Melting+Points+Laboratory+Report

__**Melting Points Laboratory Report**__ October 1, 2010 Merissa Honey Kerry Gillette

__**Introduction**__ //Question of the Day: What can we learn about a sample by measuring its melting point?// The purpose of this laboratory activity is to practice the necessary techniques and to predict and observe differences in melting points of pure and mixed substances. Finding the melting points of pure and mixed substances help identify unknown substances, as laboratory data can be compared to known values to identify a substance. Melting points can also indicate the level of purity of a substance, because pure substances have a very narrow melting point range. If a substance has a melting point range that is wider than 5 deg. C, it is most likely impure. Mixtures tend to have melting points that are lower than the melting point of a pure substance. Different solids melt at different specific temperatures therefore after finding the melting point, one can identify the substance. This technique entails isolating a finely ground sample of a solid substance, transferring a small portion into a melting point capillary tube, placing it into a melting apparatus such as a MelTemp, slowly increasing the temperature and recording when the sample begins to melt (known as sweating) and finishes melting. After comparing the melting points of mixtures of compounds and individual substances, the laboratory students will recognize how useful melting point measurements are. Nice job on this section!!!

1. The melting point of 1-indanone was measured and recorded two times using melting point capillary tubes and a MelTemp apparatus. 2. 0.20g 1-indadone (0.195g was measured) and 0.25g 3,4-dimethoxybenzaldehyde (Exactly 0.25 g was measured) were measured and placed in a beaker where they would later be crushed and mixed. Careful! Are you reporting data here (like your measurement) or telling me what the procedure is? If it is the first, why do I only get the actual mass for the first substance? 3. A prediction was made regarding the melting point of the mixture and whether the temperature would increase or decrease. Some suggested possible results of what might take place when substances were mixed were: melt at room temperature, have a higher temperature than either of the pure substances' individual melting points, cover the entire range, or that the melting point is proportional. 4. The two substances were then crushed and mixed thoroughly using either a glass rod or a spatula. Observations of the mixture were then noted. 5. 0.05g NaOH was added to the beaker, mixed for five minutes, and then allowed to rest for ten minutes. 6. 2mL of 10% HCl was added to the beaker via pipette, the mixture was mixed using a glass stir rod, and the pH was tested using litmus paper to ensure that it was acidic. The mixture was transferred to an aspirator, and the solid collected via vacuum filtration. The solid was then transferred to a crucible, and dried in a drying oven for 8 minutes. //__Note:__// At this point in the lab, the problem of not being able to vacuum filtrate the mixture was encountered. This was because it did not mix, rather it stayed as two separate substances; one like gel and the other a liquid. It was decided that the lab be to start the lab over again from this point. In order to ensure that the mixture would mix well, caution was taken with the amount of NaOH added. It was found that the more NaOH added, the better mixture took on a better consistency in preparation for vacuum filtration. Lastly, the melting point of the dried solid was then measured using a melting point capillary tube and a MelTemp apparatus.
 * __Procedure__**
 * __Part 1:__**

1. The melting point of pure urea was measured and recorded using a melting point capillary tube and a MelTemp apparatus. 2. It was predicted that pure urea would have a higher melting point than the mixture, in accordance with the data observed in part 1, as the mixture of I-Indanone and 3,4-dimethoxybenzaldehyde had a much lower melting point (prior to the addition of NaOH). 3. A mixture of 2:5 urea to cinnamic acid was mixed, and the melting point measured and recorded. 4. A mixture of 5:2 urea to cinnamic acid was mixed, and the melting point measured and recorded.
 * __Part 2:__**

The lab station and materials were then cleaned.

Chemical reaction of two substances involved in part 1:
 * __Data__**

I am so happy to see that you have included the reaction, even if you don't understand the details!


 * > **Temperature in Celsius** ||> **1-Indanone a** ||> **1-Indanone b** || **3,4-dimethoxylbenzaldehyde**
 * (Average temperatures written on the board)** ||> **1-Indanone and 3,4-dimethoxylbenzaldehyde product** ||> **pure Urea** ||> **Urea:Cinnamic acid**
 * 2:5** ||> **Urea:Cinnamic acid**
 * 5:2** ||
 * > **Starting temp** ||> 21.6 ||> 32.5 ||  ||> 22.2 ||> 60.7 ||> 73.3 ||> 73.3 ||
 * > **Sweating temp** ||> 37.7 ||> 37.8 || 39.9 ||> 125.1 ||> 128 ||> 98.9 ||> 98.9 ||
 * > **Melting temp** ||> 40.1 ||> 41.1 || 44.3 ||> 167.3 ||> 136.3 ||> 102.5 ||> 128.1 ||

