LECTURE 4 Recrystallization 2011 SPRING - white bkg

LECTURE 4 Recrystallization 2011 SPRING - white bkg -...

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Click to edit Master subtitle style 4/27/11 Announcements An extension was granted on the deadline for the Safety Quiz. Please complete your Prelab Quizzes in a timely manner, and submit them fully. No further deadlines will be extended.
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4/27/11 Announcements Ø The midterm exam is at 7:00 PM on March 9. Locations are TBA- check Compass Ø If you have a conflict with the exam, email me now Ø The weeks of Feb 28 and March 7 we will not meet in the lab space. Check Compass for TBA locations Ø Remember to finish the recrystallization quiz Ø The recrystallization lab will take 2 weeks Ø The lab report for TLC is due the week of Feb 8 Ø Hot glass looks like cold glass
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Click to edit Master subtitle style 4/27/11 Recrystallization Laboratory 1
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4/27/11 What is recrystallization? General principles: Ø Compounds dissolve more easily in hot solvents Ø When crystals form, they tend to exclude impurities Purification technique for solids
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4/27/11 How to recrystallize 1. An impure solid is dissolved in an appropriate hot solvent 2. Solution is cooled causing crystals to form and impurities to stay in the solvent
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4/27/11 Solutions can become “Supersaturated” To induce crystallization – Ø Scratch the inside of flask with a glass stir rod Ø Further concentrate solution (evaporate solvent) Ø Cool solution in ice Ø Add a seed crystal Ø Be patient
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4/27/11 Finding the right solvent A good solvent will: 1. Not react with desired compound 2. When hot, dissolve a large amount of desired compound 3. When cold, dissolve as little of desired compound as possible 4. Be volatile
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4/27/11 What kinds of impurities exist? 1.
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This note was uploaded on 04/27/2011 for the course CHEM 233 taught by Professor Staff during the Spring '08 term at University of Illinois, Urbana Champaign.

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LECTURE 4 Recrystallization 2011 SPRING - white bkg -...

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