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A full lab report in organic chemistry on a melting point leb
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Lexa Marchese 7/25/ Chem 315- I Objectives
II Theory Melting point is the temperature at which a solid melts to become a liquid.^1 Melting point is a physical property that can be used to identity a substance and its general purity. Purity is the degree to which a substance is undiluted or unmixed with extraneous material, typically expressed as a percentage.^2 We can tell if there is impurities by how wide the range is in a melting point, the larger the range the more impurity there is. Melting point is used for identification because most compounds usually do not have the same melting point. Melting point is like a finger print, each compound has a different one that can make them easily identifiable.A more specific definition for melting point is the temperature at which the solid exists in equilibrium with its liquid under an external pressure of one atmosphere.^3 Factors that affect melting points are size of a molecule, shape of molecule, and intermolecular attractions. The size of a molecule affects the melting point because when molecules are smaller and polar they melt at lower temperatures because there bonds are not as strong. Also the melting point gets lower as the polar molecule gets larger because its bonds are not as stable, more compact bonds are harder to break and the larger the molecule the less compact. However, if ionic compounds are present in a smaller molecule it makes its melting point higher than a large molecule with ionic bonds because the smaller molecule can get more compact and form more stable bonds. The shape affects the melting point because if the molecule allows itself to be very tightly compacted it will have a higher melting point. The less compact a molecule, the lower the melting point because it is not as stable so the bonds are easier to break. This is why symmetrical compounds usually have a high melting point because they are more stable and compact. Lastly, intermolecular attractions affect the melting point. Covalent bonds are weaker than ionic bonds, so compounds with covalent bonds usually have a lower melting point than those with ionic bonds. But in other cases if the compound that has covalent bonds has polar bonds as well the electronegativity of the atoms then causes the melting point to be higher than
Urea NH 2 CONH 2
g/mol
g/cm^3 135 o-139o^ N/A 133 oC Highly toxic, flammable IV Procedure Reference CHEM 315- Organic Chemistry I Lab Laboratory Manuel, Fall 2017, Dr. John K Berch, Jr. Lab 2- Melting Point V Observations
beginning there melting point process and both completely melting at around 139oC. The 50:50 mixture of Cinnamic Acid and Urea had a melting point range of 102oC-115oC. It began melting at 102oC and had completely melted by 115oC. Unknown 1 had a range of 105oC-125oC. It began to sweat at 105oC and completely melted at 125oC. Unknown 2 had a range of 210oC-243oC. It began to melt at 210oC and was completely melted by 243oC. Cinnamic Acid and Urea melting points found in the lab were a little above there actually melting points showing some lab error. The samples were first put into bowls before the lab so they could have absorbed moisture causing some impurities. This could also be the case for the two unknowns. Since there melting point ranges were very spread out it shows impurities due to lab error. Another error in lab that could have occurred was someone not watching the sample every second so it began to melt before someone caught it. The 50:50 mixture of Cinnamic Acid's and Urea's range was signicantly lower than the melting points of the two indivual substances which shows the mixture has impurities. But since it was a mixture of the two substances it was expected that it would melt at a lower temperture and have a larger range. The difference in melting point and range shows how sensitive melting points are and how easily they change when exposed to impurities. When indentifying the 2 unknown substances we had to compare melting points and the known boiling points found in research done for this report against the 4 possible substances: Acetanilide, Caffeine, Cinnamic Acid, and Urea. When looking at the melting point for unknown 1, which was 105 oC-125oC, we can confer that it must be Acetanilide because its actually melting point is 114.3oC and its actual melting point is the closest in range to Acetanilide. The other substances melting point go to high for it to be them. Unknown 2 having an experiemental melting point 210oC-243oC shows to be Caffeine because Caffeine has an actual melting point of 235oC. None of the other substances even come close to having such a high melting point, so ruling them out was the easiest. Though the melting points differ, we can conclude that unknown 1 is Acetanilide and unknown 2 is Caffeine because there
