Experiment 1 Lab PDF

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Experiment 1: Melting Point Determination

Abstract The melting point of a substance is the temperature at which it changes from solid to liquid at atmospheric pressure. There are multiple factors that influence the melting point of a pure substance including how tightly molecules pack together, molecular size, and electrostatic forces between molecules. Impure solids, like Urea in this experiment, tend to have lower melting points than their pure counterpart. If a melting point is sharp, it is a good indication that the solid is pure. However, if the melting point is over a wide range, it is most likely that the solid is impure. The purpose of this experiment is to determine the melting point of the unknown and determine what the substance is by comparing it to the melting points of the known solids. After taking the melting point of the unknown twice, it had a melting point between 133C135C which is close in measurement to Urea and trans-Cinnamic Acid which have melting points between 132C-133C. When mixing the unknown with Urea, the melting point had a differential that was too big to be the unknown. The melting point was 130C- 134C when mixed with Urea. However, when mixed with trans-Cinnamic Acid, the melting point was relatively the same, 134C-136C, making it certain that the unknown was trans-Cinnamic Acid. MSDS 

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Acetanilide o Chemical Formula: C 8 H 9 NO o State: Soild o Molecular Weight: 135.17 g/mol Health: 3 o Boiling Point: 304C (579.2 F) Fire: 1 o Melting Point: 114.3C (237.7 F) Reactivity: 0 3 o Density: 1.22 g/cm o Hazards: Substance is an eye and skin irritant. Harmful if ingested and can cause respiratory tract irritation. Fluorene o Chemical Formula: C13 H 10 Health: 1 o State: Soild Fire: 1 o Molecular Weight: 166.22 g/mol Reactivity: 0 o Boiling Point: 295C (563F). o Melting Point: 114.76C (242F) o Density: 1.2 g/cm3 o Hazards: Substance is an eye and skin irritant. Harmful if ingested and can be a respiratory tract irritant Mandelic Acid Health: 3 o Chemical Formula: C 8 H 8 O 3 Fire: 1 o State: Soild Reactivity: 0

Molecular Weight: 152.15 g/mol Boiling Point: 321.8C (611.2F) Melting Point: 119C (246.2F) Density: 1.3 g/cm3 Hazards: Substance is a skin and eye irritant. May cause digestive tract irritation and respiratory tract irritation. Benzoic Acid o Chemical Formula: C7 H 6 O 2 Health: 2 o o o o o

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State: Soild Fire: 1 Molecular Weight: 122.12 g/mol Reactivity: 0 Boiling Point: 249.2C (480.6F) Melting Point: 122C (252F) Density: 1.27 g/cm3 Hazards: Substance is a severe eye irritation and skin irritation. Harmful is ingested or inhaled. 2-Naphthol o Chemical Formula: C10 H 7 OH Health: 2 o State: Solid Fire: 1 o Molecular Weight: 144.17 g/mol Reactivity: 0 o Boiling Point: 285C (545F) o Melting Point: 122C (251F) o Density: 1.22 g/cm3 o Hazards: Substance is an eye and skin irritant. Fatal if inhaled and harmful if ingested. Urea NH Health: 1 ¿ o Chemical Formula: CO ¿ Fire: 1 ¿ Reactivity: 1 o State: Solid o Molecular Weight: 60.06 g/mol o Boiling Point: 196.6C (385F) o Melting Point: 134C (273F) o Density: 1.32 g/cm3 o Hazards: Substance is an eye and skin irritant. Harmful is inhaled or ingested. Trans-Cinnamic Acid o Chemical Formula: C 9 H 8 O 2 Health: 2 o State: Soild Fire: 1 Reactivity: 0 o o o o o o

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Molecular Weight: 148.16 g/mol Boiling Point: 300C (572F) Melting Point: 133C (272F) Density: 1.25g/cm3 Hazards: Substance is a skin and eye irritant. May cause digestive tract irritation and harmful is inhaled Benzoin o Chemical Formula: C14 H 12 O 2 o o o o o

