Defining a Titration Curve
A titration curve is a graphical plot illustrating the change in pH (or other measurable property) of a solution as a titrant (a solution of known concentration) is gradually added to a sample solution. Typically, the pH is plotted on the y-axis, and the volume of titrant added is plotted on the x-axis, providing a visual representation of the reaction's progress.
Key Components and Features
A typical titration curve features a relatively flat region at the beginning (before significant reaction occurs), followed by a sharp, vertical rise or fall in pH, indicating the equivalence point. This point is where the moles of titrant precisely neutralize the moles of the analyte. For weak acid/base titrations, a buffer region also appears before the equivalence point, where the solution resists significant pH changes.
Examples: Strong vs. Weak Acid-Base Titrations
In a strong acid-strong base titration, the curve shows a very steep and symmetrical pH change around the equivalence point, which occurs at pH 7. Conversely, weak acid-strong base titrations exhibit a less steep pH change, a distinct buffer region, and an equivalence point at a pH greater than 7 due to the conjugate base hydrolysis. Similarly, weak base-strong acid titrations have an equivalence point at a pH less than 7.
Importance and Applications
Titration curves are crucial for determining the unknown concentration of an analyte (using the equivalence point), identifying the strength of an acid or base, and calculating the acid dissociation constant (pKa) or base dissociation constant (pKb) from the half-equivalence point. They also help in selecting the appropriate pH indicator for a specific titration, ensuring its color change aligns with the equivalence point.