OCHEM LAB REVIEW Lab 1 Extraction Polarity o Net dipole caused by polar bonds type of bond is characterized by differences in electronegativity If dif is less than 0 2 then nonpolar If dif is between 0 2 and 1 5 then polar yes C H is slightly polar If dif is greater than 1 5 then ionic Hydrogen bonding strong non covalent interactions o Example of intermolecular attractions aka Van der Waals forces o Any molecule with N O F are polar enough to accept hydrogen bonds N H and O H are both donors and acceptors O and F and 3 amines are often Polarity is important to solvation only acceptors no polar hydrogen o Like polarities will associate with each other only Nonpolar alkanes CCl4 Slightly polar ether benzene chloroform Polar alcohols water acetone any N compound o Miscibility ability for two liquids solvents to mix completely If miscible should see only one layer immiscible solvents will form layers based off density Extraction o Separation of 2 compounds based off their differences in solubility and polarity o Solid liquid extraction Adding solvent to a solid and extracting only the soluble compounds think coffee o Liquid liquid extraction 2 compounds both dissolved in a solvent must separate based off polarities Use a separatory funnel swirl and vent to relieve any heat pressure that may build because most of the time acid is added Partition coefficient KD A organic A aq This is important because ratio is a constant therefore doing two extractions is more favorable than one big one because the ratio extracted is proportional to the amount of org solvent added and aq solvent present o Chemically active extraction Manipulating polarity of a compound in order to separate it Good to isolate amines carboxylic acids both are very active specimen To isolate a carboxylic acid or any acid Add a strong base this deprotonates the base o Alkoxide conj Base now more soluble in water so can extract Add strong acid back to alkoxide to protonate separate using organic compound to isolate To isolate an amine basic Protonate with a strong acid making compound more soluble in water Deprotonate amine in aq solution to make soluble in org layer again and extract To extract a nonpolar do both acidic and basic extractions and remaining original compound is purely nonpolar Important New techniques o Steam bath method of heating flammable organic solvents safely Use some boiling stones to prevent bumping Occurs when large bubbles form in solution and burst out which can be messy Boiling stones provide surface area for molecules to vaporize off of safely Never use a full steam bath this creates splashing o Vacuum Filtration Used to separate a solid from a liquid Stabilize the filter flask so it doesn t fall over Apply vacuum only after seal is made terminate vacuum after breaking seal only Terminating vacuum with seal present will cause rush of air to blow sample all over the place o Separatory Funnel for Extraction As explained above swirl and vent several times to avoid build up of heat pressure Always vent away from people and into hood Analyze layers once allowed to settle remember organic compounds are less dense and often settle atop aqueous layer Lab 2 Recrystallization Basic recrystallization schematic o Collision solvent interacts with solid o Dissociation solvent breaks off part of solid bit by bit o Solvation solvent completely dissolves solute o Recrystallization allowing for solute to precipitate Free energy change dictates crystallization and solvation o Solvation is entropically favored increases disorder Therefore solvation can be favored with increase in temperature o Recrystallization is enthalpically favored forming bonds releases heat Therefore favored at low temperatures o Taking a crude solid dissolving it filtering it and then slowly cooling it to precipitate out Recrystallization process a pure compound o Solvent choice Compound of interest should only be soluble at high temperatures called a high temperature coefficient Boiling point of solvent needs to be less than melting point of solid so that when added the solid doesn t melt instead of dissolving called oiling out Should be inert volatile and inexpensive Could mix solvents to create more desirable solvent Impurities must either be completely insoluble or completely soluble in solvent Allows for them to be separated either at filtration step or at recrystallization step o Note adding charcoal will absorb any colored impurities and can easily be filtered away o Filtering step Must keep everything hot to maximize solubility therefore perform hot gravity filtration over steam bath o Recrystallization step Need to spark nucleation Crystal Lattice Theory Spontaneous process where atoms coagulate into crystals Can be facilitated by scratching glass surface area or adding a seed of desired compound surface area Icing solution will further favor recrystallization Forming crystal lattice will only accept like molecules assuming process is slow o Fast nucleation impure crystals due to impurities incorporated Technique review N A accidentally Lab 3 Melting point Boiling point and Distillation Physical properties identity change those that can be observed measured without changing the substances o Intrinsic properties refer to those independent of amount of substance present like melting point solubility polarity density etc o Extrinsic properties refer to those based on external factors like mass volume entropy Physical changes or phase changes occur when compound goes from solid to liquid to gas or any step in between no bonds or broken and no change in chemical composition o Melting point temperature at which transition between solid and liquid is at equilibrium o Is actually a range not a point where melting starts and when solid is completely liquid o Utility Assessing purity small mp range means sample is very pure Comparison to lit value can determine expected range want to match that range ideally Impurities cause freezing point depression interruption of crystal lattice by impurities makes a wider mp range Sample identity comparing exp mp to lit mp to determine identity Mixed Melting Point technique to identify unknown compound that may be one of two different compounds add a small amount of the known compound that it may be o if melting point changes then the unknown is not the same as o if melting point doesn t change then the unknown is the same the known as the known Boiling point temperature at which liquid and gas phases