What are the major species in a solution during the titration of citric acid with a strong base such as NaOH?
During the titration of citric acid (C6H8O7) with a strong base like sodium hydroxide (NaOH), several species are present. Let's understand the titration process and the major species involved.
1. Initially, before the addition of NaOH, the major species present in the solution are citric acid (C6H8O7) and water (H2O). As citric acid is a weak acid, it partially dissociates into hydrogen ions (H+) and citrate ions (C6H7O7^-).
C6H8O7 ⇌ H+ + C6H7O7^-
2. As NaOH is gradually added to the solution, it reacts with citric acid through a neutralization reaction, forming water and the corresponding sodium salt of citrate (NaC6H7O7).
H+ + NaOH → H2O + Na+
C6H7O7^- + Na+ → NaC6H7O7
3. Throughout the titration, the species present can be categorized into three major stages:
a. Before the equivalence point (H3Cit+ stage):
Prior to the equivalence point, excess citric acid is present. So, the major species in this stage are hydrogen ions (H+), citric acid (C6H8O7), citrate ions (C6H7O7^-), and water (H2O).
b. At the equivalence point (Cit3- stage):
At the equivalence point, all of the citric acid has reacted with the NaOH, resulting in the complete neutralization of the acid. Therefore, the major species during this stage are sodium ions (Na+), citrate ions (C6H7O7^-), and water (H2O).
c. After the equivalence point (Cit3- + Na+ stage):
Beyond the equivalence point, excess NaOH is present. Hence, the major species in this stage are sodium ions (Na+), citrate ions (C6H7O7^-), hydroxide ions (OH-), and water (H2O).
It is important to note that the exact concentration and ratio of the species present will depend on the volume and concentration of the NaOH solution added during the titration.