RP10 - Preparation of a pure organic solid and test of purity Flashcards
What are the stages of synthesising an organic solid?
Preparation
Separation of crude product
Purification
Drying
Check purity
What apparatus is used when separating the solid from the reaction mixture?
Buchner flask
What are the components of a buchner flask?
Buchner funnel
Buchner flask
Rubber tubing
Filter paper
Porous plate
Rubber bung
Filtrate
Describe the recrystallisation method
Dissolve impure crystals in MINIMUM VOLUME OF HOT SOLVENT
Filter solution using gravity filtration using a HOT FUNNEL
Allow solution to COOL AND RECRYSTALLISE
Filter off crystals using suction filtration
Wash by pouring over ice cold solvent
Dry by sucking air out of crystals in buchner flask
Place crystals in low temp oven
Why is a minimum volume of hot solvent used in recrystallisation?
To obtain saturated solution
To increase yield / reduce amount left in solution
Enable crystallisation (on cooling)
Why are the crystals washed with ice cold solvent during recrystallisation?
Remove aqueous impurities
Cold to prevent redissolving and increase amount of crystals formed
Why is the solution filtered hot during recrystalisation?
To remove insoluble impurities
To prevent crystals forming during filtration
Describe how to find the purity of an organic solid
Place solid in melting point tube that is sealed at one end
Place in melting point apparatus and heat slowly
Record temp solid starts to melt and finishes melting
Repeat and average temps
Compare melting points with known values in data book
What are some practical reasons for a % yield of less than 100%
Some product lost during purification
Some product lost when transferring between vessels
How can practical reason for low % yield be minimised?
Rinsing when transferring between vessels
