The titration of acids and bases is an experimental technique used to determine the amount of an acid or base in a solution, i.e. the concentration of the solution. By definition, a titration is an analytical procedure for the quantitative analysis of a substance by means of detecting an essentially complete reaction in solution with a reagent of known concentration.
To perform a titration, a buret (a volumetric cylinder calibrated in divisions of 0.1 mL) is used to deliver an accurate volume of solution. The buret is filled with base of a known concentration, and is placed above a beaker or flask containing an acidic solution for which the concentration will be determined. This type of titration is referred to as 'titrating an acid with a base'; the opposite is also common. The acidic solution contains an indicator, a dye that changes color as a function of pH when the reaction reaches completion.
The base is slowly added to the acidic solution. When the number of moles of OH- added is exactly equivalent to the number of moles of H+ supplied from the acid, the reaction has reached its equivalence point. Laboratory scientists, however, do not actually observe the equivalence point; instead, they determine the concentration of the solution at the reaction's end point, which is accompanied by the dye's color change. Stating the titration has reached its 'equivalence point' when we note a solution's color change is incorrect. Although there is error associated with the discrepancy, indicators are chosen so the error is typically minimal.
This module simulates the useful laboratory technique of titration using both an indicator and a pH meter to determine the end point. In this acid-base titration, NaOH is added from a buret to a container of one of three acids: HCl, HOAc, or HClO. Three indicators are available: Methyl Orange, Phenolphthalein, and Thymolphthalein, each of which can potentially mark the equivalence point by changing color.
INSTRUCTIONS
1. Select an acid to add to the beaker by clicking on one of the three
Acid option buttons. In all experiments, exactly 25. mL of acid
solution are used.
2. Designate the amount of acid by adjusting the scroll bar. The name
above the scroll bar indicates the acid selected. The scroll bar
adjusts the concentration between 0.10 and 1.00 M.
3. Designate the concentration of base from 0.10 to 1.00 M by
adjusting the NaOH scroll bar.
4. Select an indicator by clicking on one of the three Indicator options.
5. To titrate, click on one of the three Add Base buttons. Each button
adds base aliquots of different volumes; use any combination of
buttons to add the desired amount of base.
When performing an acid-base titration with an indicator, it is important to work slowly and carefully. The point at which the acid solution with indicator just begins to change color is the equivalence point. In this program, as in the laboratory, if you add too much base too quickly and pass the end point, accuracy is lost. The experiment, therefore, becomes invalid and must be repeated to obtain a more accurate measurement.
