What is the primary method for determining the concentration of an unknown solution?

The primary method for determining the concentration of an unknown solution is titration. Titration is a quantitative analytical technique used to determine the concentration of a solute in a solution by adding a titrant of known concentration until the reaction reaches completion, which is often indicated by a color change or a measurable electrical signal in the case of potentiometric titrations.

During a titration, the volume of titrant added is measured, allowing for the calculation of the unknown concentration using stoichiometry based on the balanced chemical reaction. This method is widely used because it provides precise and accurate measurements of concentrations and can be applied to a variety of solutions, including acids, bases, and redox reactions.

In contrast, the other options do not primarily serve the purpose of determining concentration. Evaporation might allow one to estimate concentration by removing solvent but is not a direct method. Filtration is typically used to separate solid particles from liquids, while recrystallization is a technique employed to purify solid compounds rather than measure concentration directly.