Friday, 23 January 2015

Melting Point

Melting Point

The melting point is the amount of heat at which a solid changes into the liquid at atmospheric pressure. During change of state of a pure substance, the temperature remains constant since all the heat is used in the fusion process. Thus the melting point of pure substances defined and reproducible, and it can be used to identify a product, if it has been previously reported.

The presence of impurities has considerable influence on the melting point. According to Raoult's law all solute produces a freezing-point depression, or a decrease in the melting temperature. Act solute impurities and decrease the melting point of the main substance solvent. If there is a significant amount of impurity, the mixture may have a wide range of temperatures in which melting point is observed.
Thus it is noted that:

a) The pure solids have a stable melting point and melted in a small temperature range.

b) The presence of impure metal lowers the melting point and causes the sample based on a wide temperature range.

c) The presence of moisture or solvent gives incorrect fusion points.