Advanced Topic 937 of 1102 Analytical, Lab & Spectroscopy
Complexometric Titration
Uses EDTA to determine metal ions such as calcium and magnesium.
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In-depth explanation of Complexometric Titration
Complexometric titrations use a ligand that forms a stable complex with metal ions, most commonly the aminopolycarboxylate EDTA, which binds most metal ions in a 1:1 ratio. The metal concentration is determined by titrating with a standard EDTA solution, and the endpoint is detected by a metallochromic indicator such as Eriochrome Black T, whose colour changes when the free metal ion is used up. The pH must be controlled with a buffer, because EDTA is a weak acid whose binding strength depends on pH. Masking agents suppress interference from other metal ions. The method is widely used for determining water hardness and metals in pharmaceuticals.
Going deeper: Complexometric Titration
Key ideas: EDTA (H4Y) forms 1:1 complexes, so moles of EDTA equal moles of metal. Formation constants are large (log K near 10.7 for Ca2+ and 8.7 for Mg2+ at the right pH) and depend on pH, with buffer pH 10 (NH3/NH4Cl) typical for hardness. Eriochrome Black T goes from wine red (metal bound) to blue (free) at endpoint. Report hardness as mg CaCO3 per litre.
Common mistakes and connections: Students forget to buffer, so the colour change is poor and the complex does not form fully. Indicator blocking occurs when interfering metals such as Cu or Fe bind indicator irreversibly. Using the 2:1 ratio by mistake is common, since EDTA binds one metal per molecule. Slow dissolution of EDTA disodium salt matters when making the standard. Related to coordination chemistry, chelation and equilibrium constants.
Visualization of Complexometric Titration
Titrating 25 mL of 0.01 M Ca2+ with 0.01 M EDTA at pH 10, pCa jumps at 25 mL, the sharp change that Eriochrome Black T signals by colour. The interactive lesson shows this as a live animation or chart.
Worked example and use case
Total water hardness, as calcium and magnesium, is determined by titration with EDTA at pH 10 using Eriochrome Black T.
Frequently asked questions about Complexometric Titration
What is Complexometric Titration?
Uses EDTA to determine metal ions such as calcium and magnesium.
Is Complexometric Titration a beginner, intermediate or advanced topic?
Complexometric Titration is a advanced topic in Analytical, Lab & Spectroscopy. It builds on beginner and intermediate topics, so review those first if needed.
What should I learn before Complexometric Titration?
Study these earlier topics in Analytical, Lab & Spectroscopy first: Titrimetric Analysis, Back Titration, Redox Titrations.
What comes after Complexometric Titration?
The next topics in Analytical, Lab & Spectroscopy are Potentiometric Titration and Conductometric Titration.
Can I practise Complexometric Titration with quizzes?
Yes. The interactive lesson includes a self-check question on Complexometric Titration, and the Analytical, Lab & Spectroscopy quiz draws on every topic in this area.
Where Complexometric Titration fits in Analytical, Lab & Spectroscopy
Complexometric Titration is topic 61 of 99 in Analytical, Lab & Spectroscopy.