Quiz7 - Answer Key Post‐lab Quiz First Week of Co‐Ni...

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Unformatted text preview: Answer Key Post‐lab Quiz First Week of Co‐Ni Lab Chemistry 223 Fall, 2010 1. Why was it necessary to pour the column all at once rather than pouring small amounts of stationary phase into the column in increments? (1) This prevents column cracking. Cracks would allow analyte through the column without separation, defeating the purpose of doing chromatography. 2. If, instead of keeping the liquid/mobile phase and sample as just a thin layer at the top of the column you added the sample to the column when there was a 2 cm layer of mobile phase at the top of the column, what problem would you expect to have? (1) The peak would be broadened, so separation would take longer and the sample would end up more dilute than it should. 3. You test the initial effluent with dimethylglyoxime. What reaction gave rise to the red color (1) and why was it important that that red color not appear before you switched to 4 M HCl? (1) 2 DMG + Ni2+ → Ni(DMG)2↓+ 2 H+. When the red precipitate does not form, all the Ni2+ has been washed from the column, so separation is complete. 4. You tested the last effluent with thiocyanate. What reaction gave rise to the blue color? (1) Co2+ + SCN‐ → CoSCN+. ...
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This note was uploaded on 01/06/2011 for the course CHEM 223 taught by Professor Scheeline during the Fall '08 term at University of Illinois at Urbana–Champaign.

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