Recrystallization

nearly important method for the purification of organic solids Separation of compounds based on differences in solubility amongst the compound of interest and its contaminants Basic technique 1 . Dissolve impure(a) sample in an set aside acid solvent Part A Choosing a Solvent Part B Purification of phonetic 2. Cool dissolvent slowly to induce watch glass growth 3. filtrate resulting mixture to isolate crystals interpretation Mooring, Hammond & Chats Chi. 15 pigs 183-197 Chi. 0 pigs 104-113 Chi. 14 pigs 174-182 Scale 5-10 MGM coverer based research a new material lively in a research science laboratory 1,000 keg + commercial applications sugar refining, synthesis of ph artilleryaceutical agents, etc. molecular(a) selection pure substance aggregation begins based on size, shape, & functionality molecules deposit on growing muster up in orderly manner, excluding those of different size of shape if deposition occurs too quickly, an impure substance arouse result crysta l defects incorporated impurities Rationalization Steps 1 .Choose an appropriate solvent compound (solid) should be soluble when solvent is alive compound should be insoluble when solvent is cold may adopt some trial & error 2. Dissolve impure compound in the minimum amount of hot solvent too much solvent & compound may not come out when cool down 3. Decolonize solution if needed with activated charcoal (Norris) skip this step if no/ few diagonal impurities argon present be sure your compound is not supposed to be colored 4. Filter off any insoluble materials insoluble impurities and/or activated charcoal done while solution is hot 5.Slowly cool the resulting solution to induce crystallization temperature, then in an ice bath if no crystals form scratch flask with glass rod or ad a seed crystal to the solution first cool to room these methods provide a nucleation lay for crystallization 6. Collect and mop the crystals collection typically by filtration (large quanti ties) for small quantities bay window remove solvent with a pipette airstream crystals with a small amount of ice cold solvent filtrate (mother liquor) can be concentrated to get 2nd crop 7.Dry the crystals thoroughly apply vacuum & continue suck until crystals are dry dry crystals gain ground under vacuum in a side arm test tube can also press solids between two pieces of filter paper Factors that model Melting Point Melting Point mind of equilibrium between crystalline & liquid states point at which a crystal goes from solid to liquid Temperature at which a compound melts is typically a range Factors that influence run point temperatures 1.Intermolecular forces start temperature at which first drop of liquid forms a. new wave deer Walls interactions very weak end temperature at which all solid has turned to liquid b. Dipole-dipole interactions e. G. 82-ICC why do we care about melting point? 1. Can be used to help recognise substances ampere pm of unknown substan ce with that of known substance result from popularization of bonds c. Hydrogen bind compounds having O-H or N-H bonds d. Ionic forces take a mixed melting point 2. Is an indicator of purity pure samples have narrow pm ranges (0. 2 co) impure samples melt over a broader range (ICC) & are depressed very strong 2. Shape strength & nature of intermolecular interactions impact melting point temperature Melting Point as an Indicator of Purity In a pure sample, all jump molecules need the same zilch to escape. Leads to a narrow melting point range. For melting to occur, surface molecules must have enough energy to break free. Stronger intermolecular interactions = more energy required for molecules to escape.Translates to a higher(prenominal) pm. In an impure sample, intermolecular forces are disrupted in the region of the impurity. Less energy thus required for surface molecules to break free. Crystal begins to liquefy at a lower temperature structural features that influence ho w molecules pack together impact melting point temperature symmetrical compounds typically have higher melting points features that disrupt crystal lattice lower melting point Next Week experiment 2 Rationalization & Melting Point A.Choosing a Solvent identify an appropriate solvent for the rationalisation of phonetic B. Purification of Phonetic purify the impure solid evaluate success by melting point & TTL Come prepared. You will get only one sample of phonetic DUE swerve Layer Chromatography Lab Report (expo 1) Lab Reports are due at the beginning of your regular lab session Still some regions without impurities. Additional energy required for surface molecules in these regions to break free. residual result is that melting point range is broadenedExperimental Details Part A prepare a hot water bath begin heating as soon as you arrive in lab put a spatula tip of the impure compound into a small test tube no need to get an accurate mass to the 1st tube, add 0. 5-1 ml of on e of the solvents to be tested 10-20 drops (1 drop = ca. 0. Ml) evaluate behavior upon addition of solvent, when hot, when cold if compound dissolves upon addition, no need to go further if solids remain, heat in hot water bath to near boiling