CHEM 253 Report 3 PDF

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Experiment 3: Recrystallization and Melting Point Lab Section: 012 Lab 3: Recrystallization and Melting Point 11 Feb 2021 Purpose The purpose of this experiment is to purify naphthalene via recrystallization and determine its percent recovery as well as the melting points of the recrystallized naphthalene, cinnamic acid, urea, and a mixture of cinnamic acid and urea. Theory Recrystallization is a method for purifying a substance wherein a substance is dissolved in hot solvent then cooled to form crystals of the pure substance. Some of the substance will remain dissolved in solution, so it is important to use only the minimum amount of solvent. The melting point of a substance can be used to determine the purity and identity of substances by comparing the melting point range of an unknown substance to the melting point ranges of known substances. The closer the melting point of a substance is to its theoretical melting point, the more pure the substance is. Reaction

Methanol to use: naphthalene∗100 mLmethanol 0.5 g =5 mLmethanol 10 g naphthalene (Calculated using solubility of naphthalene in methanol at 100C = 10g/100mL) Amounts used: - Naphthalene: 0.50 g - Methanol: 5 mL Percent recovery (naphthalene): - Initial: 0.50 g - Final: 0.35 g 0.35 g ∗100 %=70 % recovery - Percent recovery = 0.5 g Methods/Procedures 1

The experiment procedures were followed verbatim from the lab manual as found on page 20, with no exceptions. Naphthalene, cinnamic acid, and urea are all irritants to the skin, eyes, and lungs, so goggles and gloves were required to be worn in this experiment, and experimenters avoided breathing in the chemical fumes. Naphthalene is flammable, so it must be kept away from heat, and the naphthalene crystals had to be dried at room temperature instead of the oven in order to avoid combustion. Observations/Results When adding the methanol, bubbling occurred, getting more aggressive as more was added. The solution smelled like mothballs. When measuring the melting points, the crystals started to look shiny at the beginning of the melting point range, and then were fully liquid at the end of the range. It is possible the crystals could have been drier, but it was important to avoid using the oven since naphthalene is flammable. The naphthalene yielded from recrystallization was 0.35 grams; less than the initial 0.50 grams, yielding a percent recovery of 70%. The melting point ranges for the substances were as follows: - Naphthalene: 73 – 76 C - Cinnamic acid: 110 – 128 C - Urea: 129 – 133 C - Cinnamic acid/ urea mixture: 95 – 125 C Discussion/Conclusion The experiment went mostly as planned, though a higher percent recovery would have been desirable. Purification and recrystallization was successful. The melting point ranges found were close to the theoretical values (naphthalene 80.3C, cinnamic acid 133C, urea 134C). The melting point for naphthalene was lower than expected, meaning the product had impurities. The melting point of the cinnamic acid/ urea mixture was lower than the melting points for those individual compounds, due to being impure. Exercises 3) 0.278 mL water; 1.722 mg phthalic acid g∗100 mL =0.277778 mL water 0.05 18 g mL∗0.62 g 0.278 =0.00172 g ;=1.722 mg phthalic acid 100 mL 7) A mixed solvent may be used in recrystallization if the substance to be recrystallized isn’t fully soluble in any one solvent. Further, impure substances may require different solvents to recrystallize each compound within. Raw Data See below

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