During the lab, melting points of both the phthalic acid and unknown 1 were taken before and after recrystallization. Before recrystallization, phthalic acid had a melting point of 200-203°C. The range being greater than 2°C difference is indicative of impurities in the sample. After recrystallization, the melting point of phthalic acid was determined to be 207-208°C. The increase in temperature as well as the narrowing range is consistent with purifying the solvent. The presence of impurities in a compound will cause a melting point depression. This depression will be lower than the actual range for the pure compound and at a higher range of values. Both these trends are shown with the data. The melting point of phthalic acid is known to be 207°C (National Center for Biotechnology Information). Due to this information and the trends of melting points before and after recrystallization, the phthalic acid had been successfully purified during the recrystallization. Before being purified, unknown 1 had a melting point of 105-110°C. After recrystallization, the new melting point was 124-125°C. Like the melting point changes seen in phthalic acid, the impure sample of unknown 1 had a wide melting point range, greater than 2°C, which is indicative of an impure compound. The new melting range is also larger, showing the melting point depression which occurring when impurities are found with a compound. Like with phthalic acid, the unknown 1 was successfully purified based on the melting point values.
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