CHEM 1&2 Lab Manual & worksheets pg 194

CHEM 1&2 Lab Manual & worksheets pg 194 -...

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Experiment 19: Qualitative Analysis General Chemistry I and II Lab Manual Dakota State University page 194 of 232 AgCl Ag(NH3)4+ Add Nitric Acid AgCl Add NH3 PbCrO4 Pb+2 Add K2CrO4 AgCl,PbCl2 Heat Groups II - IV Ag+, Pb+2, Groups II - IV Add HCl There are two principle issues that you will have to resolve when running these analyses. The first is “what does a positive test look like?” Some are obvious, some are more subtle; it is always very helpful to be able to see a positive to compare the unknown with. The second question is “how do I know it is not a contaminant?” To answer these questions, you will want two solutions in addition to the unknown; the standard, and the blank. Run all three samples (the standard, the blank and the unknown) simultaneously. Anything you do to one solution, do them to all solutions, and always remember to keep them separate. Many qualitative analysis schemes recommend running the standard, then repeating the procedure for the unknown. It is more efficient, and therefore faster, if you
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Unformatted text preview: can keep the solutions separate so you can run all three at the same time. Standard: The standard contains all possible ions for the entire procedure. To make it, add 5 drops of each ions nitrate into the same clean dry test tube (AgNO 3 , Pb(NO 3 ) 2 , Bi(NO 3 ) 3 , Cu(NO 3 ) 2 , Sn(NO 3 ) 4 , Ni(NO 3 ) 2 , Co(NO 3 ) 2 , Mn(NO 3 ) 2 , Al(NO 3 ) 3 , Cr(NO 3 ) 3 , Ba(NO 3 ) 2 , Ca(NO 3 ) 2 , and KNO 3 . Blank: The blank is the opposite of the standard; it contains NO ions. Use the appropriate volume of distilled water. If a positive ever appears in the blank, this is an indication that somewhere, the solutions picked up a contaminant, and you will want to re-run the tests to ensure that you have no false positives. Group I: Ag + and Pb +2 Group I ions (which traditionally include Hg +2 as well) are put together because they all have insoluble (or relatively insoluble) salts of chloride. This fact allows for easy separation of these ions (aside from lead, as its chloride is still partially...
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This note was uploaded on 01/27/2012 for the course CHM 2045 taught by Professor Josephwalter during the Fall '11 term at Dakota State.

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