Question

After Carrying out the Aspirin synthesis experiment, Suggest an experiment or technique based on what you have learned in the last few weeks to confirm the preparation of Aspirin. (Give full details) Hint: You are provided with pure sample of Aspirin  

Answer 1

Aspirin: it is synthesized by the reaction between salicylic acid and acetic anhydride, the compound formed named as acetyl salycylic acid.

Melting Point Charecterization:

• the melting point is used to ascertain the temperature at which the kinetic energy and potential energy of the molecules equal.
• purity of aspirin will be determined bassed on the values of the melting range, less pure substances will have a lower melting point and a larger melting range
• The melting range determined using a Thomas-Hoover apparatus.
• First, the samples are packed into the meltingpoint tube. This was accomplished by pressing the open end of the tube into the sample until the sample was about 2mm into the tube.
• the sample was then packed by dropping the tube in a condensor tube, with its closed end down , which minimized the chance of melting point tube breaking.
• the packing technique was important because the melting point analysis requires the smallest size sample that can still be visible during melting.
• large samples or unevenly packed sample will heat unevenly to give erroneous results. three tubes were prepered.
• The Thomas-Hoover apparatus was turned on after the voltage turned to Zero.
• the capillary tube was carefully inserted into the capillary tube openings.
• the stirrer knob was turned so that the mark was about halfway between the slow and fast settings.
• knowing that the melting point range was near 130^oC , the voltage knob was turned to 3.4, which gave a temperature range about 5^oC/minute until 120^oC reached on the thermometer.
• at this the voltage setting was lowered to 3.0.
• the sample was viewed through a magnifying glass . and when the sample first started to melt , the temperature was recorded.
• the final temperature was recorded, when the last sample melted. the melted sample was then discarded.
• this process was repeated three time, and average was taken to determine the melting point range.

caluculation:

the observed melting point range did include the expected melting point. the expected melting point also caluculated from an average was 134^oC . the four sets of melting point data are summerized in the following table.

summery of melting point results

Trial #	initail melting	final melting	notes/observations
1	125	132	1st run ever
2	131	135	-
3	132	135	-
4	131	129.5	Used different apparatus
Average	131.3	133.17	sample 2,3 and 4 used

the results of the first sample ws neglected because that was the first melting point trial performed. the results for the fourth trial were very strange in that the temperature dropped after melting. if only 2 and 3 trails are used then the average range should be 131.5 - 135^oC, which would be very precise results.

consequently , the melting range indicates that the synthesized aspirin pure.