Titration of 50.0mL of 0.130mol/L sulfurous acid with 0.14mol/L sodium hydroxide.
what species are responisble for the pH in the two equivalence points?
In the titration of sulfurous acid with sodium hydroxide, there are two equivalence points. The species responsible for the pH at each equivalence point can be determined by examining the reactions that occur.
1. The first equivalence point occurs when all the sulfurous acid (H2SO3) is completely neutralized by the sodium hydroxide (NaOH) to form sodium sulfite (Na2SO3) and water (H2O). The balanced equation for this reaction is:
H2SO3 + 2NaOH -> Na2SO3 + 2H2O
At this equivalence point, the pH is determined by the presence of sodium sulfite (Na2SO3), which is a salt that dissociates into sodium ions (Na+) and sulfite ions (SO3^2-) in water. Both sodium ions and sulfite ions are neutral species and do not significantly affect the pH. Therefore, the species responsible for the pH at the first equivalence point is water (H2O).
2. The second equivalence point occurs when all the sodium hydroxide (NaOH) is completely neutralized. In this case, sodium hydroxide reacts with the remaining sulfurous acid to form sodium bisulfite (NaHSO3) and water (H2O). The balanced equation for this reaction is:
H2SO3 + NaOH -> NaHSO3 + H2O
At this equivalence point, the pH is determined by the presence of sodium bisulfite (NaHSO3). Sodium bisulfite is also a salt that dissociates in water, forming sodium ions (Na+) and bisulfite ions (HSO3^-). Similar to the first equivalence point, both sodium ions and bisulfite ions are neutral species and do not significantly affect the pH. Therefore, the species responsible for the pH at the second equivalence point is water (H2O).