Conductometric titration is a technique in which the electrical conductivity of a solution is measured during titration. The conductivity depends on the concentration and mobility of the ions present in the solution. As titration progresses, the ions are replaced, and the conductivity changes accordingly, which is plotted on a titration curve. Different types of titrations (acid-base, precipitation, complexometric) give distinct curves.


Types of Conductometric Titration Curves:

  1. Strong Acid with a Strong Base
    Example: Hydrochloric acid (HCl) vs. sodium hydroxide (NaOH)

    • Initial Conductivity: HCl is a strong acid, and its ions (H⁺ and Cl⁻) have high conductivity. Hence, the initial conductivity is high.
    • During Titration: When NaOH is added, OH⁻ ions neutralize H⁺ ions to form water, which has low conductivity. As H⁺ ions are removed, the conductivity decreases.
    • End Point: At the equivalence point, all H⁺ ions are neutralized, and Na⁺ and Cl⁻ ions remain. The conductivity rises again after the equivalence point due to the excess OH⁻ ions added from NaOH, which are more mobile.
    • Shape of the Curve: A V-shaped curve, where the conductivity decreases initially and then increases after the equivalence point.

  2. Weak Acid with a Strong Base
    Example: Acetic acid (CH₃COOH) vs. NaOH

    • Initial Conductivity: Acetic acid is a weak acid, so it is only partially dissociated, and its initial conductivity is low.
    • During Titration: As NaOH is added, OH⁻ ions neutralize H⁺ ions, but since acetic acid dissociates weakly, the conductivity decreases slowly.
    • End Point: At the equivalence point, the solution contains sodium acetate (CH₃COONa), which dissociates completely but contributes less to conductivity than free ions like H⁺. After the equivalence point, excess OH⁻ ions from NaOH increase conductivity.
    • Shape of the Curve: The curve shows a gradual decrease in conductivity, followed by a sharp rise after the equivalence point.

  3. Strong Acid with Weak Base
    Example: HCl vs. Ammonium hydroxide (NH₄OH)

    • Initial Conductivity: HCl fully dissociates, so the initial conductivity is high.
    • During Titration: As NH₄OH is added, NH₄⁺ and Cl⁻ form, but NH₄OH is a weak base and dissociates less, so the decrease in conductivity is less pronounced.
    • End Point: At the equivalence point, the solution contains ammonium chloride (NH₄Cl), which dissociates into NH₄⁺ and Cl⁻. There is a less drastic change in conductivity as NH₄⁺ is less mobile than H⁺. Beyond the equivalence point, conductivity increases slowly due to the excess NH₄OH.
    • Shape of the Curve: A slight V-shaped curve with a less pronounced rise after the equivalence point.

  4. Precipitation Titration
    Example: Silver nitrate (AgNO₃) vs. Sodium chloride (NaCl)

    • Initial Conductivity: Both NaCl and AgNO₃ are strong electrolytes and fully dissociate in water. Hence, the initial conductivity is high.
    • During Titration: As AgNO₃ is added, Ag⁺ reacts with Cl⁻ to form a precipitate (AgCl), which removes conductive ions from the solution, causing the conductivity to drop.
    • End Point: At the equivalence point, all Cl⁻ ions are precipitated as AgCl, and the conductivity reaches a minimum. After the equivalence point, the addition of excess AgNO₃ introduces more NO₃⁻ and Ag⁺, increasing conductivity.
    • Shape of the Curve: The curve shows a sharp decrease in conductivity, followed by a rise after the equivalence point.

  5. Complexometric Titration
    Example: EDTA vs. Metal ion (e.g., Ca²⁺)

    • Initial Conductivity: The solution contains free metal ions like Ca²⁺, which contribute to conductivity.
    • During Titration: As EDTA is added, it forms a complex with the metal ions, reducing the number of free ions in the solution, and causing the conductivity to decrease.
    • End Point: At the equivalence point, all metal ions have formed complexes with EDTA, and the conductivity stabilizes. Further addition of EDTA, a weak electrolyte, does not significantly increase conductivity.
    • Shape of the Curve: A gradual decrease in conductivity followed by a plateau after the equivalence point.

Key Takeaways from Conductometric Titration Curves:

  • The shape of the curve depends on the type of titration.
  • Strong electrolytes tend to have sharp changes in conductivity, while weak electrolytes exhibit more gradual changes.
  • The equivalence point is identified where the curve either changes direction or stabilizes, depending on the titration type.