Determination of Melting and Boiling Point of different Organic Compounds Bakare, Abimbola Kristine, C.
Professor Miranda Marilyn, school of chemical engineering and biotechnology, Mapua Institute of Technology, CHM145L-B11
A melting point of a solid is the temperature at which the first crystal just starts to melt until the temperature at which the last crystal just disappears. Thus, the melting point (m.p.) is actually a melting range. The melting point of a substance depends (usually slightly) on pressure and is usually specified at standard pressure. The boiling point of a substance is the temperature at which the vapor pressure of the liquid equals the pressure surrounding the liquid and the liquid changes into a vapor. In this experiment we were be able would use various apparatus to determining the melting point and boiling point of organic compounds. We realized that boiling point and melting is affected by pressure, molecular weight, structure, intermolecular interactions and most of all impurities present in the compound.
The melting point of a substance is the temperature at which the material changes from a solid to a liquid state. Pure crystalline substances have a clear, sharply defined melting point. During the melting process, all of the energy added to a substance is consumed as heat of fusion, and the temperature remains constant. A pure substance melts at a precisely defined temperature, characteristic of every crystalline substance and dependent only on pressure (though the pressure dependency is generally considered insignificant). Determining the MP is a simple and fast method used in many diverse areas of chemistry to obtain a first impression of the purity of a substance. This is because even small quantities of impurities change the melting point, or at least clearly enlarge its melting range. The boiling point of a liquid is the special case in which the vapor pressure of the liquid equals the defined atmospheric pressure at sea level, 1 atmosphere. At that temperature, the vapor pressure of the liquid becomes sufficient to overcome atmospheric pressure and allow bubbles of vapor to form inside the bulk of the liquid. The standard boiling point is now (as of 1982) defined by IUPAC as the temperature at which boiling occurs under a pressure of 1 bar. During this experiment there were a lot to consider because there are factors influencing the boiling point and melting point of an organic compound. 1.) ION-ION FORCES
These forces or attractions are the strongest. They involve the attraction between species bearing at least a full positive charge and a species bearing at least a full negative charge. The species involved can be simple ions (Na+CI-) or complex ions ((NH4)+(CH3CO2)-). In the latter case, the charge is held by a covalently bound species. For example, the atoms within (CH3CO2)- are covalently bound, but the overall structure possesses a net negative charge. Fully charged species are so attracted to each other that they can get very close and form extensive ion networks.
2.) Dipole-Dipole Forces
Dipole-dipole forces are considerably weaker than ion-ion forces, but if significant, can have a large influence on physical properties. Dipole-dipole forces are important for molecules having net dipole moments, i.e., molecules having atoms with differing electro negativities arranged in such a way that the center of positive charge is different from the center of negative charge. In other words, the electron cloud is distorted so that an area(s) of the molecule is richer in electron density and another area is depleted of electron density. When in close proximity, the molecules will align themselves in such a way that the poles are complementary, i.e., δ+ with δ - and δ - with δ +.
Strong dipole-dipole interactions, usually involving the hydrogen (δ+) on an oxygen, nitrogen or fluorine interacting with another...
Please join StudyMode to read the full document