Lab report (melting point) PDF

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This is a lab report that was completed and submitted to TA. I received 100% on the assignment....

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Selina Karim 2694784 Experiment Title: Melting Point Lab Partners: Samantha and Mackenzie Goals: 1. To observe the proper method of obtaining melting point. 2. To identify an unknown organic substance using it’s melting point. Pre-Questions: 1. In the experiment, the melting points obtained were ranges rather than a single unit. 2. The unknown organic compound would have been cinnamic acid if the mixture melted at the same temperature as the unknown. 3. Some of the substances appeared to be purer than others because some of their melting point rangers were narrower than others. 4. The melting point of the mixture decreased, which revealed that the substance was urea. 5. Impurities lower the melting point of compounds, which was a key point in helping us determine the identity of the unknown substance in step 4. Procedure: C.1: Six chemicals were placed in the melting point apparatus to observe their melting point ranges. Each substance was observed two times in order to minimize any errors that may have occurred. The experimental values were used to calculate the correction factor compared to the actual melting points of each substance. C.2: An unknown organic substance was obtained. Using two trials of obtaining melting point, the identity of the organic compound was obtained by comparing the experimental values to the actual melting point values of organic substances. C.3: A vial of an unknown substance and a cinnamic acid solid was obtained. They were mixed together and melted to obtain the melting point of the mixture. The range would be cinnamic acid if it was consistent with the original melting point range of the experimental cinnamic acid. If the melting point range was lower for the mixture, it is deemed urea. Observations: 1. The correction factor of cinnamic acid was the highest at -4. 2. Unknown B is m-dinitrobenzene with a melting point range of 91-93C. 3. The unknown substance in part 3 was urea due to a decrease of 10C from the melting point of cinnamic acid compared to the melting point of the mixture.

Results Name of Chemical

Observed Melting Point Range 53-57C

Observed Melting Point 54-55C

Correction Factor

Diphenylamine

Actual Melting Point 53C

m-Dinitrobenzene

90C

90-91C

90-91C

-0.5

Benzoic Acid

122C

121-126C

121-126C

-1.5

Cinnamic Acid

133C

138-141C

136-138C

-4

Salicylic Acid

159C

157-160C

158-161C

-0.5

3, 5 Dinitrobenzene

205C

204-207C

204-205C

+0.5

C.1:

Experimental Melting Point Vs. Correction Factor Correction Factor

1 0 40 -1

60

80

100

120

140

160

180

-2 -3 -4 -5

Measured Melting Point (C )

C.2: Melting Point (C) Trial 1 91-94C Trial 2 91-93C C.3: Melting Point (C) Unknown 132-133C Mixture 122-125C

200

220

-1.5

Discussion: The melting point range is the range of points at which a solid will melt into a liquid (a phase change). The melting point of a substance can help identify an organic compound and determine this substances purity. Calibrating the thermometer because a thermometer can become inaccurate at different temperatures if not calibrated. Calibration is important because it will ensure that accurate results are obtained and errors are minimized. In part one of the experiment, six substances were melted to determine their melting point ranges and compared to the known values that each substance melts at. The correction was obtained and plotted against the the observed melting point values (as shown in the graph above). In part two of the experiment, an unknown solid was obtained and melted to determine its melting point range(91-93C). This information was compared to the known melting points of substances and it was determined that m-dinitrobenzene was the unknown substance. In part three of the experiment, an unknown substance was obtained. The substance was either urea or cinnamic acid, both with a melting point of 133C. The unknown substance was mixed with cinnamic acid and they were melted to find the melting point of the mixture. Since the mixtures melting point was 10C lower than the melting point of cinnamic acid, the substance was identified as urea. One problem that was encountered was with the melting point apparatus. In the first few trials of part one, the apparatus could be set to the melting point, therefore the increase in temperature was slower than normal. Conclusion: The experiment was successful because we were able to understand how the melting point of a substance can be measured. The unknown substance in part two was correctly identified as m-dinitrobenzene. The correction factors for all of the substances were relatively low and this difference could have been due to the apparatus not peaking or an impurity developing in the substances due to exposure. In part three of the experiment, the melting point dropped 10C, which helped identify the unknown substance as Urea and not cinnamic acid. If the substance was cinnamic acid, the melting point would have remained the same. References: Mohrig, J.R.; Alberg, D.G.; Hofmeister, G.E.; Schatz, P.F.; Hammond, C.N.; Laboratory Techniques in Organic Chemistry; Freeman, New York, 2014, 62 – 63 and 211-220 Schoffstall, A.; Gaddis B.; Drueling, M.; Melting Point; Microscale and Miniscale Organic Chemistry Laboratory Experiments, McGraw-Hill, (2011), 22-7....