using boiling point and melting point as criteria for purity of a chemical substance?

Duche

3 months ago

Using Melting Point and Boiling Point as Criteria for Purity of a Chemical Substance
1. Melting Point
The melting point of a substance is the temperature at which a solid changes into a liquid.
A pure substance melts at a fixed and sharp temperature.
An impure substance melts over a range of temperatures and usually at a lower temperature than the pure substance.
Example:
Pure ice melts exactly at 0°C at standard pressure.
Conclusion:
If a substance melts at the known melting point and within a narrow range, it is likely pure.
2. Boiling Point
The boiling point is the temperature at which a liquid changes into gas.
A pure liquid boils at a constant temperature.
An impure liquid boils over a range of temperatures and usually at a higher temperature than the pure substance.
Example:
Pure water boils at 100°C at standard atmospheric pressure.
Conclusion:
If a liquid boils at the exact known boiling point, it is likely pure.
Summary
Melting point and boiling point are used to test purity because:
Pure substances have sharp, constant melting and boiling points.
Impurities change these temperatures and cause a temperature range instead of a fixed point.