rp10 Flashcards
recrystallisation (4)
- dissolve in minimum volume
- of hot solvent
- hot filter
- allow solution to cool and crystals to form by putting crystals in ice
- pressure filtration
- wash with distilled water
- dry crystals
why is solvent choice important?
so the desired compound in pure crystals is formed
why is the minimum volume of hot water used?
to obtain a saturated solution that crystallises on cooling
why is hot solution filtered?
removes insoluble impurities before crystals can reform
why is ice used to cool?
slow cooling ensures all compound crystallises, ice increases the yield
why are buchner funnels used?
faster filtration due to reduced pressure
why are crystals washed with cold water?
to remove soluble impurities
why are crystals dried?
to remove excess water as water would affect % yield
why ethanoyl chloride isn’t usually used
hcl gas released, toxic
point where impure compounds melt
below expected value and over a large range
increasing yield from distillation
heat to exact boiling point, cool the collecting vessel
purpose of a separating funnel
separate liquids based on densities
steps in purifying an organic liquid
- distillate of impure products into a separating funnel
- wash product with sodium hydrogencarbonate and shake, release co2
- allow layers to separate, discard the aqueous layer
- run organic liquid into a conical flash and add drying agent
- distil liquid to form pure product
how do you know when a drying agent has worked?
liquid turns from cloudy to clear
use of fluted filter paper
to prevent precipitation of the solid
