Examples of Pure Substances

Examples of Pure Substances
Pure substances have a uniform chemical composition. Examples include water (liquid), diamond (solid), and oxygen (gas).

In chemistry, a pure substance is a material with a constant composition. In other words, it is homogeneous no matter when you sample it. A pure substance consists entirely of one type of atom or compound. It participates predictably in a chemical reaction.

Examples of Pure Substances

The best examples of pure substances are pure elements, molecules, and compounds:

The Gray Area

Some people consider any homogeneous mixture or alloy to be an example of a pure substance. This is the usual definition, but won’t get you the grade in a chemistry class. These examples of pure substances don’t consist of one type of atom or compound, but they do have a uniform structure. This type of pure substance needs to be free of contaminants or impurities:

  • Sterling silver (an alloy of silver and copper)
  • Honey
  • Air (a homogeneous mixture of gases)
  • Vegetable oil
  • Brass
  • Stainless steel
  • Tap water
  • Rubbing alcohol

Examples of Impure Substances

Some specimens are clear examples of impure substances:

  • Mixture of sand and salt
  • A bouquet of different flowers
  • Concrete
  • Clock
  • Automobile
  • A cake

How to Identify a Pure Substance

The only way to know for certain if a sample is a pure substance is to perform a chemical analysis. However, there are other clues that can help you make a determination:

  • Is is crystalline? Crystals are typically relatively pure compounds.
  • A pure substance is usually all one color. The exception is if the matter has unusual optical properties, such that it reflects or refracts light.
  • A pure substance has the same appearance and properties, no matter where you sample it.
  • If you magnify the matter, it should appear the same everywhere in its composition. The exception is when matter exists in multiple phases (e.g., melting ice).
  • If you can write the element symbol or chemical formula for a sample, it’s a pure substance.