3.1:
Acid–Base Titration: Overview
Acid-base titration can be performed to determine an unknown concentration of acid using a known concentration of a base or vice versa.
When titrating an acid with a base, the titrant is gradually added to the acid, raising the pH. The pH change is plotted against the volume of the base to create a titration or pH curve.
The titration curves are S-shaped, though differences exist depending on whether the acid is strong or weak.
The pH at the start of the titration will be acidic but higher for a weak acid, assuming equal initial concentrations of acid.
The equivalence point is the point on the titration curve at which the moles of base equals the moles of acid in solution.
In the case of a strong acid, the equivalence point is reached when a strong base neutralizes all the hydronium ions produced by the strong acid; therefore, it always occurs at pH 7.
In contrast, a weak acid's equivalence point occurs at a pH greater than 7 and is reached when all the weak acid is converted into its conjugate base.
Near the equivalence point, there is a sudden jump in the pH of the solution. However, in a weak acid titration, this rapid pH shift is not as steep as in a strong acid titration.
3.1:
Acid–Base Titration: Overview
An acid-base titration is a technique used to determine the concentration of an unknown acid or base, using a titrant of known concentration–either a base for acid titration or an acid for base titration. The process involves gradually adding the titrant, leading to a predictable change in the pH of the solution. This change is plotted on a titration curve, showing how a solution's pH varies with the amount of titrant added. Such curves are instrumental in monitoring the titration's progress and identifying the endpoint.
Titration curves can be formed in various combinations: between strong acids and strong bases, strong acids and weak bases, or weak acids and strong bases. These curves typically display an S-shape, but their specific characteristics vary depending on the strength of the acid or base involved. For strong acids neutralized by strong bases, the equivalence point – where the moles of acid equal the moles of base – is reached at a pH of 7, indicating complete neutralization. In the case of weak acids, this equivalence point occurs above pH 7, reflecting the transformation of the weak acid into its conjugate base. The pH changes more significantly near the equivalence point in strong acid titrations compared to weak acid titrations. In the latter, there is also a buffer region and a half-equivalence point, at which the pH equals the pKa of the acid. The concentrations of the weak acid and its conjugate base are equal—on the other hand, titrating strong or weak bases with strong acid results in an inverted S-shaped curve, starting from a higher pH and decreasing with the addition of the strong acid.