Unit 22
Titrimetric and gravimetric analysis
Classical chemical analysis still anchors many standard methods. Starting from primary standards and volumetric glassware, this unit measures water hardness with EDTA, computes redox titration curves from the Nernst equation, determines chloride in seawater by argentometry, and ends by heating precipitates to constant mass and watching them lose weight on a thermobalance — every curve and colour computed from equilibrium models, every unknown waiting for you to measure it.
- 1 Volumetric analysis: primary standards and standardisation The 0.1 M on the label is never 0.1000 M. Standardise titrants against primary standards such as KHP, master burettes and pipettes, and see where the uncertainty comes from. 25 min
- 2 Kjeldahl nitrogen: from nitrogen to protein How is the protein on a food label measured? Digestion, distillation and titration measure nitrogen, and a conversion factor turns it into protein. Use Jones’s 1931 data to see when 6.25 goes wrong, and why melamine could fool the method. 30 min
- 3 Complexometric titration: EDTA and water hardness One molecule grabs almost every metal ion, yet is fussy about pH. Conditional formation constants, the wine red and pure blue of Eriochrome Black T, and the hardness of a tap water. 30 min
- 4 Redox titrations Permanganate is its own indicator, dichromate needs phosphoric acid, and starch waits until the iodine is pale yellow. Potential curves and equivalence potentials computed point by point from the Nernst equation. 30 min
- 5 Precipitation titration: argentometry Mohr, Volhard and Fajans: three quite different endpoints for one job — chloride in seawater. The pAg curves come from solubility products. 25 min
- 6 Gravimetric analysis An “absolute” method with no calibration curve: control supersaturation for a good precipitate, digest, wash, ignite to constant mass, and use gravimetric factors for sulfate and nickel. 25 min
- 7 Thermogravimetry What does a precipitate turn into when it is ignited? A thermobalance weighs while it heats: calcium oxalate loses water, carbon monoxide and carbon dioxide in turn. Step heights are stoichiometry, step temperatures are kinetics — two heating rates give an activation energy. 25 min