Examples of Pure Substances 1

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:

  • Hydrogen gas
  • Gold metal
  • Sugar (sucrose)
  • Baking soda (sodium bicarbonate)
  • Ammonia
  • Diamond
  • Copper wire
  • Silicon chip
  • Copper sulfate
  • Ethanol (pure grain alcohol)

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.

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One thought on “Examples of Pure Substances

  • Shaun Chen

    There are many other examples where daily used language or understanding contradicts with the definitions or understanding in science. When a layman of science says “the honey is pure” or “the air is pure”, it has very different meaning from science. A pure substance contain only one type of substance (an element or a compound). A pure substance hence has a fixed melting and boiling. Hence, honey and air is never pure from the scientific point of view.

    One should not mix up the meaning of “pure” in science with daily used language. This is one of the key challenges in teaching and learning of science for a teacher like me.