Group I Qualitative Analysis

Transcription

1 Group I Analysis Page 1 Illinois Central College CHEMISTRY 132 Laboratory Section: Group I Qualitative Analysis Name: Equipment 1-tray of dropper bottles 2-micro spatulas 2-wooden test tube blocks 4-medicine droppers micro test tubes 2-micro test tube brushes 2-10 ml beakers 1-small graduated cylinder Make labels for 6 dropper bottles and fill them with the following solutions: 6 M HCl 6 M NaOH 6 M HNO 3 6 M NH 4 OH 6 M HC 2 H 3 O 2 distilled water Make 6-8 capillary droppers and 2-3 stirring rods. Helpful tips Centrifuge In order to facilitate the separation of solid precipitate from supernatant liquid, a sample must be centrifuged. For the centrifuge to spin smoothly, it must be balanced. Be sure to place a like test tube with approximately the same amount of liquid just opposite your sample tube. Complete Precipitation When instructions require that a solution be made alkailne or acidic (in order to precipitate selected ions), be sure that you've added enough acid or base by swabbing a drop of the solution across a strip of litmus paper. Litmus turns blue when exposed to basic solutions and red when exposed to acidic solutions. Then THROW THE LITMUS PAPER AWAY. Drop Size It should be noted that the drops delivered by a cpillary pipette are much smaller than a medicine dropper. When instructed to add a given number of drops of unknown or a necessary reagent, be sure to use a medicine dropper for big healthy drops. Saftey Precautions Some unknowns contain solutions that may stain the skin. Treat them with care. The concentrated acids and bases will naturally cause skin irritations or burns, so if you should contact them, wash the solution off immediately.

2 Group I Analysis Page 2 Directions for Separation of Group I Cations Start with a mixture of 5 drops each of Ag +1, Hg +1, and Pb +2 solutions (or about 10 drops of your unknown solution). Add 3-4 drops of 6 M HCl, mix thoroughly with a stirring rod, and centrifuge. Test for completeness of precipitation by adding another drop of 6 M HCl to the supernatant liquid. Centrifuge again, if necessary, and remove the clear liquid with a capillary pipette. (This liquid filtrate can be discarded) Wash the precipitate (residue) remaining in the test tube with 10 drops of cold distilled water containing 1 drop of 6 M HCl. Centrifuge and discard the wash water. solid liquid Residue A White precipitate. May contain AgCl, Pb, Hg 2. Add 10 drops distilled water and, with stirring, about 3 minutes in a boiling water bath. Centrfuge quickly and immediately remove the clear liquid with a capillary pipette and place this "filtrate" liquid in another tube. (For more complete precipitation of the Pb +2, the hot water treatment can be repeated and the two liquid portions combined.) Filtrate A Contains any Group II-V cations that may be present. This can be discarded. solid liquid May contain AgCl and/or Hg 2 Residue B (This residue may be washed again with hot distilled water to remove any excess Pb +2.) Add 10 drops of 6 M NH 4 OH and mix thoroughly with a stirring rod. (At this point, check the solution for alkalinity with litmus paper and add more NH 4 OH if necessary.) Centrifuge the mixture. May contain Pb +2 Filtrate B Add 4 drops of K 2 CrO 4 solution and mix. Formation of a bright yellow precipitate confirms the presence of Pb +2 in your unknown. solid liquid Residue C May contain HgNH 2 Cl and HgO. If this black residue is present, this confirms the presence og Hg +1 in your unknown. May contain Ag(NH 3 ) 2 +1 Filtrate C Add 6 M HNO3 with stirring until the solution is definitely acidic. (Check this with litmus paper by removing a drop with a stirring rod and streaking a piece of blue litmus paper.) The formation of a white precipitate confirms the presence of Ag +1 in your unknown.

3 Group I Analysis Page 3 Equations for Group I Silver, Ag +1 Ag +1 + Cl -1 AgCl (white) AgCl + 2 NH 3 Ag(NH 3 ) Cl -1 Ag(NH 3 ) Cl HNO 3 2 NH 4 NO 3 + AgCl (white) Lead, Pb +2 Pb Cl -1 Pb (white) Pb Pb Cl -1 Pb +2 + CrO 4-2 PbCrO 4 (yellow) Mercury, Hg +1 or Hg 2 +2 Hg Cl -1 Hg 2 (white) Hg NH 3 NH 4 Cl + HgNH 2 Cl + Hg (gark grey)

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5 Group I Analysis Page 5 Illinois Central College CHEMISTRY 132 Laboratory Section: Name: REPORT SHEET Analysis of Unknown-Group I 1. Reagent Added Result Conclusion Unknown Number Ions Present in Unknown

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