Potentiometeric Titrations

Title: Potentiometric titration Objective: The purpose of this experiment was to create a titration curve by titration of formic acid by potentiometric titration with standard sodium hydroxide (NaOH) and pH meter. Once you have collected data for the remaining categories, compare and compare the equivalence points to see how concentration of each acid affects acid weakness and strength. Method: 0.020 M formic acid (HCCOOH) was obtained. Calibrate the pH meter using the pH meter calibration instructions in the appendix.

Figure 3. This figure shows a titration curve of 25.00 mL of 0.100 CHCOH (weak acid) titrated with 0.100 NaOH (strong base) and a titration curve of HCl (strong acid) titrated with NaOH (strong base). The pH range of the color change of phenolphthalein, litmus and methyl orange is indicated by the shaded area. Cladonia is a good indicator for HCl titration because its color change includes equivalence. However, when adding about 12 mL of NaOH, pH will be within the color gamut of litmus and will not deviate from the range until 25 mL is added, so do not use Litmus for CHCOH titration. The change in color is very slow and occurs during the addition of 13 mL NaOH, so litmus is invalid as an index of equivalence.

In many titration reactions, you can find an appropriate visual color indicator that signals the endpoint at a point that is very close to the equivalence point or signal point. Such titrations classified according to the nature of the chemical reaction taking place between the sample and the titrant include acid-base titration, precipitation titration, complex formation titration, and redox titration. In acid-base titration (ie titration of acid with base or vice versa) the indicator can exist in two forms, acid form and base form, they are substances of different color. For example, litmus is blue in alkaline solution and red in acidic solution. Phenolphthalein is colorless in acidic solution and red in alkaline solution. You can choose from various acid-base indicators not only from two kinds of colors but also from the viewpoint of sensitivity to acids and bases.

Acid-base titration is an experimental method for determining unknown concentrations by accurately neutralizing acids or bases with known concentrations of acids or bases. This makes it possible to quantify the concentration of unknown solution. Acid-base titration can also be used to quantify the purity of chemical substances. Before starting the titration, it is necessary to select a suitable pH indicator, preferably a color change near the reaction point (referred to as the "end point"); this is the point at which the product reacts with an equal amount of reactants . This is some common equivalence index.