Titration is an analytical technique that allows you to determine the concentration of a substance based on its chemical reaction with another substance, called the titrant. You slowly add a standard solution of the titrant to the solution with the unknown concentration. Often you can tell the reaction is complete using a chemical indicator that changes color at the reaction endpoint. You measure the volume of the standard solution that you used for titration, and from there you can calculate the concentration of the other substance. As an example, the concentration of 10 ml of hydrochloric acid (HCl) solution can be calculated using a 0.15 molar standard solution of sodium hydroxide (NaOH).
Write down the equation of the chemical reaction that the titration is based on. In the example, it is HCl + NaOH = NaCl + H2O.
Multiply the volume (in L) of the standard solution by its concentration (in moles/L) to determine the number of moles of the titrant used for titration. For example, suppose the volume of the NaOH solution used to reach the endpoint was 22.4 ml or 0.0224 L. Hence, the number of moles of NaOH equals 0.0224 L x 0.15 moles/L, or 0.00336 moles.
Use this figure to determine the number of moles of the unknown compound using the equation of its chemical reaction. In the example, it's very simple to calculate, because the equation shows that 1 mole of HCl reacts with 1 mole of NaOH. Thus, if you used 0.00336 moles of NaOH to neutralize the HCl, you began with 0.00336 moles of HCl.
Divide this figure -- the number of moles you just calculated -- by the aliquot volume (in L) to calculate the unknown concentration. In our example, the aliquot of HCl was 10 ml or 0.01 L. Hence, the concentration of HCl would be 0.00336 moles/0.01L = 0.336 mole/L = 0.336 M.