CHE 223 - Melting Point Lab PDF

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The abstract is the only thing that I got points deducted for. Overall score 90/100....

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Determining the Melting Points for Urea, Cinnamic Acid, Urea + Cinnamic Mixtures, and an Unknown Substance Name: Karina G. Garcia Partners Name: Ava Glahn Date Performed: September 13, 2021 Date Submitted: September 20, 2021 Abstract: Within this lab we will be observing the different melting points between samples of pure organic compounds of Urea, Cinnamic Acid, fixed mixtures between the two, and an unknown. To do so we will be working with the Melting-Point Apparatus that will help us observe when the samples are melting and their respective temperature at which it is occurring. As seen in the results for the mixtures, two of the mixtures melted at the same temperature disregarding their percent composition leading to question the purity of the samples and accuracy of the readings. Objective: To understand different organic molecules intermolecular attractive forces by observing their physical properties, such as melting point and boiling point. Introduction: Organic Compounds have identifying properties that help classify them based on their composition. Melting points and boiling points are two physical properties that can help identify these compounds. Melting points are used to: (1) characterize a known sample, (2) to allow future characterization of new samples, and (3) to determine the purity of the compound. In knowing an organic compound's melting point, it can be later used in the process of identifying unknown organic compounds and to learn about their intermolecular attractive force. In this lab we will observe the meting point of two known samples, Urea and Cinnamic Acid, mixtures between the two, and an unknown sample. To do so we will be using the Melt-Temp apparatus which ill not only heat up and melt our sample but allows us to observe this process while noting the temperature. In recording the melting temperature, two temperatures must be noted, the point at which the first drop of liquid formed among the solid sample and the point at which the whole mass of the sample turned into a liquid. These solids have a crystal lattice, which is their definite repeating pattern that influences the nature of the solid. The melting point theory states that in order to break these forces a specific amount of energy, in this case heat, is required. Therefore, the amount of heat required to change a substance from solid to liquid phase, or the melting point, is a property that can be used to establish a crystalline’ s identity and purity.

Materials:

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Thermometer – used to observe the samples melting temperatures Melting Point Capillaries – used to hold sample Urea (s) (Pure Sample) Cinnamic Acid (s) (Pure Sample) Unknown Sample (s) Metal Spatulas – used to collect sample Melting Point Apparatus – used to observe and melt samples

Table of Physical Constants: Name

Structure

Molecular Weight (g/mol)

Molecular Formula

Boiling Point (oC)

Melting Point (oC)

Density (g/cm3)

Solubility

Urea

60.056

CH4N2O

150

132.5-133

1.32

Soluble in water and ethanol

Cinnamic Acid

148.15

C9H8O2

300

132.5-133

1.25

Soluble in water

Apparatus:

Procedure and Observations:

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Procedure Urea and Cinnamic Acid 1. Samples of Urea and Cinnamic Acid were prepared. 2. Melting-point capillaries were filled with the samples. 3. Melting-Point apparatus was plugged in and began to heat up. Since the melting temperature is known, the apparatus was heated until 20oC below the melting point. Then the melting point should increase no more than 1oC per minute as the sample is melting. 4. Record and observe when the samples begin to melt. Urea and Cinnamic Acid Mixtures 1. Using a metal spatula, samples of Urea and Cinnamic Acid mixtures were collected in the approximate proportions (Urea: Cinnamic Acid) 1:4, 1:1 and 4:1. 2. Melting-point capillaries were filled with the fine powder mixtures. 3. Melting-Point apparatus was heated and the ranges of melting from the three mixtures were noted. 4. Temperatures of complete liquefaction were used to create a diagram of melting point vs. composition. Unknown Sample 1. Capillary for the unknown sample supplied was prepared. 2. Melting-Point apparatus was heated while determining the approximate melting point. 3. Note the melting point temperature and refer to table 3.1 to identify the unknown sample. Flow Chart:

Observations Samples were already pre-crushed. Filled the capillary with approximately 1 cm of the sample. First began with Cinnamic Acid and it started melting at 115oC and was fully melted at 130oC. Urea started melting at 122oC and was fully melted at 130oC.

Mixtures were already pre-made in 25:75, 50:50, and 75:25 proportions. 25:75 Urea + Cinnamic Acid mixture started melting at 75oC and was fully melted at 95oC. 50:50 Urea + Cinnamic Acid mixture started melting at 80oC and was fully melted at 90oC. 75:25 Urea + Cinnamic Acid mixture started melting at 99oC and was fully melted at 107oC.

Unknown sample no. 24 Unknown sample started melting at 89oC and was fully melted at 112oC. Unknown sample was determined to be Acetanilide

Garcia 4 Calibrate thermometers  Prepare samples  Fill capillary tube with each sample, one at a time  Place capillaries, one at a time, in the Melt-Temp apparatus  Record the temperature in which the liquefication Waste Disposal: ● Do not place leftover substances down the sink ● Place all used samples in a waste container Safety Precautions: ● Care should be taken to not break the thermometer, which will release the toxic mercury ● All procedures involving volatile and/or flammable solvents should be conducted under a flame hood Results and Discussion: Throughout the lab, several melting points were collected while observing how these pure organic samples and mixtures were being melted. For the first part of the experiment the melting temperature collected for Urea was 126oC and Cinnamic Acid was 122.5oC. Both of these melting points are less than 10oC away from the actual melting point. These varying results can be due to human error when trying to observe when the substance liquefied while checking the thermometer, simultaneously. Another reason could have been improper cooling of the MeltingPoint apparatus in between samples. For the second part of the experiment, melting point for Urea: Cinnamic Acid mixtures was recorded. Based on the recordings shown in the graph below, for the 25:75 and 50:50 mixtures the melting points were both at 85oC while the 75:25 mixture had a higher meting point at 103oC. The difference in melting points can be accounted for by the variation of percent composition from each mixture. The similarity between the 25:75 and 50:50 sample could be accounted by human error while preparing the sample, using the Melting-Point apparatus, or the closeness in percent composition. Lastly when determining the melting point for the unknown sample no.24, it was noted that the approximate melting temperature 100.5oC. To identify the unknown, we must compare our results to Table 3.2 Melting Point Unknowns (Williamson & Masters, 2011) where the closest compound is Acetanilide. Although far from the 13.5oC-114oC melting point for Acetanilide, it is above the melting points for Naphthalene leading us to that conclusion.

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% Composition vs. Melting Point 120

Melting Point (C)

100 80 60 40 20 0

% Compositon (Urea: Cinnamic Acid)

Conclusion: From the three experiments performed during lab, many melting points for different organic compounds and mixtures were recorded. It was noted that the 25:75 and 50:50 Urea: Cinnamic Acid mixtures had a similar melting point, even though the percent composition should have prevented this. In the Unknown sample experiment, sample no. 24 was identified to be Acetanilide due to the closeness of our results and the information provided in Table 3.2 Melting Point Unknowns. References: Williamson, K.L.; Masters, K.M. Macroscale and Microscale Organic Experiments, 7th ed.; Cengage Learning: MA, 2011 Urea. https://pubchem.ncbi.nlm.nih.gov/compound/urea (Accessed September 12, 2021) Cinnamic Acid. https://pubchem.ncbi.nlm.nih.gov/compound/cinnamic-acid (Accessed September 12, 2021)...