Name: Joshua B. Dacles Course & Year: BSChE – BSChE – 3 3
Date Performed: March 4, 2016 Date Submitted: March 11, 2016
Experiment No. 5 Melting Point of Solids
I. Objectives: 1. To determine the melting point of a solid substance. 2. To compare the results of experimental data to the literature data.
II. Theory: Melting point is the temperature at which a solid substance melts. It is also the temperature where the solid and liquid forms of a pure substance can exist in equilibrium. When heat is applied to solid substance, its temperature will also increase until its melting point is reached. As the heating process continues, more heat will then be able to convert all solid to its liquid form without changing the temperature.
The melting temperature of a solid is considered to be the same as its freezing point of its liquid form. Conversely, in actual practices, the freezing point of a liquid substance may not be equal to its melting point in solid form due to the characteristics of the liquid that enables it to freeze in different crystal structures and also when the liquid contains impurities which affect its freezing point. This temperature is a physical property of a solid which can be used to identify different substances. This physical property is used determine pure substances and elements. In actual situations, a solid will usually starts to melt over a range of temperatures rather than at one specific temperature. For example, when a substance melts over a small range of temperatures, the substance is assumed to be relatively pure, while on the other hand, if it melts over a wide range of temperatures, the substances is assumed to be relatively impure. When a range of temperatures is greater than 2˚, it is considered to be impure, and when we say impurities, these substances must be soluble in the solid because if not, they will have no effect on the melting point of the solid such as insoluble impurities like dust. Other than having a different range of temperatures, another way to determine whether a substance is pure or not is by knowing that impure solids melts at temperatures which are lower compared to that of the pure substance/compound. In general, an impure solid will melt over a wide range of temperatures and at a temperature lower than tha t of the pure solid. Nowadays, there are a number apparatus which are created to determine the melting point a solid substance. Some of these apparatus is the Mel-Temp device and Thomas Hoover Capillary Melting Point Apparatus. In this experiment, the latter is used, where the solid samples are placed in the capillary tubes and a nd is inserted into the apparatus.
III. Materials or Apparatus: A. Materials:
Vanillin, Acetanilide, Phenacetin, Sulfanilamide, Sulfapyridine, Caffeine B. Apparatus:
Thomas Hoover Capillary Melting Point Apparatus Capillary tubes Automatic Voltage Regulator
IV. Procedure: Prior to the experiment, four (4) unknown samples, in powder form, of about 1mm to 2mm in length were prepared by placing them inside the capillary tubes. The samples were labeled from number 1 to 4. We then, prepared the melting point apparatus and connected it to the voltage regulator in its 110V socket.
This was necessary because the electricity source available in the laboratory has 220V which is not suited for the apparatus that only needed 120V of electrical power. We also checked if both the equipments contains fuse to make sure they will function appropriately. After that we placed three capillary tubes into the melting point apparatus and switched it on. We then observed the powders inside the capillary tubes as the temperature rises inside the apparatus, and then we recorded the temperature at which the powders started to melt inside the tubes. For the two remaining samples, we used another Thomas Hoover melting point apparatus since there were two apparatus available in the laboratory and another reason was that because we must allow the apparatus to cool down after being used for the first samples so that the heat of the apparatus will not affect the measurement of the melting point of the new set of examples. The same process was conducted and then we recorded the corresponding melting point temperatures of the samples. After gathering the data that we needed, we then let the melting point apparatus to cool down by rubbing wet sponge on its walls to speed up its cooling time.
V. Diagram: Note: see attached page
VI. Data and Results:
Sample
Experimental (T)
Theoretical (T)
% Difference
1
162 ˚C
165 ˚C - 166˚C
1.81 %
2
134˚C
134.5 ˚C – 136 ˚C
0.37 %
3
110˚C
113.5 ˚C – 114.5 ˚C
3.08 %
4
79˚C
80.5 ˚C – 83.0 ˚C
1.86 %
5
234˚C
234.5 ˚C – 235.5 ˚C
0.21 %
VII. Computations: Sample 1: 165 −162
% Difference =
165
x 100 = 1.81 %
Sample 2: 134.5 −134
% Difference =
x 100 = 0.37 %
134.5
Sample 3: 113.5 −110
% Difference =
113.5
x 100 = 3.08 %
Sample 4: 80.5 −79
% Difference =
80.5
x 100 = 1.86 %
Sample 5: 234.5 − 2344
% Difference =
234.5
x 100 = 0.21 %
VIII. Observations and Discussions of Results: During the experiment I have observed that it was not simple to do the preparation of the samples to be used in the experiment. One must be patient in placing the powder form sample into the capillary tubes assigned to each of them. After we have gathered the needed materials and apparatus to be used, we first tested the melting point apparatus if it is working properly; therefore we tried to switch it on while being connected to a regulator whose voltage is 220V to a source with the same voltage.
