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27 Cards in this Set
- Front
- Back
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What makes a good recrystallization solvent? (5)
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1. favorable temp. coefficient: solute is essentially insoluble at room temperature or below, highly soluble at temps below solute melting point
2. Impurities insoluble in the solvent at all temps or remain soluble at room temperature 3. Low enough boiling point so easily evaporated from purified solute 4. BP lower than MP of the solute 5. solvent does not react with solute |
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How to assess general solubility of solute in a variety of solvents?
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"like dissolves like"
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Dielectric constants:
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2-3 non-polar, >10 polar
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Why should you limit the solvent used in recrystallization?
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it will limit recrysalization yield
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If too much dichloromethane is used in chromatography, what happens?
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it makes the solute mixture sufficiently polar to elute the fluorenone along with the fluorene
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In recrystallization, how are impurities removed?
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while kept hot, through gravity filtration
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How to predict the highest possible yield of recrystallization?
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use solubility at higher temp (mg/mL) to determine max amount that could dissolve. Then use solubility of same substance at the lower temperature. This is how much will recrystallize.
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Describe trimyristin.
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it's a tri-ester of 14-carbon saturated fatty acid (carboxylic), myristic acid, and glycerol (alcohol). It has three long non-polar tails but also a "head" portion composed of three polar carboxyl groups
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What solvents are used with the trimyristin and why?
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-diethyl ether to interact with non-polar tails
-solvent like dichloromethane is more polar and can interact with polar head group |
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If you have an organic acid like benzoic (4.2) in non-polar solvent like diethyl ether, you must add what to be ionized?
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the conjugate of a weaker acid (HCO3-, from carbonic acid 6.4)
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If you have benzoic acid and you deprotonate it, will it be soluble in water?
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yes
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Why must you vent the funnel in the base-base extraction?
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CO2 build up
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a mixture of two immiscible solvents can be separated using a separatory funnel because....
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the two liquids will for layers based on different density. in the case of water and diethyl ether, water is more dense
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once benzoate anion is separated, it can be reprotonated by adding HCl- a strong acid then...
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the non-ionic will precip out
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an organic alcohol can be deprotonated by a....
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a stronger base (naOH)
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in chromatography, how does the separation work?
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species of varying relative polarity moves across or through the stationary phase capable of interacting electrostatically with the more polar compound
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What are the polar "adsorbents" in the Chromotography?
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Al2O3 or silica gel (sio2; H2o)
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The more polar component in a mixture will "stick" to the adsorbent material until....
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a more polar solvent is available to vie for it
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less polar solutes will not
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adhere to the adsorbant, it wicks its way up the TLC plate or flows through a chromatography column
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less polar solutes have a ___Rf and are eluded _____
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larger, first
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on a TLC plate, a polar solvent will move a species with a polar functional-group further than a ....
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nonpolar solvent would
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in column chromatography you must switch solvents from nonpolar to polar in order to:
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separate solute by polarity
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Larger column does what, why?
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improve, more polar solutes have more adsorbent to interact with
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Larger diameter does what, why?
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improves, band is smaller fraction of total volume in column
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Smaller sample volume does what, why?
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improves, will be smaller fraction on the column volume
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More concentration does what, why?
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better, band will not diffuse as much
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Shorter load time does what, why?
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better, time to diffuse is limited
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