exp 2 post lab Flashcards
SALICYLIC ACID
- occurs as a ___ compounds in ____
- physical properties?
- solubility
- chemical formula
- functional groups (2)
- molar mass
- exhibits ____ bonding
- natural compound in plants
- odorless white to light tan solid
- soluble in water at 25 C: 2.24 g/mL
- HOC6H4COOH
- carboxylic acid and hydroxyl/phenol
- 138.12
- hydrogen bonding
Melting point of pure salicylic acid
158 - 159 C
4 components of SALICYLIC ACID mixture
- Desired compound (pure SA)
- Totally insoluble impurities
- Totally soluble impurities
- Hot recrystallizing solvent
How are INSOLUBLE IMPURITIES separated from the mixture?
hot gravity filtration
How are SOLUBLE IMPURITIES separated from the mixture?
after hot gravity filtration, cool the hot mixture to room temp
the desired pure compound of SA will start to crystallize
through SUCTION FILTRATION, soluble impurities + majority of the solvent will be removed
How to remove excess recrystallizing solvent and traces of soluble impurities from the pure desired compound?
Wash with cold solvent + suction filtration
The 3 recrystallizing solvent choices for the experiment:
+ which is the appropriate?
- water (appropriate)
- 95% ethanol
- acetone
Effect of using too much recrystallization solvent on crude sample
in terms of recovery and purity
- leads to unsaturation/dilution (which may make recrystallization difficult to occur)
- lowers recovery but no effect on purity
How much recrystallization solvent to dissolve sample? + why (1)
minimum amount
- ensure maximum yield of crystal
Criteria for choosing the APPROPRIATE SOLVENT for RECRYSTALLIZATION (6)
- Desired substance must be soluble in the solvent at ELEVATED temperature
- Solvent should not react with desired substance
- Impurities should totally soluble or insoluble (not partially)
- Boiling Point of solvent should be less than the melting point of the desired substance
- Solvent must be relatively volatile
- Solvent must be safe, non-toxic, and inexpensive
After washing with cold solvent, how to remove traces of the cold recrystallizing solvent?
air dry
Effect of using too less recrystallization solvent on crude sample
- lead to premature recrystallization
- higher recover but lower purity
why should hot gravity filtration be HOT?
- prevents premature recrystallization
- avoids impurities
FLUTED FILTER PAPER
importance (2)
- maximizes the surface area for filtration
- minimizes contact with walls of the funnel
STEMLESS FUNNEL
importance (2)
- avoid clogging
- prevent rapid cooling of solution
DECOLORIZING CARBON / ACTIVATED CARBON
- what type of molecules does it attract?
- pure sample is colored, should this be used?
- pure sample is colorless, should this be used?
- pure sample is polar, should this be used?
- pure sample is nonpolar, should this be used?
- nonpolar molecules kasi pure CARBON siya
- no, kasi baka matanggal din color ng sample (or small amounts)
- yes, most effective
- yes, most effective
- no, didikit yung pure sample sa carbon at maiiwan sa hot gravity filtration
What is added to fluted filter paper in hot gravity filtration and why?
CELITE
- used as a filtration medium
- prevent penetration of decolorizing carbon while maintaining enhanced carbon
RECRYSTALLIZATION is based on the principle that the ___ of most solids ___ with ___ temperature
- solubility
- increases
- increased
RECRYSTALLIZATION
- involves _____ ___ of filtrate placed in an _____ bath
+ why need gawin?
- slow cooling
- ice
slow cooling muna kasi pag linagay sa ice bath agad, pwede mabasag glass ware or mag crystallize agad which can lead to impurities
which will crystallize more assuming there were more of the former than the latter:
crude desired substance
impurities
crude desire substance
the slower the rate of cooling, the ____ the crystals formed
larger
in cases, why does recrystallization not occur rapidly?
how to initiate recrystallization?
- due to a kinetic barrier to crystal formation
- Scratching inner walls of beaker or glass container (release tiny fragments of glass and provide energy from vibrations)
- Addition of seed crystal (small crude or pure solid)
INITIATION of RECRYSTALLIZATON
WHAT does the 2 ways provide?
- it is the initial process that forms a site upon which additional particles are deposited as the crystal grows
- where mixture particles can palibot to initate their recrystallization
NUCLEATION SITE
What happens if suction filtration is used instead of hot gravity filtration?
rapid cooling due to cold air from vacuum -> premature recrystallization
when is suction filtration used?
after cooling of sample (pagtapos ng hot gravity filtration) and may crystals na na form
suction filtration is used to remove the majority of recrystallization solvent + soluble impurities
then wash with cold solvent afterward to remove traces of soluble impurities
what happens if crystals are not washed with cold solvent?
what if hot solvent is used?
*in terms of recovery and purity
- increase recovery, lowers purity
- decrease recovery, no effect on purity
MELTING POINT
- temperature in which the ____ and ____ states of a substance are in ____ or are _____- _____
- purpose?
- what bath is used to determine this?
- what is the initial step done?
- solid and liquid
- equilibrium
- co-existing
- to establish a pure substance’s identity
- oil-bath method
- pulverize on watch glass
why cant the pure crystals (product) be pulverized in the filter paper directly?
kasi may “lints” ang filter paper na pwedeng dumikit sa crystals and decrease impurity
MELTING POINT RANGE??
- temperature in which solid starts to melt
- temperature in which the last trace of solid turns to liquid
and the average of the 2
3 CAUSES of ERRORS in melting point determination + why
- Rapid heating - higher melting point than literature value
- Presence of Impurities - lower melting point than literature value
- Loose, uneven packing of crystals - widens melting point since more solids will be melted
