What is a substance?

Substances can often be mistaken with mixtures, when in fact they are two very separate concepts when it comes to chemistry and hazardous chemicals. The following is a basic comparison of both substances and mixtures:

Chemical Substances

  • A chemical substance is defined as a form of matter that has a constant chemical composition and can be distinguished by unique properties.
  • Chemical substances can be solids, liquids, gases, or plasma.
  • Pure chemical compounds are substances composed of bonded molecules or ions. For example, pure water is s chemical substance since it always has the same ratio of hydrogen to oxygen. However, seawater is a mixture since it contains sand, salt, and other complex molecules.

Chemical Mixtures 

  • A mixture is made of two or more chemical substances that are physically combined, yet not chemically bonded.
  • Mixtures can be alloys, solutions, suspensions, and colloids.
  • Heterogenous mixtures are composed of more than one chemical substance and can be visually distinguished from one another. Trail mix is a great example of a heterogenous mixture as it is made up of a visually distinguished set of substances—AKA the person eating this snack can pick out the raisins.
  • Homogenous mixtures are physically combined but cannot be visually distinguished. Powdered lemonade mix can be used as an example. By pouring the lemonade powder into water the lemonade flavoring and sugar dissolves into an indistinguishable refreshing yellow drink. However, when mixed there was no chemical bond made.

There are thousands upon thousands of substances that are recognized by the Chemical Abstracts Service. All existing chemical substances are identified by a long string of numbers referred to as CAS identification. This identifying number is essential for workplace safety when it comes to GHS labels, SDS sheets.


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