Mixtures

Pure substances are uniform throughout with a definite composition and properties, while mixtures are physical combinations of two or more pure substances. The properties of the substances in a mixture retain their own properties.

We can further divide pure substance in chemistry into elements and compounds.  An element is basically the name of a type of atom defined by the number of protons in the nucleus.  A compound in a chemical combination of two or more elements.  A compound is the name of a type of molecule (chemically bonded atoms).

Note:  Physical combination means that substances are just dispersed or close together. A chemical combination means that the atoms are chemical attached creating new molecules with new properties.  Chemical bonds cannot be separated by physical means.

Mixtures can be divided into homogeneous mixtures that appear to be a single substance and heterogeneous mixtures that are obviously two or more substances.

All mixtures are composed of a solute and a solvent. The solute is the substance that is dissolved or dispersed, while the solvent is the substance that does the dissolving.  The solvent separates and keeps the solute particles apart.

Mixture can be divided into three categories:

Solutions are homogeneous and clear.  The particles are so small they cannot be seen and do not reflect light.

     Ex:  windex, tap water, air

Colloids are homogeneous but appear cloudy.  Some of the particles are large enough to reflect light even though they can’t be seen with the naked eye.

     Ex:  milk, fog, mayonnaise

Suspensions are heterogeneous.  Given time gravity will separate a suspension with the most dense particles on the bottom, and the least dense (lightest) particles rising to the top.

     Ex:  Italian salad dressing, oil and water