Introduction to Precipitation, Complexometric & Gravimetry
Unit 3 covers a diverse range of analytical techniques. Precipitation titrations are key for halide estimation (Cl-, Br-). Complexometric titrations using EDTA are the gold standard for metal ion analysis (Calcium, Magnesium). Gravimetry teaches you the most precise method of analysis based on mass measurement. Diazotisation introduces you to organic functional group analysis.
Syllabus & Topics
- 1Precipitation Titrations: Mohr’s method, Volhard’s, Modified Volhard’s, Fajans method
- 2Estimation of Sodium Chloride (NaCl)
- 3Complexometric Titration: Classification, Metal ion indicators (Eriochrome Black T)
- 4Masking and Demasking agents
- 5Estimation of Magnesium Sulphate & Calcium Gluconate
- 6Gravimetry: Principle, Steps, Co-precipitation & Post-precipitation
- 7Estimation of Barium Sulphate
- 8Diazotisation Titration: Principle & Application (Sodium Nitrite)
Learning Objectives
Frequently Asked Questions (FAQs)
Q1. What is the difference between Mohr’s method and Volhard’s method?
Mohr’s method is a direct titration that uses Ag⁺ as titrant with chromate indicator in a neutral or slightly alkaline medium. Volhard’s method is an indirect (back) titration where excess Ag⁺ is first added and then titrated with thiocyanate (SCN⁻) using ferric alum indicator in an acidic medium.
Q2. What is Co-precipitation?
Co-precipitation is the contamination of a precipitate by substances that are normally soluble under the conditions of precipitation. It occurs during the formation of the precipitate.
Q3. What is Masking and Demasking?
In complexometric titration, masking agents prevent interfering ions from reacting with EDTA. Demasking agents later release the masked ion for titration. Example: CN⁻ masks Zn²⁺ and Cd²⁺; HCHO demasks Zn²⁺.
Q4. How does Fajan’s Method work?
Fajan’s method uses adsorption indicators (such as fluorescein). At the end point, the indicator gets adsorbed on the surface of the precipitate, producing a distinct color change.
Q5. What is Diazotisation Titration?
Diazotisation titration involves the reaction of primary aromatic amines (e.g., sulfonamides) with sodium nitrite (NaNO₂) in an acidic medium at low temperature (0–5°C) to form a diazonium salt.