Practical 10a: Making Aspirin Flashcards
Process of recrystallisation
Dissolve crude products in minimum hot solvent
Filter mixture to remove insoluble impurities
Cool solution to room temperature then add to ice bath to start precipitation
Seperate mixture using reduced pressure
Wash and dry to get final products
You are provided with a sample of pure aspirin in a melting point tube. Describe briefly how you would determine the accurate value for the melting point of aspirin
Heat melting point tube in an oil bath
Slowly near the melting point
Why is the sample dissolved in a minimum sample
To produce a saturated solution
Why is the sample dissolved in hot water
Increases yield
Why is sample filtered hot
Remove insoluble impurities
Why is the sample cooled in ice
To maximise crystallisation
Why is the sample washed with cold water
To remove any soluble impurities
Why was the flask cooled to room temperature before the crystals were filtered off
There would be a lower yield if it was warm
Why were the crystals compressed in the funnel
Air passes through the sample not just around it
The melting point of the sample obtained was found to be slightly lower than the data book value
Suggest the most likely impurity to have caused this low value and an improvement to the method so that a more accurate value for the melting point can be obtained
Water
Press sample between filter paper
Give a safety precaution & reason
Precaution: wear gloves
Reason: acid is corrisive
Draw equipment for filtering + label
Label required:
Buchner funnel
Filter paper
Vaccum pump
Bung
