Dilution ratio

For the economics concept, see Concentration ratio.

In chemistry and biology, the dilution ratio or factor is the total number of unit volumes in which the material is dissolved. It is often used for simple dilutions, one in which a unit volume of a liquid material of interest is combined with an appropriate volume of a solvent liquid to achieve the desired concentration. The diluted material must be thoroughly mixed to achieve the true dilution. For example, a 1:5 dilution (verbalize as "1 to 5" dilution) entails combining 1 unit volume of solute (the material to be diluted) with (approximately) 4 unit volumes of the solvent to give 5 units of total volume. Note that some solutions and mixtures take up slightly less volume than their components.

The dilution factor is frequently expressed using exponents: 1:5 would be 5e−1 (5⁻¹ i.e. one-fifth:one); 1:100 would be 10e−2 (10⁻² i.e. one hundredth:one), and so on.

There is often confusion between dilution ratio (1:n meaning 1 part solute to n-1 parts solvent) and dilution factor (1:n+1) where the second number (n+1) represents the total volume of solute + solvent. In scientific and serial dilutions, the given ratio (or factor) often means the ratio to the final volume, not to just the solvent. The factors then can easily be multiplied to give an overall dilution factor as follows (for the 1 part of solute to n parts solvent example above):

$\mbox{dilution factor} = \frac{\mbox{final volume}}{\mbox{initial volume}} = \frac{\mbox{n+1}}{\mbox{1}}$

In other areas of science such as pharmacy, and in non-scientific usage, a dilution is normally given as a plain ratio of solvent to solute.

See also

• Fraction (chemistry)
• Concentration