Another Source of error is limited data points that were observed. The thermometers used are also accurate. That is the melting point range for the sample. Based on the fact that mixture with 3-Ethoxy-4-hydroxybenzaldehyde had relatively close range of 76. Because melting point is a unique physical characteristic of a substance, melting point analysis does have high specificity. However, melting point is dependent on pressure as well, so experimental results can vary from literature values, especially at extreme locations, i. Fibers will remain in the melted B.
This sort of purity characterization cannot be performed if there are more than two primary components to the sample. Additionally, analysis requires small samples only. Compound was a volatile compound that changes from solid to gaseous form without going through liquid form sublimed. Eutectic mixture — mixture in which proportions of its constituents allow a uniform melting point for that mixture. Because melting point depression is unique between chemicals, a mixed melting curve comparing molar fractions of the two constituents with melting point needs to either be obtained or prepared. To characterize purity, first the identity of the solvent the main constituent of the sample and the identity of the primary solute need to be known.
Simply prepare standards with known molar fraction ratios, then perform melting point analysis on each standard and plot the results. Interpreting data There are two primary uses of melting point analysis data. Pure samples typically have a 1 - 2 °C melting point range, however, this may be broadened due to colligative properties. The biggest source of error stems from the visual detection of melting by the experimenter. Results and discussion Melting points for mixtures containing different percent of Naphthalene to Biphenyl were observed, recorded, averaged and graphed in Table 1 and Graph 1. Mixtures of Naphthalene and Biphenyl according to their mass percent used in experiment: 10% Naphthalene, 90% Biphenyl 30% Naphthalene, 40% Biphenyl 50% Naphthalene, 50% Biphenyl 70% Naphthalene, 30% Biphenyl 90% Naphthalene, 10% Biphenyl Values of melting points obtained in the observation were recorded in Table 1 and plotted into Graph 1. Non-pure samples exhibit melting point depression due to colligative properties.
A mixed melting curve for naphthalene and biphenyl. A magnification tool is attached to the machine to closely observe the material in the tubes. Based on the graph above eutectic point lies at 50% mole percent Naphthalene. Using melting point technique to identify mixture Unknown H was determined to be 3-ethoxy-4-hydroxybenzaldehyde. Most elements and compounds have a specific temperature at which it melts. Also, analysis is destructive of the sample. Average was taken from several results obtained by organic chemistry lab.
This may be done using other forms of analysis, such as gas chromatography-mass spectroscopy coupled with a database. For identification, compare the experimental melting point range of the unknown to literature values. Compare the melting point range of the experimental sample to the curve to identify the approximate molar fractions of the constituents. It has more substance to heat. Small amounts of whatever is tested is inserted into small, thin tubes and inserted into the machine. There are several vast databases of these values.
A melting point apparatus is a machine that helps chemists determine the identity of the compound based on what temperature it turns from a solid to a liquid. Pure substance has a sharp melting point with the maximum range of 5? Obtain a pure sample of the suspected chemical and mix a small amount of the unknown with it and conduct melting point analysis again. Conversely, if the melting point range is depressed or broadened, which would be due to colligative properties, then the unknown was not successfully identified. The first is for qualitative identification of the sample, and the second is for quantitative purity characterization of the sample. Also, samples with more than one solute cannot be analyzed quantitatively for purity. Average melting point specific to % Naphthalene in Naphthalene-Biphenyl mixture % Naphthalene inNaphthalene-Biphenyl mixture % Corresponding Melting point °C 0 68.
Once melting begins, note the temperature. Advantages of melting point analysis Melting point analysis is a quick, relatively easy, and inexpensive preliminary analysis if the sample is already mostly pure and has a suspected identity. Chem 211, Clark College 2007. Glass capillary to hold substance in a Melt Temp while heating. Class results were averaged, therefore one inaccurate result would effect the average point, this could be a potential source of error in the experiment.
Conclusion Melting point is a technique used to identify pure substances by observing ranges of melting points as it was done in mixtures of Naphthalene and Biphenyl. If a sharp melting point range is observed at similar temperatures to the literature values, then the unknown has likely been identified correctly. Clark, Organic Chemistry Laboratory: Standard and Microscale Experiments , 2 nd Edition, Saunders College Publishing, San Diego 1997. . Using procedure for melting point determination with Mel-Temp on p. This is device is a tool used in the determination of the identity and purity of a sample.
Visually inspect the sample as it heats. Compounds depending on their chemical structure have a specific melting point. Eutectic point, however, should be kept in my when testing for pure substances, for eutectic compositions can mislead results of the test if nothing else is considered. Specificity and accuracy Melting point analysis is fairly specific and accurate given its simplicity. Residual recrystallization solvent —mostly contains water, which would lower the melting point of B. Results are reported in Table 2.
Controlling the change rate and running multiple trials can lessen the degree of error introduced at this step. Due to the big difference in melting points between substances, glass will stay insolvent. Melting Point Diagram for Naphthalene and Biphenyl. Mixture that had sharp melting point was mixture that contained identical parts. When the sample is completely melted, note the temperature again. Two known samples with the closest to unknown H mps were determined.