Lab quiz #1 Flashcards
what does the presence of impurities do to melting point
lowers and broadens melting point
melting point depression
bringing a compounds melting point down because it is mixed with a compound with a lower boiling point.
what is the purpose of the vacuum filtration step during melting point lab?
to separate solids from the filtrate at a fast rate
if you have an unknown compound and know it is one of the two known pure compounds you have what should you do?
make two other mixtures: one with unknown and known A and one with unknown and known B. test the melting point. the one that is more precise should let you know what it is
what is recrystallization
technique used to purify solids. includes heating, cooling, and precipitation or crystallization
what is the point of cooling the mixture during recrystallization
separate solids from impurities that are soluble in a cold solvent
what is an ideal solvent during recrystallization
a solvent that will dissolve the compound while hot but will not dissolve the compound while cold
formula for % recovery
(mass recovered material (purified compound)/mass of starting mixture) x 100
why is it impossible to obtain 100% recovery
even at the lowest temp there will always be some solubility
what is distillation
technique to purify liquids by vaporization and condensation
boiling point
the temp at which liquid and vapor are in equilibrium
difference in simple distillation and fractional distillation
simple is single vaporization-condesation cycle while fractional is multiple cycles
is boiling point higher or lower at higher pressures
higher, and lower at lower pressure
do higher altitudes have higher or lower pressure
lower, so compounds will have a lower boiling point
