgCl(s) + 2 NH4aq)