Calculate pH at different stages of acid-base titration for strong and weak acids/bases. Determine equivalence point, buffer regions, and concentration unknowns.
pH
--
pOH
--
[H⁺] Concentration
--
[OH⁻] Concentration
--
Equivalence Volume
--
Titration Region
--
Titration is a quantitative analytical technique used to determine the concentration of an unknown solution by reacting it with a solution of known concentration (titrant) until the equivalence point is reached, indicated by a color change or pH measurement.
The equivalence point is the stage in a titration where the moles of acid equal the moles of base (nH⁺ = nOH⁻). At this point, all the analyte has been neutralized by the titrant, and the pH depends on the nature of the salt formed.
The pH calculation depends on the titration region: before equivalence (excess analyte), at equivalence (hydrolysis of salt), or after equivalence (excess titrant). For weak acid/base systems, the Henderson-Hasselbalch equation is used in buffer regions.
Strong acid-strong base titrations have a sharp equivalence point at pH 7. Weak acid-strong base titrations have equivalence points above pH 7, while weak base-strong acid titrations have equivalence points below pH 7.
The Henderson-Hasselbalch equation (pH = pKa + log([A⁻]/[HA])) is used in buffer regions of weak acid-strong base titrations, where both the weak acid and its conjugate base are present in significant amounts.
Use the formula nH⁺·Ma·Va = nOH⁻·Mb·Vb, where n is the number of H⁺ or OH⁻ ions, M is molarity, and V is volume. Knowing the titrant concentration and volume at equivalence point allows calculation of the unknown concentration.
At the equivalence point, all weak acid is converted to its conjugate base, which undergoes hydrolysis to produce OH⁻ ions, making the solution basic (pH > 7). The pH can be calculated using [OH⁻] ≈ √(Kb·C), where Kb = Kw/Ka.