AAT Bioquest

How do I know whether a substance is pure or impure?

Posted April 14, 2023


Studying the properties of the substance can indicate whether it is pure or impure. A pure substance will have these properties: 

  • Homogeneous with a uniform composition throughout its mass
  • Definite composition 
  • Definite physical and chemical properties
  • Sharp melting and boiling points

Elements and compounds are examples of pure substances. 

Impure substances will have these properties: 

  • Homogeneous or heterogeneous mixture with a variable composition throughout its mass
  • Made up of two or more pure substances mixed together in any ratio
  • Variable composition
  • Variable melting and boiling points

Solution of salt in water, air, seawater, and smog are common examples of impure substances.

Additional resources

Analytical advances in pharmaceutical impurity profiling

ReadiUse™ hydrogen peroxide solution *50 mM calibrated and stabilized solution*