Volume Percent Concentration (v/v%)

Volume Percent Concentration Example

Volumetric flasks are used to accurately prepare volume percent solutions.
Volumetric flasks are used to accurately prepare volume percent solutions. Science Photo Library Ltd / Getty Images

Volume percent or volume/volume percent (v/v%) is used when preparing solutions of liquids. It is very easy to prepare a chemical solution using volume percent, but if you misunderstand the definition of this unit of concentration, you'll experience problems.

Percent Volume Definition

Volume percent is defined as:

v/v % = [(volume of solute)/(volume of solution)] x 100%

Note that volume percent is relative to volume of solution, not volume of solvent.

For example, wine is about 12% v/v ethanol. This means there are 12 ml ethanol for every 100 ml of wine. It is important to realize liquid and gas volumes are not necessarily additive. If you mix 12 ml of ethanol and 100 ml of wine, you will get less than 112 ml of solution.

As another example, 70% v/v rubbing alcohol may be prepared by taking 700 ml of isopropyl alcohol and adding sufficient water to obtain 1000 ml of solution (which will not be 300 ml). Solutions made to a specific volume percent concentration typically are prepared using a volumetric flask.

When Is Volume Percent Used?

Volume percent (vol/vol% or v/v%) should be used whenever a solution is prepared by mixing pure liquid solutions. In particular, it's useful where miscibility comes into play, as with volume and alcohol.

Acid and base aqueous reagents are usually described using weight percent (w/w%). An example is concentrated hydrochloric acid, which is 37% HCl w/w.

Dilute solutions are often described using weight/volume % (w/v%). An example is 1% sodium dodecyl sulfate.  Although it's a good idea to always cite the units used in percentages, it seems common for people to omit them for w/v%. Also, note "weight" is really mass.