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Introduction to Chemical Mixtures

Author(s): David R. Caprette, PhD

Introduction to Chemical Mixtures

A biologist must be able to work with a variety of mixtures. He or she must be able to plan the preparation of mixtures, read formulas for mixtures, describe them, store them properly, dilute them, analyze them for content and/or concentration, pipette them, and handle them safely. This talk will present basic concepts and definitions, and the rationale behind descriptions of types of mixtures.  It is part of a presentation on the methodology related to understanding and preparing solutions.

Many, but not all, mixtures used in a biology laboratory are made by mixing a solid with water.  Many, but not all, of these mixtures are true solutions. Here are some examples of mixtures that a biologist might encounter in a laboratory. Some are true solutions and some are not.

  • physiological saline solutions
  • buffers
  • cell suspensions
  • soil suspensions
  • staining solutions
  • microbiological media
  • chromatography slurries
  • dishwater
  • milk
  • protein solutions
  • DNA solutions
  • density gradients

The word “mixture” can be defined as a heterogeneous association of substances that cannot be represented by a single chemical formula. This definition does not limit mixtures to solids mixed with liquids. Two or more gases, solids, or liquids can be mixed, and two or more different phases of matter can be combined in a mixture.  Because of the importance of liquid solutions and similar mixtures to biology, this series of talks will focus primarily on mixtures in which the major component is a liquid.