To determine the concentration of an unknown solution, you can use a method known as titration.

Titration is a widely used laboratory technique for quantitative chemical analysis that allows you to ascertain the concentration of an unknown solution. The process involves the gradual addition of a solution with a known concentration, called the titrant, to the unknown solution, referred to as the analyte. The titration continues until the reaction between the two solutions is complete, which is marked by the equivalence point or endpoint.

Before starting the titration, it is essential to know the concentration of the titrant and the volume of the analyte. Additionally, you will require an indicator— a substance that changes color when the reaction reaches completion. One of the most commonly used indicators is phenolphthalein, which appears colorless in acidic solutions and turns pink in basic solutions.

The titration procedure begins by adding the analyte to a flask along with several drops of the indicator. The titrant is then added slowly from a burette, a piece of laboratory equipment designed for the precise measurement of liquid volumes. As the titrant is added, it reacts with the analyte, causing the solution in the flask to change color gradually.

When you observe a color change, it indicates that the analyte has fully reacted with the titrant, signaling that the reaction is complete. At this moment, you should record the volume of titrant dispensed from the burette.

To calculate the concentration of the unknown solution, you can use the following formula:

The amount of substance, $n$, can be determined using the stoichiometry of the reaction, which is based on the ratio of reactants and products as defined by the balanced chemical equation, along with the known concentration and volume of the titrant.

It is crucial to perform the titration process with care and precision to ensure that your results are reliable and accurate.