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Cards In This Set
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What glassware are recrystallizations usually done in?
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Erlenmeyer flasks and the size of the flask is determined by the volume used
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Why Erlenmeyer flasks?
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Good crystal growth, accompanied by expulsion of impurities requires space (depth) in solution
-This is achieved by Erlenmeyer flasks
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Why Erlenmeyer flasks?
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-Erlenmeyer flasks must contain much solution as possible (0.5 to 2/3 full) which is done by turning flask to 45 degree angle
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List 4 Reasons why Erlenmeyer flasks are idea
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1) Narrow neck allows some refluxing of the solvent so that surface evaporation is minimized (can put condenser on top of flask)
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List 4 Reasons why Erlenmeyer flasks are idea
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2) They can be corked or stoppered so that during crystallization vapour and liquid can equilbriate,
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List 4 Reasons why Erlenmeyer flasks are idea
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2)Thus the amount of solvent will not be changed through evaporation
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List 4 Reasons why Erlenmeyer flasks are idea
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3) They can be swirled to facilitate dissolving of the solid
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List 4 Reasons why Erlenmeyer flasks are idea
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4) It is easy to remove crystals from an erlenmeyer flask
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When setting up apparatus, the condenser is clamped to a bar. How tightly should the clamp hold the condenser
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Very loosely, as this is done to allow free swirling of the flask on top of the hotplate
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Why is swirling important in recrystallizations?
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It helps facilitate the dissolving of the solid and also prevents bumping which occurs during heating
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What do we place in the erlenmeyer flask initially?
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The pure solid, together with a boiling chip and a small amount of solvent is added at room temp to begin reflux, (not to fully dissolve)
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Once the mixture is heated to boiling what do we do?
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We add small amounts of solvent (via top of condenser) until the solid just dissolves
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Why do we add a minimum amount of solvent so that the compound just barely dissolves?
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This results in a solution that is saturated with the solid and when cooled should return the maximum amount of solute in the form of crystals
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When do we perform hot gravity filtrations?
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If either or both are present
1) Insoluble impurities remaining in the solution
2) Coloured, soluble impurities which necessitates the use of Norit
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How do we prepare for a hot filtration?
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Once desired compound has been dissolved in hot solvent, add an addition amount of solvent (1/4 of original volume to produce saturated solution)
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