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o State: Soild Health: 1 o Molecular Weight: 212.25 g/mol Fire: 1 o Boiling Point: 344C (641F) Reactivity: 0 o Melting Point: 136C (275F) o Density: 1.31 g/cm3 o Hazards: Substance is a skin and eye irritant. Harmful if ingested or inhaled Maleic Acid o Chemical Formula: C 4 H 4 O 4 Health: 3 o State: Solid Fire: 0 o Molecular Weight: 116.07 g/mol. Reactivity: 0 o Boiling Point: 202C (396F) o Melting Point: 135C (275F) o Density: 1.59 g/cm3 o Hazards: Substance is a skin and eye irritant. Harmful if ingested or inhaled. Procedure

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Step One Prepare two capillaries containing the unknown, you cannot reuse a spent melting point capillary tube. The first melting point can use using the melting point apparatus with a heating rate of about 10 degrees per minute to give a ball park figure. Then let the thermometer and melting point apparatus cool to at least 20 degrees below this approximate melting point and use the second packed capillary tube to obtain an accurate melting point with a heating rate of no more than 2 or 3 degrees per minute. Step Two From the melting point of the unknown, decide which of the listed of compounds it might be. Compound Melting Point (C) Acetanilide 113-114C Fluourene dl-Mandelic Acid

114-115C 117-118C

Benzoic Acid 2-Naphthol Urea

121-122C 121-122C 132-133C

Trans-Cinnamic Acid Benzoin

132-133C 136-137C

Maleic Acid

136-137C

Prepare a mixture of the unknown with the compound that is the most likely to be the unknown and take the melting point of this mixture. If the melting point is the same, it is most likely that the unknown and the compound mixed with it are the same. If the melting point of the mixture is lower, choose a different known and try again until the melting point isn’t lower than your unknown. Data Calibration of Melting Point Apparatus Using trans-Cinnamic Acid M.P. in apparatus M.P. Literature Difference Value 133ºC-134ºC 132º-133º 1ºC 133ºC-134ºC 132º-133º 1ºC

Trial 1 2

Trial 1 2

Mixture Unknown + Urea Unknown + trans-Cinnamic Acid

Melting Point of Unknown Melting Point 133º-135ºC 133º-135ºC

Determining the Unknown Melting Point 130ºC-134ºC 134ºC-136ºC

After Calibration 134ºC-136ºC 134ºC-136ºC

After Calibration 131ºC-135ºC 135ºC-137ºC

Notes/Observations In the lab manual, it stated that there would be 8 knowns that the unknown could have been. However, in the actual lab, there were only 4 knowns. The urea compound was impure which caused a lower melting point than it’s literature value. Trans-Cinnamic Acid had an offset of 1ºC when the apparatus was calibrated.

Calculations Calibration difference= Actual value- Literature value Trial 1 Calibration= 134 ºC - 133 ºC = 1ºC Trial 2 Calibration=134 ºC - 133 ºC = 1ºC Conclusion The melting point of the unknown fell in between the range of 133ºC -135ºC which led to the possible compound to either be Urea or trans-Cinnamic Acid which both had a melting point of 132ºC-133ºC. When Urea and the unknown was mixed, the melting point of the mixture was 130ºC-134º. However, when the unknown was mixed with trans-Cinnamic Acid, the mixture had a melting point of 134ºC-136ºC. Trans-Cinnamic Acid had to be the unknown because the mixture’s melting point couldn’t be lower than the original melting point of the unknown. The reason Urea had a lower melting point when mixed with the unknown was because it wasn’t a pure Urea compound. Pre and Post-Lab Questions 1.) True or False Question: The melting point of a pure, solid compound with weaker intermolecular interactions would be expected to have a relatively lower, but sharp and not depressed, melting point Answer: True Question: Heating a melting point sample too quickly can lead to an inaccurate melting point, either higher or lower than the actual melting point, depending on the apparatus. Answer: True 2.) If your compound A is contaminated with solvent when you take a melting point and the literature value melting point of compound A is 120ºC to 122ºC, then what would you expect for your melting point in this situation? I would expect the melting point to be lower than its stated literature value due to contamination. 3.) If you heat too fast, will your observed melting point be higher or lower than the true value?

Heating too fast would cause the melting point to be higher than it’s true value. 4.) Draw the structure of naphthalene and sulfanilamide and provide their literature melting points. What factors influence their respective melting

points? Naphthalene M.P: 80.26ºC

Sulfanilamide M.P: 165ºC

Melting points are affected by multiple factors including molecular size, how tight molecules are packed together, and their intermolecular attraction....