Complexometric titration is a type of titration in which the formation of a complex between a metal ion and a ligand is used to determine the concentration of metal ions in a solution. It is widely used in analytical chemistry, especially for water hardness and metal analysis.
Basic Idea
- A ligand is a molecule that can bind to a metal ion to form a stable complex.
- In complexometric titration, the titrant is a ligand (like EDTA) that reacts with the metal ions in solution.
- The endpoint is detected when all metal ions have reacted to form complexes.
How It Works
- Setup:
- A solution containing metal ions (like Ca²⁺, Mg²⁺) is placed in a flask.
- EDTA solution (ligand) is added from a burette as the titrant.
- A metal ion indicator (like Eriochrome Black T) is added, which changes color when all metal ions are bound.
- Titration Process:
- EDTA binds with the metal ions to form a colorless complex:
Metal²⁺ + EDTA → [Metal–EDTA]²⁻ - The indicator changes color at the endpoint, signaling that all metal ions are complexed.
- EDTA binds with the metal ions to form a colorless complex:
- Calculation:
- The volume of EDTA used and its concentration allows calculation of the metal ion concentration in the solution.
Applications
- Water analysis: Measuring hardness (Ca²⁺ and Mg²⁺).
- Pharmaceuticals: Determining metal content in drugs.
- Food and beverages: Detecting metal ions like calcium or magnesium.
- Industrial processes: Quality control of metals and alloys.
Advantages
- Highly specific for metal ions.
- Can be used for mixtures of metals with proper masking agents.
- Accurate and reliable.
Example
- Determining calcium hardness in water:
- Titrate Ca²⁺ ions with EDTA.
- Indicator: Eriochrome Black T (red → blue at endpoint).