Organic Chemistry Lab Report #1 PDF

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Melina Rosado

Chemistry 2612 Organic Chemistry Lab

Lab Report #1

Melting Point of Benzoic Acid and Salicylic Acid; Recrystallization of Dirty Benzoic Acid and Unknowns

02-06-17

Introduction Melting points is a method used to determine the temperature of a molecule in which can change its physical properties from a solid state to a liquid state. For melting point to happen there needs to be enough thermal energy to break the crystal lattice of the substance being tested. One of the purposes of this method is to determine how pure is the substance. There are two factors that determine melting point; Intermolecular forces and symmetry. The more symmetry the molecule has, the higher the melting point, and the stronger the intermolecular forces the higher the melting point. If the boiling point of the substance is less than expected, there is always the possibility that there are impurities in the substance. Recrystallization is a purification method in which the crystals are separated from its impurities. The higher and stronger the intermolecular forces of the pure substance, prevents an impurity from forming. The compound is dissolved in solvent and its heat up, the insoluble impurities are filtered and then cooled for down for precipitation to occur and then compound is set separately for suction filtration. Melting point is taken to determine the purity of the substance.

Chemical Properties and Safety Compound

Benzoic Acid (C7H6O2)

Molecular Weight (g/mol) 121.2

Melting Point (°C)

Hazards

121-122

-Irritant of skin, eye, ingestion & inhalation -Toxic to lungs, nervous system, and mucous membranes

Salicylic Acid (C7H6O3)

138.12

156 - 158

-Irritant of skin, eye, ingestion & inhalation -Capable of breaking down fats and lipids, causing burn of the skin in high concentrations

Acetanilide (C8H9NO)

135.16

113 – 114

-Irritant of skin, eye, ingestion & inhalation

Cinnamic Acid (C9H8O2)

148.15

132 – 133

-Irritant of skin, eye, ingestion & inhalation

78.37 **Boiling Point (°C)

-Irritant of skin, eye, ingestion & inhalation

Ethanol (C2H6O)

-Carcinogenic, mutagenic, & teratogenic effects in high concentrations -Toxic to blood, the reproductive system, liver, upper respiratory tract, skin, & CNS

Experimental Procedure of Melting Points Part A. Melting Point of Pure Compounds A sample of benzoic and salicylic acid were taken on separate watch glasses. Two capillaries with each compound were prepared. The thermometer was placed in the Melting Temperature apparatus and the voltage was turned on to 5 until the thermometer would give a temperature between 90-95°C. The two samples were placed in the Melting Temperature apparatus side by side. The temperature range of both compounds were recorded when these went from a solid to a liquid. Part B. Melting Point of 50:50 Mixture A sample of the 50:50 mixture was taken in a separate watch glass. A capillary was prepared to be put in the Melting Temperature Apparatus. For this second part, the voltage was taken down to 2 so the temperature would be lowered to 90-95°C to take the melting point again. The capillary was placed in the apparatus and the temperature of the mixture was recorded when it went from a solid to a liquid. Experimental Procedure for Recrystallization Part A. Recrystallization of “Dirty” Benzoic Acid A sample of 1.012 grams of “dirty” benzoic acid was dissolved in water (25 ml) on a Erlenmeyer flask over a hot plate (200°C) and waited about 10-15 min until the mixture boiled. Another flask was prepared with a short-stemmed funnel and fluted filter paper and placed in the hot plate. Once the “dirty” benzoic acid was dissolved, it was filtered in the hot flask. The flask was left to cool down for 10 min for precipitation to occur. After the 10 min, the Erlenmeyer

flask was placed into an ice bath for another 10 min so precipitation can be completed. After the ice bath, the Buchner Funnel was used to finish filtration of the crystals. The crystals were placed in a watch glass and then under the heat lamp until dry. Once dry a sample with a capillary was prepared to test melting point. For the last step, the weight and temperature range of the crystals was taken and recorded. Part B. Recrystallization of Unknown A sample of 2.011 grams of unknown “D” was taken and put into a 125 Erlenmeyer flask over a hot plate (200°C) and dissolved in 95% ethanol (6 ml). A 100ml beaker was prepared with a short-stemmed funnel and fluted filter paper and placed in the hot plate. Once the mixture boiled it was filtered in the beaker. The filtrate was kept hot and added no more than 15ml of water until the solution turned turbid. The mouth of the beaker was covered and let cooled down for 10-15 min. Once 15 min passed the beaker was placed in an ice bath for crystallization to be completed. A Buchner funnel was used for filtration of the crystals. The crystals were placed in a watch glass and put under the heat lamp until dry. Once dry, the weight and the temperature of the crystals were taken. Percent recovery and identification of the compound was recorded.

Data and Observations Compound Benzoic Acid (C7H6O2)

Melting Point (°C) 120-127

Salicylic Acid (C7H6O3)

155-160

50:50 mixture of Benzoic Acid & Salicylic Acid

105-110

Compound

Dirty Benzoic Acid (C7H6O2) Unknown Compound

Initial Mass (grams) 1.012 2.011

Mass of Product (grams) 0.365 1.046g

Melting Point (°C)

118-120 153.3-159

Calculations

Percent recovery=

material recovered x 100 starting material

Percent recovery of Benzoic Acid

Percent Recovery of Unknown

0.365 g x 100 = 36.5% 1.012 g 1.046 g x 100=52.3 % 2.011 g

Conclusion The melting point of a substance will determine the purity of a substance. For benzoic acid, the result of the melting point was 120-127°C and it was within the range of accepted values. For salicylic acid, the melting point was 155-160°C which was also within the range of accepted values. The reason why salicylic acid has higher boiling point than benzoic acid is because salicylic acid has higher and stronger intermolecular forces than benzoic acid. The percent recovery for benzoic acid was 36.5%. The starting material was 1.012g and recovered 0.365g of this substance. For the unknown the starting material was 2.011g with an ending material of 1.046g. The percent recovery of the unknown was 52.3%. The melting point of the unknown was 158.3-159°C being the accepted values for Salicylic Acid. The reason why recrystallization has lower percent recoveries is because this method is getting rid of impurities so its normal to have low percent yields. In addition, decanting errors play a role in low percent yields....