What is the concentration measurement of a hydrogen peroxide and water solution expressed in?

The concentration measurement of a hydrogen peroxide and water solution is expressed in terms of volume. This is because solutions are typically described using volume percentages, which indicate the amount of solute (in this case, hydrogen peroxide) in relation to the total volume of the solution. For example, a 20% hydrogen peroxide solution means that 20 parts of hydrogen peroxide are mixed with 80 parts of water to make a total of 100 volume parts of the solution. This volumetric approach is crucial in practical applications to ensure accurate mixing and predictable results in haircoloring processes.

While weight can also be a way to measure the concentration of a solution, it is less commonly used in haircoloring applications. Density and viscosity pertain more to the physical properties of the solution rather than its concentration, and are not the typical measurements used for expressing concentration in cosmetic formulations.