Experiment 1 & 2 Discussion PDF

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Experiment 1 & 2 Discussion...

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Using the solubility of phthalic acid in water that was given (18g/mL in boiling water and 0.54g/mL in chilled water) it was calculated that 5.56mL of boiling water would be required to dissolve 1g of phthalic acid. Though experimentally it was determined that 1.004g of phthalic acid required 7.8mL of boiling water to dissolve. The higher volume of water required could have been caused because some of the water evaporated while it was boiling and because the impurities present were less soluble compared to phthalic acid in the water. The percent recovery of the phthalic acid after recrystallisation was 87.649%. This could suggest that the phthalic acid was not very pure and the impurities were removed during the process of recrystallisation. Phthalic acid is also still slightly soluble in chilled water, as mentioned above, with 7.8mL of chilled water being able to dissolve 0.0422g of phthalic acid (4.22% of 1g of phthalic acid). The collected mass after recrystallised could also have been inaccurate as the phthalic acid dried to be flaky and delicate, it stuck easily to different surfaces causing there to be loss of mass while being transferred onto the weighing paper. The phthalic acid could also have not completely recrystallised before it was vacuum filtrated further leading to loss of mass. Suitable solvents for recrystallisation are solvents that dissolve the compound when heated but recrystallise the compound after the solvent has been chilled. It was experimentally concluded that acetic acid, toluene and ligroin were suitable solvents for benzoic acid recrystallisation. While water and acetic acid were determined to be suitable solvents for resorcinol recrystallisation. These compounds dissolved in the solvent when it was heated but not when the solvent was room temperature, and crystals formed after the solution was cooled suggesting that they are suitable solvents for recrystallisation of these compounds.

Using spartan it was determined that both Benzoic Acid (3.40debye) and Resorcinol (3.15debye) are polar molecules. It was also determined that all the solvents except toluene and ligroin were polar molecules. Though experimentally resorcinol was soluble in toluene suggesting, and benzoic acid was determined to be soluble in both ligroin and toluene was the solvents were heated. This suggests that even though the solvent and compound are not both polar or nonpolar the compound can still be soluble in the solvent. This could be because the solubility of a substance in a solvent is determined by the intermolecular forces between them and the entropy change associated with the solvation Hence, determining if a compound is soluble in a solvent can not be purely concluded by looking at the polarity (dipole moment) of the compound and compared to the polarity of the solvent. The unknown compound (114S) was determined to be trans-stilbene because the unknown compound mixed with benzoic acid and succinimide caused the melting range to decrease significantly, but the mixture of the unknown and trans-stilbene was the same as the melting range of the pure trans-stilbene. Mixtures caused the melting point to decrease because the different compounds would have disrupted each other's crystal lattice structures, hence, lowering the melting point. The percent recovery of cholesterol was only 38.462%. The low percent recovery, makes sense as not the entirety of a gallstone is made of cholesterol and only parts of it are. Though the cholesterol was slightly wet when it was transferred onto the watch glass to dry hence some of the crystals became attached to the watch glass after it dried. While transferring the cholesterol to the weighing paper mass was lost. The melting range of the cholesterol was experimentally determined to be 143.2 - 146.4°C. This suggests that the recovered cholesterol decently pure as the theoretical melting point of cholesterol is 148°C and the melting range was only slightly lower than the theoretical value....