Part 1: 1-indanone, a yellow, chunky crystalline substance, when combined with 3,4-dimethoxylbenzaldehyde, a rosy-yellow flaky substance, melted into a clear, yellow liquid with some light colored solid flakes at the bottom. As a mixture, the two combined at room temperature into a liquid. This change occured without any apparent chemical reaction taking place (no change in temperature was felt, no visible gases were given off, no color change was observed, nor were any other indicators that a chemical reaction had taken place were seen). Upon the addition of NaOH, the substance became increasingly opaque, and a solid was formed after the five minutes of stirring, and ten minutes of resting. HCl was added to ensure the removal of any residual base, and upon mixing, the solid broke into flakes that were distinctly separate from the HCl and appeared to be light yellow. The pH was noted as acidic using litmus paper, and the solid dried in the dryer. The melting point of this solid product was significantly higher than the individual melting points of the reactants.
 * Observations:** Observations are important, too. Thanks for including them.

Part 2: The pure urea looked like small round white balls, and was crunched up into powder for the experiment. The cinnamic acid was a white powdery substance. It was observed that the melting point of pure urea was higher than the melting point of the mixtures, however, the mixture with the higher ratio of urea had a closer melting point to the pure urea than the mixture with the lower ratio of urea.


 * __Data Analysis__**

Part 1: The melting points from trials 1 and 2 are within the appropriate melting point range for I-Indanone: 38-42 deg. C. Sources of error included difficulty visually specifying when melting had begun and ended, as the eye piece on the apparatus is rather narrow and although magnified, viewing with certainty was tricky. Also, the finalized interpretation of the temperature on the MelTemp because the temperature appeared to fluctuate up and down. At first attempt, adding NaOH did not yield the intended solid. Instead, what was observed was an "oiling out," in which the compound gained a green gelly,oily appearance, which did not solidify. This could have been caused by several things: incomplete dissolving of the initial two compounds (some of the substances stuck to the sides of the beaker and therefore did not fully react in the reaction,) the addition of too much NaOH, and impurities in the compound. All of these could have accounted for as errors that threw the temperatures off but not enough to alter the final conclusion. The observed results are in alignment enough to see the major direction or expected trend that occurred. The second trial was successful, perhaps due to a lesser amount of NaOH added. It was hypothesized that the product would slightly raise the temperature, however, the data indicates that the product has a much higher melting point than the initial two products. This indicates that a chemical reaction took place, in which the product is an entirely different compound than the reactants. The experimental results gathered in the lab mostly agree with the commonly expected values, but are not exact. Part 2:

The data indicates that the melting point of a pure substance will be higher than the melting points of the components combined to produce it. The more urea in the mixture, the closer the melting point was to that of the pure substance. A source of error was the difficulty crushing the small balls of urea, as they tended to pop apart when smashed, sending small pieces flying. The initial amount of urea gathered was almost exactly the amount specified, however, the final true amount of urea included in the mixture was most likely less than what was there originally. Based on the data gathered, it can be concluded that comparing the melting points of a substance with the individual components used to make it can show whether a reaction took place, along with the purity of each of the substances used. The experience with "oiling out" also provided an excellent lesson in the unexpected challenges that appear during laboratory activities. very nice! Sources: background information on melting point errors and "oiling out" phenomenon: [] [] This video provides general information and guidelines for this lab: []

Post Lab question: 0.3g unknown substance provided Melting point of substance A: 83.0 deg. C Melting point of substance B: 83.1 deg. C Which substance is the unknown? How could it be identified?

Possible method: One could construct an experiment that mirrors part 2 of the above experiment. It is known from the previous experiments that a mixture has a lower melting point than the pure substance. If a 1:1 mixture of the unknown was made with both substances A and B, conceivably, the mixture which does not match would have a much lower melting point than the mixture that did match. The matching mixture would have a melting point very close to 83.0-83.1 deg. C. If the data values were still too close, more elaborate ratios could be used, such as: 2:5 Unknown to A, 5:2 Unknown to A 2:5 Unknown to B, 5:2 Unknown to B

The mixture that matches should consistently melt at the expected range (because it would consist of a relatively pure substance). The incorrect mixture should yield a range of melting points, similar to the Urea-Cinnamic Acid activity. good.