quiz 1 Flashcards
why did benzoic acid go thru recrystallization?
it was impure so to raise the purity of the benzoic acid
what is recrystallization
-a purification technique
used on organic solids
when would u use recrystallization?
when you have at least abt 100mg of the solid and suspect and know that the solubility properties of the compound to be purified are substantially different
the basic procedure of recrystallization?
- dissolve the organic solid in a solvent that has been heated to boiling
- cool the solution to induce recrystallization
- recrystallized is filtered and dried
What’s important in any recrystallization?
solubility
what is solubility?
max. # of grams of solute that can be dissolved in 100 ml of a given solvent
-often increase with temp. (there is always a max number of g that will dissolve
“like dissolves like”
“solubility increases w temp”
what’s the key decision in recrystallization? what works best as a solvent?
-choosing a good liquid solvent
-a solvent where the organic solid that is being purified is only sightly soluble (or not at all )at room temp but fairly soluble at the boiling point of the solvent
*soluble in hot solvent & insoluble in the same solvent when cold
*solvent that shows poor solubility for the solid when cold, but good solubility when hot
nature of solubility of organic compounds
not very polar=higher solubility in solvents that are also not very polar
why want a solvent that shows poor solublity for the organic when cold, but good solubility when hot?
good solubility to dissolve the crystalline structure in a hot solvent, but poor solubility at low temps to be able to crystalize when it’s cooled.
two types of impurities that can be removed from your organic compound during recrystallization
- insoluble in boiling solvent
-filter by gravity filtration after it has dissolved (trap+ remove insoluble impurities - soluble in cold solvent
-by vacuum filtration
what is distillation?
a separation method when the organic compound to be purified can be
1.safely and easily heated to its boiling point
2. to reduced boiling point at lower pressure (vacuum distillation)
for purification by distillation, what must impurities have
impurities must have different boiling points from the material that you want to purify
when are distillation often used?
it is often used with organic compounds that are
1. liquid at room temp
2. have boiling points less than 200C
the simple distillation process
- heat the liquid mixture to a gentle boil
- vapor expand up the still head & down into the condenser (to cool the vapor back to liquid state)
- the liquid is then flow down into the condenser into the receiver
*distillate: the liquid that collects in the receiver - the temp is measured
if simple distillation fails to separate the impurities, what can be done?
can be improved by using the method of fractional distillation column.
