Titration: a Commonly Used Laboratory Technique

A titration is a commonly used laboratory technique where a solution of a known concentration (the titrant) is used to determine the concentration of another solution (analyte). We slowly add the known solution with a buret to the unknown solution until it reaches neutralization, indicating the equivalence point or the point at which chemically equivalent amounts of reactants have been mixed. Titrations are most commonly used when one needs to find the pH level of an unknown solution. In order to perform a titration, certain glassware must be utilized. We need to use volumetric glassware such as a volumetric flask, pipette, and burette and non-volumetric glassware such as a glass funnel, beaker, and conical flask.

Additionally, one must use an analytical balance to obtain accurate weighing of samples and precipitates. As mentioned before, the titrant (known solution) is added to the analyte (unknown solution) until the stoichiometric volume of the titrant reaches the equivalence point, or chemically equivalent quantities of bases and acids have been mixed. There are two methods that are commonly used to determine this equivalence point. One method is monitoring the pH during the titration with a pH electrode, a glass, ion-selective electrode that is sensitive to hydrogen ions, and the equivalence point identified at the point of rapid pH change. Another way to determine equivalence point is with an indicator which in this case is phenophtalein. The phenophtalein, the indicator in this specific experiment, will change color in response to chemical change implying that the endpoint has been reached. Phenolphthalein has a pH of 8.3-10, in which it will appear pink in basic solution and clear in acidic solutions. In order to carry out a successful titration, the concentration of the standard solution must be known very accurately. In this experiment, one needs to standardize the solution of sodium hydroxide (NaOH). It is possible to take the solid NaOH to prepare a solution but the mass may not be accurate due to sodium hydroxide’s hygroscopic characteristic, meaning it attracts water.

Therefore, the mass of the sodium hydroxide will include the mass of water along with CO2 from the air. Therefore, to determine the concentration of sodium hydroxide it needed to be titrated against a primary standard, which is potassium hydrogen phthalate in this experiment. A primary standard is a pure compound that will not decompose in room temperature and resist the absorption of water. KHP is dried before use and the exact mass of KHP can be determined using the analytic balance. Then, KHP is dissolved in water and then titrated with NaOH, creating the standard solution. This is necessary because standard solutions allow one to determine the concentration of other substances and perform the titration with accuracy. After making this standard solution of NaOH, the concentration of an unknown acid solution, the analyte, can be determined. Next, we determine the concentration of an aqueous solution of HCL by slowly titrating it with a solution of NaOH of known concentration until a faint pink color is reached and has persisted for about thirty seconds. The molarity of HCL is calculated based on the molarity and volume of the NaOH solution and volume of HCL solution.

By measuring the volume of NaOH added to HCL until it reaches neutralization and recording the concentration of NaOH in the titration, the number of moles of NaOH added to the flask can be calculated. At the end point, this is also the number of moles of HCL. The number of moles coupled with the volume of HCL solution can be used to calculate the molarity of HCL solution. Therefore, it is very important to record the volume of NaOH added to the HCl and the pH changes. Next, we determine the concentration of an aqueous solution of HCL by slowly titrating it with a solution of NaOH of known concentration until a faint pink color is reached and has persisted for about thirty seconds. The molarity of HCL is calculated based on the molarity and volume of the NaOH solution and volume of HCL solution. By measuring the volume of NaOH added to HCL until it reaches neutralization and recording the concentration of NaOH, the number of moles of NaOH added to the flask can be calculated. At the end point, this is also the number of moles of HCL. The number of moles coupled with the volume of HCL solution can be used to calculate the molarity of HCL solution.