Study of Matter Compounds  Elmhurst College
Atoms Physical Properties Mixtures  Chemistry Department
Elements Chemical Properties    Virtual ChemBook

What are Mixtures and Solutions?

 A MIXTURE is a combination of two or more substances that are not chemically united and do not exist in fixed proportions to each other. Most natural substances are mixtures.

In the graphic on the left there are four substances - water, alcohol, oil, and food color dye.

 MIXTURES

 PURE COMPOUNDS
 A mixture can be physically separated into pure compounds or elements.  A pure compound has a constant composition with fixed ratios of elements.
 Just about everything that you can think of is probably a mixture. Even the purest of materials still contain other compounds as impurities. Although it is almost physically impossible to isolate absolutely pure substances, a substance is said to be pure if no impurities can be detected using the best available analytical techniques.

 Mixtures may exhibit a changing set of physical properties.

For example, mixture of alcohol and water boils over a range of temperatures.

Physical properties such as boiling point or melting point of pure substances are invariant.

For example, pure water boils at 100 degrees C

 HOMOGENEOUS MIXTURES

HETEROGENEOUS MIXTURES
 The prefixes "homo"- indicate sameness The prefixes: "hetero"- indicate difference.
A homogeneous mixture has the same uniform appearance and composition throughout. Many homogeneous mixtures are commonly referred to as solutions.

A heterogeneous mixture consists of visibly different substances or phases. The three phases or states of matter are gas, liquid, and solid.

Graphic on the left of "Dancing Raisins" shows liquid, solid, and gas substances in a heterogeneous mixture.

Particle size distinguishes homogeneous solutions from other heterogeneous mixtures. Solutions have particles which are the size of atoms or molecules - too small to be seen.

A colloid is a homogeneous solution with intermediate particle size between a solution and a suspension. Colloid particles may be seen in a beam of light such as dust in air in a "shaft" of sunlight. Milk, fog, and jello are examples of colloids.

In contrast a suspension is a heterogeneous mixture of larger particles. These particles are visible and will settle out on standing. Examples of suspensions are: fine sand or silt in water or tomato juice.
Corn oil is homogeneous, White vinegar is homogeneous. A sugar solution is homogeneous since only a colorless liquid is observed. Air with no clouds is homogeneous. For example beach sand is heterogeneous since you can see different colored particles. Vinegar and oil salad dressing is heterogeneous since two liquid layers are present, as well as solids. Air with clouds is heterogeneous, as the clouds contain tiny droplets of liquid water.

 

SOLUTIONS are homogeneous mixtures.

A solution is a mixture of two or more substances in a single phase. At least two substances must be mixed in order to have a solution. The substance in the smallest amount and the one that dissolves or disperses is called the SOLUTE. The substance in the larger amount is called the SOLVENT. In most common instances water is the solvent. The gases, liquids, or solids dissolved in water are the solutes.

In the graphic, the blue bottle is a homogeneous solution mixture of water, KOH, glucose, oxygen gas dissolved, and methylene blue - an indicator.

 Since solutions are mixtures, their compositions may vary over a very wide range. The concentrations may be expressed using a variety of measures. The non-specific terms concentrated and dilute are sometimes used. A concentrated solution has a relatively large (but non-specific) amount of solute dissolved in a solvent. A dilute solution has a smaller quantity of solute dissolved.

 TYPES OF SOLUTIONS

 Concentrations
 

Solute
Less than 50%

Solvent
More than 50%

 Examples

 liquid

 liquid

 alcohol - water
wine beer, vodka
acetic acid / water - vinegar

 solid

liquid

 salt - water
saline (NaCl) solution
sugar solution
CaCO3 - hard water

 gas

liquid

 oxygen - water
 CO2 - carbonated water
NH3 - ammonia solution

 gas

 gas

air =
oxygen - nitrogen
 

 gas

 solid
 hydrogen - platinum  

 liquid

gas

 water in air
 

 solid

gas

smog
 

liquid

solid

 mercury - another metal
 

 solid

solid

 alloy