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CHEM 1&2 Lab Manual & worksheets pg 199

CHEM 1&2 Lab Manual & worksheets pg 199 -...

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Experiment 19: Qualitative Analysis General Chemistry I and II Lab Manual Dakota State University page 199 of 232 Dissolve the precipitate from the above separation step using dilute HCl. Add several drops of aluminon reagent. If a precipitate forms, it is aluminum. Verification of Cr +3 : Add a LITTLE BIT of sodium bismuthate, Na 2 BiO 3 , to the decantate from above. A yellow color is verification of chromate. Group IV: These are the last of the ions that can be separated by their insoluble salts. Group IV includes Ba +2 and Ca +2 (and many qualitative analysis schemes include Sr +2 in this group as well). They are precipitated out as carbonates. Separation of Group IV from group V: Verify that the decantate from the separation step of group III is still alkaline; if it is not, add concentrated ammonium hydroxide until it is. Once alkaline, add 1 mL of ammonium carbonate; barium and calcium will precipitate out as carbonates. Centrifuge and decant. Once separated, dissolve the solid in hot dilute acetic acid.
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Unformatted text preview: Split the solution into two parts. Verification for Ba +2 : To one portion from the above step, add a few drops of potassium chromate. A precipitate, barium chromate, confirms the presence of barium. Verification of Calcium: To the other solution, add a few drops of sodium oxalate. The presence of a precipitate verifies calcium. Group V: Group V ions can be thought of as “everything left over.” We will assume this “group” contains only K + , although many qualitative analysis schemes include Na + , Mg +2 and NH 4 + as well. Flame test for K + : Take an iron loop and “clean” it by putting it into a hot flame until the loop glows red hot (be careful not to burn yourself). Allow the loop to cool, and dip it in the remaining decantate from the group IV separation step. Be sure a drop is on the wire. Put the drop into the flame; a red flame verifies potassium. Calculations:...
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