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Chemistry LibreTexts

Q-1 Analysis

  • Page ID
    150652
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    INTRODUCTION

    In this experiment, students will begin the qualitative analysis of unknowns. Today the Q-1 ion scheme will be performed. First, an analysis of a known solution will be carried out. After this, an unknown solution from the professor will be tested. Prior to lab, be sure to have specified numbers of copies of the Q-1 skeleton flow chart copied into the laboratory notebook as discussed in the background instructions for qual labs.

    The objective of this experiment is to observe the steps in the separation and identification of the cations Ag+(aq) , Bi3+(aq) and Pb2+(aq)in the known and unknown.

    On this website, there will only be the positive results of the known solutions. Therefore, you should use this page only as a guide to making connections between what you are observing and what is actually happening in the test tube. For detailed steps, follow your lab manual.


    Positive Results

    2.1: Lead / Pb+

    s1 Pb positive q1.png

    The formation of a yellow precipitate, PbCrO4(s), confirms the presence of lead. Centrifuging may help with the identification of the lead precipitate because the liquid phase is orange.

     

     

     

     

     

     

     

     

    2.2: Silver / Ag+

    s2 Ag q1.png

    A white precipitate of AgCl(s) confirms the presence of silver.

    Note: The silver-ammonia complex ion is destroyed by acid, and the released Ag+precipitates with the Cl- already in solution to form a definitive white solid.

     

     

     

     

     

     

     

    2.3: Bismuth / Bi3+ Confirmation 1

    s3 Bi1 q1.pngIf the sample contains bismuth, the formation of white cloudiness after about one minute is caused by the precipitation of BiOCl(s).

    Note: The presence of bismuth must be confirmed by both the test with water and the black precipitate formed with SnCl2(s). A negative result for the water test and a positive result for the SnCl2 test does not confirm the presence of bismuth.

     

     

     

     

     

     

    2.4: Bismuth / Bi3+ Confirmation 2

    For a second confirmation of bismuth, place some drops of the decantate in a test tube, add NaOH(aq) until the solution is definitely basic; a white to yellow precipitate is Bi(OH)3(s). To this mixture add few drops of SnCl2(aq) and stir; if bismuth is present, it will be reduced to black metallic bismuth.

    Note: The presence of bismuth must be confirmed by both the test with water and the black precipitate formed with SnCl2(s). A negative result for the water test and a positive result for the SnCl2 test does not confirm the presence of bismuth.

     

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