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CH 337 Midterm
| Question | Answer |
|---|---|
| In chronological order what steps constitute a typical solid-liquid extraction? | 1. Addition of the solid mixture to a suitable flask 2. Addition of the extraction solvent 3. Outfitting the flask for heating under reflux 4. Refluxing the suspension 5. Cooling the suspension 6. Isolation of the filtrate by gravity filtration 7. Removal of the solvent by evaporation |
| What are the four principle categories of weak intermolecular interactions ranked strongest to weakest? | 1. Hydrogen binding 2. Dipole-dipole interactions 3. Dipole-induced dipole interactions 4. Induced dipole-induced dipole interactions |
| In the context of melting point determination how much sample should be added to the glass capillary tube? | 2mm |
| Recrystallization is the major mode of purification for compounds in that phase? | Solid |
| In the context of recrystallization what consequences are associated with slow crystal growth? | Larger, purer crystals |
| In the context of recrystallization what consequences are associated with fast crystal growth? | Smaller, less pure crystals |
| In order to obtain a purer sample through recrystallization what must be true about impurities? | In the best case scenario, the impurities dissolve in the hot solvent and remain in the solution even as the hot saturated solution is cooled. Alternatively, the impurities do not dissolve in the hot solvent, this would require a hot gravity filtration step after which the hot saturated solution would be allowed to cool. |
| What are the three most important attributes of an ideal recrystallization solvent? | 1. Be chemically inert 2. Have a very high capacity (per unit volume) for the solute of interest at the boiling point of the solute AND have a very low capacity for the solute of interest at a temperature just above the solvent's freezing point 3. Dissolve impurities at all temperatures OR not dissolve impurities at any temperature |
| Upon what does the separation of two or more liquid compounds by distillation depend? | Boiling point differences |
| Upon what does the boiling point of a mixture depend? | The vapor pressures of the various components |
| For how long should one dry a product that has been recrystallized from a high boiling-point solvent? | At least overnight |
| What rate of distillate collection indicates a slow, steady distillation? | 1 drop of distillate ever 2-3 seconds |
| During distillation how does the composition of the liquid remaining in the distilling flask change? | The liquid remaining in the distilling flask becomes richer in the less volatile component |
| During distillation how does the boiling point of the liquid remaining in the distilling flask change? | It raises |
| In the context of distillation how should the distilling flask/three-way adapter assembly be positioned? | Vertically |
| In the context of distillation upon what does the efficiency of a fractionating column depend? | The number of vaporization-condensation cycles (theoretical plates) |
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