Conductometric titration is a method used to determine the endpoint of a titration by measuring the electrical conductivity of the solution. In the case of copper sulfate (CuSO₄) and sodium hydroxide (NaOH), the reaction involves the formation of copper hydroxide precipitate:
CuSO₄(aq) + 2NaOH(aq) → Cu(OH)₂(s) + Na₂SO₄(aq)
Here's how the conductometric titration works:
1. Initial Conductivity:
* The initial solution contains copper sulfate, which is a strong electrolyte, meaning it dissociates completely into ions (Cu²⁺ and SO₄²⁻) in solution. This high concentration of ions results in high electrical conductivity.
2. Adding Sodium Hydroxide:
* As NaOH is added dropwise, it reacts with Cu²⁺ ions, forming the insoluble copper hydroxide precipitate (Cu(OH)₂).
* The removal of Cu²⁺ ions from the solution decreases the conductivity.
* At the same time, Na⁺ and SO₄²⁻ ions are present in the solution, contributing to the conductivity.
3. Equivalence Point:
* At the equivalence point, all the Cu²⁺ ions have reacted with NaOH, forming the precipitate.
* The conductivity reaches a minimum because the solution primarily contains Na⁺ and SO₄²⁻ ions.
4. Post-Equivalence Point:
* After the equivalence point, excess NaOH is added.
* This further increases the conductivity due to the presence of free OH⁻ ions from NaOH.
Conductometric Titration Curve:
The conductivity changes during the titration can be plotted against the volume of NaOH added. This creates a graph with two linear segments:
* Segment 1: A decreasing slope as Cu²⁺ ions react with NaOH.
* Segment 2: An increasing slope after the equivalence point, due to the addition of excess NaOH.
The intersection of these two segments represents the equivalence point of the titration.
Advantages of Conductometric Titration:
* Suitable for colored or turbid solutions: Unlike visual titrations, it doesn't rely on color change for endpoint determination.
* Applicable for weak acids/bases: Conductometric titration can determine the equivalence point even for weak acids/bases, which don't show a sharp pH change.
* High accuracy: The method provides more accurate results compared to visual titrations.
Limitations:
* Requires specialized equipment (conductivity meter).
* The method can be affected by temperature changes.
In summary, conductometric titration is a valuable technique for determining the equivalence point of a reaction by measuring the conductivity changes in the solution. It's particularly useful for titrations involving colored or turbid solutions, weak acids/bases, and situations where visual endpoint determination is difficult.
