Lab 2 - Crystallization Sketch of apparatus: Fig. 4.1, 4.3,...

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Crystallization Sketch of apparatus: Fig. 4.1, 4.3, 4.15 o label Crystallization : a method to purify solids 4 important concepts to consider in the process of recrystallization: o solubility o saturation level o exclusion o nucleation o **read details on how these concepts are employed and what is involved on p 61 Impurities: o may come from reactions: side products, unreacted starting, materials, inorganic materials, solvents o may come from storage: decomposition, contamination from other chemicals o may be trapped within the crystal lattice or on the surface of the solid Seven Steps of crystallization *need to know all 7 o remember : like dissolves like – polar solvents dissolve polar solutes, nonpolar solvents dissolve nonpolar solutes ask yourself: is it polar or non polar? o Polarity and solubility of organic compounds are affected by : molecular weight if comparing compounds with the same functional group (lower = more soluble) proportion of hydrocarbon in molecule in functional group w/in the molecule (higher proportion = lower polarity) o Step 1 : choosing solvent and solvent pairs ideal characteristics for solvent w/ respect to solute dissolves the solute completely when solvent is hot (at BP of solvent) precipitates solute completely when solvent is cold does not react with solute back to like dissolves like—if solute and solvent are too similar in polarities, solute will dissolve even in cold solvent if solute and solvent have very different polarities, solute will not dissolve at all So—must be a balance in polarity Ideal characteristics for solvent w/ respect to impurities : does not dissolve impurities at all o so impurities can be filtered off from hot solution OR dissolves impurities very well (even when solvent is cold)
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o so impurities along with cold solvent can be removed from crystals via filtration other characteristics : read p. 62 **questions will be asked read about desirable and undesirable qualitites of water, ethanol, ethyl acetate and acetone (common crystallization solvents) Solvent pairs – characteristics both solvents have to be miscible in each other— homogenous mixture
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Lab 2 - Crystallization Sketch of apparatus: Fig. 4.1, 4.3,...

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