To learn how to obtain an accurate melting point using a MELTING POINT APPARATUS, then use them to draw eutectic curve and determine the eutectic point. Melting point of a solid is the temperature at which the solid and its liquid form are in equilibrium, i.e., molecules move back and forth between the two states at the same rate, so both phases remain present. If the temperature of a solid is measured carefully as the solid is heated, the temperature will be observed to rise until the melting point (m.p.) of the solid is reached, and then the temperature will remain almost constant while the solid melts. The heat absorbed during melting is the “heat of fusion,” the energy needed to move the molecules out of the crystal lattice of the solid. When the solid has completely melted, the addition of more heat again contributes to an increase in the temperature of the sample, now a liquid. This describes the melting of a pure solid. The melting point is characteristic of the compound, independent of source, purification procedure, etc., and is useful in identifying the compound. However, many different compounds have identical or very similar melting points. Eutectic diagram is a binary phase diagram shows the phases formed in differing mixtures of two elements over a range of temperatures. Eutectic point of mixture of two or more phases at a composition that has the lowest melting point, and where the phases simultaneously crystallize from molten solution at this temperature. Experimental procedure:
* We transferred a little of powdered of each 5 compounds [ pure Urea, pure Cinnamic Acid and 3 mixtures] into different Capillary Tubes. * We inserted Tubes into the melting point apparatus and set up the melting temperature for the heating apparatus as follows: * Pure substance with 125 C.
* 75%-25% with 100 C.
* 50%-50% with 90 C.
* The melting temperatures was determined...