We first switched on the power of the regulator and followed by the melting point apparatus but immediately after switching on the power of the apparatus, both the regulator and apparatus loosed power. Then, we checked the fuse of the equipments and found out that the fuse of the regulator was damaged while that of the apparatus was not. The reason behind was that the regulator should have a socket of 110V because the voltage needed by the apparatus was only 120V, so together with our faculty in the laboratory; we borrowed another regulator from the ECE department which is suited for the apparatus. After that, the apparatus functioned properly together with the voltage regulator. In this experiment, I have noticed that we should be a keen observer. One must have good eyesight in order to avoid errors in the data. The observer must be able to determine whether the samples in the capillary tubes will start to melt to know the correct temperature of the samples as their melting point. We also have noticed that while the temperature of the apparatus rises, its metal walls became hot as well that’s why we rubbed the walls with a wet sponge to neutralize the heat in the apparatus. After the experiment ended and gathered the melting point of the unknown samples, we searched the internet for the corresponding meting point of the solids mentioned in the materials on the 2nd page to determine the name of the samples we used. Then, the results were: Sample 1 = Sulfanilamide Sample 2 = Phenacitin Sample 3 = Acetanilide Sample 4 = Vanillin Sample 5 = Caffeine Basing from what we have searched, it showed that the sample 4 which has the lowest melting point is Vanillin with a melting point range of 80.5˚C to 83˚C and we obtained 79˚C as its melting point from the experiment. The caffeine turns out to be the sample 5 which in retort has the highest melting point among the samples given, 234.5˚C to 235.5˚C which is not quite different from what we obtained f rom the experiment which is 234˚C and has a percent difference of 0.21%. The melting point we obtained for the other samples had also very low difference as compared to their theoretical melting point. Sample 1 has a percent difference of 1.81%, 0.37% for sample 2, and 3.08% for sample 3. Since the theoretical melting point that were given to us were given in range of temperatures, we only used the lower range temperature to use as the comparison to the data that we have gathered.
IX. Conclusion and Recommendation: In this experiment, I can conclude that we were able to determine the melting point temperature of the different samples prepared correctly. The theoretical/literature data that were given to us does not have a big difference from what we have obtained experimentally since the percent difference of the melting point in the theoretical to its experimental data did not exceed above 5% . I can also conclude that the Thomas Hoover Melting Point Apparatus in the laboratory is functioning properly. The results were quite accurate and that is because the apparatus did its purpose correctly.
I recommend that in doing this experiment; make sure that the power source is suited for the apparatus to prevent accidents. If there were no suited socket for the apparatus, use a voltage regulator just like what we did in this experiment, but also take note that the regulator should also be suited for the apparatus because if not, the equipments may damaged and will not function properly which will results to error in the data later on. Lastly, I also recommend that the laboratory must have extra fuses just in case th e fuse will damage.
X. Applications: The main application of determining the melting point of a specific substance is to tell whether that substance is pure or otherwise. A pure substance generally has a melting range of one or two degrees. When impurities are present, they tend to broaden the melting range so the purified sample should have a higher and smaller meting point range that its impure sample. For example, melting point should be known so it can provide details about the purity of the substance where mixtures tend to melt at temperatures below the melting points of the pure solids.
Melting a solid, such as a metal or plastic piece, is an extremely valuable means of molding it into a desired a shape. The preparation of alloys involves the combining of metals after they have been melted. Melting is a way by which some of these substances in the solid can be separated from others. Materials with high melting points are valuable for making products that need to resist high temperatures.
XI. References:
http://www.chem.umass.edu/~samal/269/mp.pdf
http://www.britannica.com/science/melting-point
http://www.wiredchemist.com/chemistry/instructional/laboratorytutorials/determination-of-melting-point http://www.online-sciences.com/the-matter/what-is-the-melting-pointand-life-applications-on-melting-process/
