How to Determine the Melting Point of a Substance

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The melting point is the temperature at which a solid changes into a liquid by adding heat. It is the same as a substance’s freezing point, but it is specified at standard atmospheric pressure rather than at zero bar.

Melting is a chemical process that occurs at the molecular level in crystalline substances such as metals, ceramics and glass. The process requires the movement of hydrogen atoms within the crystal lattice. This reorganizes the structure of the material to produce an ordered, symmetrical melt that can be separated from the solid by cooling. The melting point of a substance is an important measurement that can be used to determine its purity. A pure substance has a higher melting point and a narrower melting range than a mixture.

Usually, the melting point of a compound is determined by observing the behavior of a small sample of the material in an oil bath. It is heated until it begins to melt, and then the melting rate is monitored at regular intervals with a magnifier. The rate at which the melt is formed can then be correlated to the temperature of the melting point.

An alternative method is to use a capillary tube to measure the melting point of a sample. A small amount of naphthalene is placed in a capillary tube that is sealed at one end, and the tube is slowly heated. The temperature at which the naphthalene starts to melt is taken, and the melting point of the naphthalene is calculated from the slope of the curve obtained.