These free B.Pharm notes on complexometric titrations cover chapter 12 of Pharmaceutical Inorganic and Analytical Chemistry (BP106T), a first-semester subject. Read the key points below, then study the complete chapter PDF. You can browse every chapter in the Pharmaceutical Inorganic and Analytical Chemistry category.
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Overview of complexometric titrations
These notes explain the principle of complexometric titration with EDTA, then the five types: direct, back, replacement, alkalimetric and indirect titrations. They describe metallochromic indicators, masking and demasking reagents, preparation and standardisation of 0.1 M disodium EDTA, and the assays of calcium gluconate and magnesium sulphate.
Key points on complexometric titrations
- In complexometric titration a metal ion binds a ligand to form a soluble, undissociated complex of fixed ratio.
- EDTA forms a stable 1:1 complex with most metal ions whatever their charge, while alkali metals form only weak complexes.
- With Eriochrome Black T as indicator, the colour changes from wine red to blue at the end point.
- A masking agent forms a stable soluble complex with an interfering ion, so only the target ion reacts with EDTA.
- Calcium gluconate is assayed by replacement titration, adding magnesium sulphate because direct titration of calcium gives no sharp end point.
Relevance to pharmacy practice
Complexometric titrations are used to assay metal-containing drugs such as calcium gluconate and magnesium sulphate and to analyse hard water. Masking and demasking let a pharmacist determine several metals in one sample without separating them, which makes the method valuable in quality control.
Every chapter in this subject builds on the one before it, so do not skip topics that look simple. Definitions, principles, procedures and examples are the parts that examiners return to most often, and a clear understanding here will also make later subjects easier to follow in the coming semesters.
Frequently asked questions on complexometric titrations
Why is the solution buffered in complexometric titration?
The reaction of the metal with EDTA releases H+ ions, and metallochromic indicators also change colour with pH. So the solution must be buffered to keep the pH constant.
How is 0.1 M disodium EDTA standardised?
It is standardised against calcium carbonate as primary standard. The solution is adjusted to pH 12-13 with sodium hydroxide, EBT is added, and it is titrated until purple changes to dark blue.
What is a replacement titration?
It is used when direct or back titration gives no sharp end point. The analyte metal displaces another metal from its EDTA complex, and the freed metal is titrated with standard EDTA.
Quick revision checklist
Use this self-test after reading the chapter on complexometric titrations. If you can do all of the following without looking at your notes, you are ready for the exam.
- I can explain: the principle of EDTA titrations
- I can explain: five types of complexometric titration
- I can explain: how metallochromic indicators work
- I can explain: masking and demasking reagents with examples
- I can explain: assays of calcium gluconate and magnesium sulphate
Study and exam tips
Start by reading the chapter once for the overall idea, then revise complexometric titrations using headings, definitions, principles, reactions and examples. Short-answer questions in the university exam usually ask for definitions, principles, procedures, reactions and uses, so write these in your own words and practise the equations, tables and flow charts that the chapter has.
For wider reading, standard books and open resources such as the NCBI Bookshelf help you confirm terms and see more examples. Revise complexometric titrations again a day later and again a week later, because spaced revision improves long-term memory.
This page is part of the Pharmaceutical Inorganic and Analytical Chemistry series for first-semester B.Pharm students on B.Pharm Guru, where every chapter has a short summary and a full PDF. Bookmark this page and share it with classmates who are preparing for the same exam.
Related notes: 14. GASTROINTESTINAL AGENTS, 15. RADIO PHARMACEUTICALS.
Next: 13. REDOX TITRATIONS. Back to the Pharmaceutical Inorganic and Analytical Chemistry category.
