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Recrystallisation
-Transfer the product from part 1 to a clean 50 mL or 100 mL conical flask, add about 8 mL of ethanol and heat on the hot water bath until all solids have dissolved.
-Into this hot solution pour about 15 mL of water and swirl to mix. Redissolve any precipitate formed at this stage by heating on the hot water bath, and allow it to stand on your bench to cool down to room temperature. Once the solution has cooled down, place the flask into an ice bath to complete the recrystallisation. To get the best results for crystallisation, try not to bump your solution while it is cooling down on the bench.
Q/ Determine the yield of the crude aspirin, show reasoning and full working
In a 50 mL or 100 mL conical flask, mix 3.0 g (0.022 mol) of salicylic acid and 3.0 mL (3.2 g, 0.031 mol) acetic anhydride; add 6 drops of concentrated sulfuric acid using a clean, dry Pasteur pipette (gloves, safety glasses).
-Heat the solution over a boiling water bath (a large beaker of boiling water on a hot plate and the conical flask is suspended in it) for 10 minutes with occasional swirling; all solids should dissolve during this time. Remove the flask from the water bath and add about 10 g of ice to the hot mixture.
-Swirl for a few minutes to hydrolyse the excess acetic anhydride, and then add 10-15 mL of water. Swirl and cool to complete the precipitation of the crude product.
Q/ Determine the yield of the crude aspirin, show reasoning and full working
Write focussed aim/s The aim of this experiment is to prepare; purify and test for purity of the synthesised sample of aspirin
What conclusions can you draw about the nature of the four samples tested for purity? Explain your answers.
Based on the colours produced in your purity test, explain the test and what is your conclusion about the relative purity of recrystallized aspirin sample supplied and commercially available aspirin?
(iii) The enthalpy change (ΔH) for this reaction is –3509 kJ when one mole of pentane burns in oxygen.
The reaction is carried out at a pressure (p) of 100 kPa.
The change in volume (ΔV) is 0.21m3.
Calculate the change in internal energy (ΔU) for this reaction.
ΔH = ΔU + pΔV
Show your working.
(3)
Write the sequences of peptides that would be released from the following peptide by the
treatment of trypsin?
Heptadecapeptide Cortistatin DRMPCRNFFWKTFSSCK
in what order would the following globular proteins emerge/eluted on gel filtration of a mixture on Sephadex G200? Ribonuclease (Mr=12,000), aldolase (Mr=159,000), hemoglobin (Mr=64,000), β-lactoglobulin (Mr=36,000), serum albumin (Mr=65,000).
