Criteria of Purity of a Substance
Criteria of Purity of a Substance
The melting point and boiling point of a substance indicates the purity of a substance. Every pure compound has a definite melting point or boiling point. If the substance melts at lower temperature or boils at a higher temperature then it is impure. The impurities depress the melting point and elevate the boiling point.
Melting Point: The pure solid substance melts sharply at a definite temperature while as impure substance will have a lower and indefinite melting point. In the laboratory it is generally determined in sulphuric acid as shown in figure.
melting point
Boiling Point: A liquid boils at a temperature at which its vapour pressure becomes equal to the atmospheric pressure. The presence of impurities raises the boiling point of the liquid. The apparatus which is generally-used for the determination of boiling point is shown in figure
boiling point
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