Lab final Flashcards
What are the step for recrystallization
Find good solvent Heating Precipitation Filtration Drying
What does it mean to find a good solvent in recrystallization
find a solvent with a high bp but not too high that evaporation takes too long (50-80 C)
What does heating mean in recrystallization
add solvent to organic acid and heat until solid is fuly dissolved
What does precipitation mean in recrystallization
slower the process, the better the yield. Use an ice bath to cool further
What does filtration mean in recrystallization
vacuum to get rid of liquid, rinse so that soluble impurities are removed
What does drying mean in recrystallization
air is pulled over crystal and they are then put in oven
What properties affect separation in GC
Polarity and boiling point. Higher polarity causes substance to interact with columns more and higher bp have higher retention time
what substrate/solvent will be in each layer of extration and why
Acids/bases will partition into an aqueous layer if charged but if there is no separation then an acid/base needs to be added so that there is a loss/gain of electron causing them to partition (aqueous layer is on top)
Why do we dry reagents in extraction
to remove organic solvents and water from substances to leave them pure
What is the melting point
temp at which substance is at equilibrium at standard pressure (more of a range)
How do impurities affect melting point
Lower melting point and broadens range
How do you calculate Rf values
Distance spot traveled divided by distance solvent traveled
How do you separate and isolate two enantiomeres
Decant methanol, transfer crystals to a separatory funnel, extract with DCM, and separate and dry organic layer
What does it mean to decant methanol when separating enantiomers
Liquid is poured from one container to another, leaving sediment at the bottom of the first layer. Doing so with methanol, separates amine tartrate crystals that will be used.
What does it mean to transfer crystals to a sepratory funnel when separating enantiomers
Set up sepratory funnel, put crystals in, add water to dissolve some of the crystals, add NaOH then swirl to further dissolve crystals
What does it mean to extract with DCM when separating enantiomers
Add DCM to funnel and shake while venting to ensure all solids are dissolved. This will create two layers with the lower one having the free amine
What does it mean to separate and dry organic layer when separating enantiomers
Lower layer is drained along with amines in it. DCM is added to the separatory funnel and then shaken and allowed to separate. The lower layer is then added to previous extraction. K2CO3 is added to extraction to dry it and then filtered to further dry and then put into the roto vap
How does polarimetry work
Measures the direction (CW or CCW) and extent to which a sample interacts with polarized light. The difference in enantiomers will interact with polarized light in different fashions
What is the equation for IHD
C x 2 + 2 + N - H - X all dividied by 2
