Physical Property DATA Measurements Part ABLE and 1 on of Partner\'s Name Mass o
ID: 489215 • Letter: P
Question
Physical Property DATA Measurements Part ABLE and 1 on of Partner's Name Mass of Benzoie sample Acid points) (g) Recrystallization l S. 365 Calculated volume of water needed lds a of filter paper Mass of filter paper career 46 Mass and product .an of recrystallized (g) product (g) Part II Percent Benzoic Acid Recovered Recrystallization of Aspirin (o points) Mass of sample (g) aspirin Mass Mass of filter paper (g) Mass of filter paper or and product (g) 6. 17 ta Mass of recrystallized product (g) Percent Aspirin Recovered Part III Melting Temperature (5 points) Experimental melting Accepted melting point point range (OC) range Benzoic acid Aspirin 36 Reference TST,5°C 57Explanation / Answer
Melting Point of a solid can be defined as the temperature at which solid and liquid are in equilibrium at 1-atmospheric pressure. Pure organic compounds always have a sharp melting point.
Eg: Benzoic acid melts at 122 oC and the Acetylsalicylic acid (Aspirin) melts at 139 oC.
If the melting point value of the sample after recovery and recrystallization is found to be within a degree of the accepted value then, the sample given is a fairly pure sample.
Usually, the difference in the melting point for the pure sample as in your case is either by the personal error or the apparatus error. The heating rate of the sample in the capillary is very important, there should be a steady increase in the rate of heating ie., Maximum of 1 to 2 degrees per minute rise will always give you good results. Fail to follow this, results in poor results. Although there has to be a single temperature at which a pure solid and liquid are in equilibrium there happens to be a range always this because the temperature inside the bath will raise little during the time it takes the sample to melt.
It is advised that run the first sample at the high rate of heating as we do in case of titration (first titration value will be used as the reference for the next titrations). In the same way, repeat the procedure at a faster rate for the same sample but this time slow it down when you are approaching the expected melting point.
Minimum of 3 to 4 mm in the bottom of the capillary tube must be filled firmly for effective heat transfer.
Your sample must be completely dried so that there should not be any moisture in the sample which results in variance in the melting point. The solvent used for the recrystallization must be pure and glasswares used should also be clean. Human error in observing the readings on the scale.
The presence of impurities in the sample will result in melting over a wide range of temperature resulting in an impure sample and sharp melting point less than the actual melting point is often evidence for a fairly pure sample.
You have been given a pure sample and asked to recrystallized and check for melting point, by looking at your results it is evident that your sample is fairly pure.