Recrystallization

Most important method for the purification of ingrained solids Separation of changes based on differences in solubility between the compound of interest and its contaminants Basic technique 1 . Dissolve adulterate visitation in an appropriate het resolve Part A Choosing a resolve Part B Purification of phonic 2. Cool root word slowly to induce crystal growth 3. Filter ensueing mixture to sequestrate crystals Reading Mooring, Hammond & Chats Chi. 15 pigs 183-197 Chi. 0 pigs 104-113 Chi. 14 pigs 174-182 Scale 5-10 MGM coverer based inquiry a new material prepared in a laboratory 1,000 keg + commercial applications sugar refining, synthesis of pharmaceutical agents, etc. molecular(a) selection pure magnetic core aggregation begins based on surface, shape, & functionality molecules cohere on growing surface in orderly manner, excluding those of different size of shape if deposition occurs too quickly, an impure substance gutter result crystal defects incorporated impurities Rationalization Steps 1 .Choose an appropriate solvent compound (solid) should be soluble when solvent is hot compound should be pissing-insoluble when solvent is cold may require some ladder & error 2. Dissolve impure compound in the minimum measuring celestial pole of hot solvent too much solvent & compound may not come out when cool 3. Decolonize solution if needful with activated charcoal (Norris) skip this step if no/ few sloped impurities are present be sure your compound is not hypothetical 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 scum bathing tub if no crystals form scratch flask with glass rod or ad a seed crystal to the solution first of all cool to room these methods provide a nucleation appoint for crystallization 6. hive away and wash the crystals collection typica lly by filtration (large quantities) for small quantities can take out solvent with a pipette wash crystals with a small add up of ice cold solvent filtrate (mother liquor) can be concentrated to get 2nd crop 7.Dry the crystals thoroughly implement vacuum & continue suction until crystals are dry dry crystals nevertheless under vacuum in a side arm test tube can also press solids between two pieces of filter out paper Factors that Influence Melting Point Melting Point point 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 melt down point temperatures 1.Intermolecular forces start temperature at which first drop of liquid forms a. Van deer Walls interactions actually reeking end temperature at which all solid has turned to liquid b. Dipole-dipole interactions e. G. 82-ICC wherefore do we care about melt point? 1. Can be used to help identify substances ampere pm of unknown substance with that of known substance result from popularization of bonds c. Hydrogen bonding compounds having O-H or N-H bonds d. Ionic forces take a mixed break up point 2. Is an index of purity pure haves 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 surface molecules need the same elan vital to escape. Leads to a narrow melting point range. For melting to occur, surface molecules moldiness have enough null to break free. Stronger intermolecular interactions = more energy required for molecules to escape.Translates to a higher pm. In an impure sample, intermolecular forces are recessed in the region of the impurity. Less energy olibanum required for surface molecules to break free. Crystal begins to liquefy at a lowe r temperature structural features that influence how molecules pack together impact melting point temperature symmetrical compounds typically have higher melting points features that disrupt crystal lattice lower melting point Next calendar week Experiment 2 Rationalization & Melting Point A.Choosing a Solvent identify an appropriate solvent for the rationalization 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 Thin Layer Chromatography science laboratory Report (expo 1) Lab Reports are due at the beginning of your regular lab academic term Still some regions without impurities. Additional energy required for surface molecules in these regions to break free. End result is that melting point range is broadenedExperimental expand 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 absolute mass to the 1st tube, add 0. 5-1 ml of one 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