BP106T • Unit 5Topic 3 of 3⏱ 5 Min Read

3. Gravimetric Analysis: Principles & Assay of Barium as Barium Sulphate

💡 Core Concept & Clinical Context:

Gravimetric Analysis is a classical quantitative analytical technique based on the separation of an analyte from solution as a sparingly soluble, chemically stable precipitate, followed by filtration, washing, thermal drying or high-temperature furnace ignition, and highly accurate weighing on an analytical balance. Gravimetric steps strictly follow: (1) Sample Dissolution $\rightarrow$ (2) Precipitation with excess precipitating reagent $\rightarrow$ (3) Digestion / Ostwald Ripening (heating on a water bath below boiling for 1-2 hours to dissolve small unstable micro-crystals and recrystallize onto larger, purer crystal lattices, reducing co-precipitation) $\rightarrow$ (4) Filtration using Ashless Filter Paper (Whatman No. 42) $\rightarrow$ (5) Washing to remove adsorbed impurities $\rightarrow$ (6) Drying and Ignition in a tared silica crucible at 800-900°C $\rightarrow$ (7) Cooling in a desiccator and weighing to constant mass.

Clinical Scenarios & Pharmacopoeial Examples:

1Gravimetric Assay of Barium Sulphate ($BaSO_4$)

Standard calculation using the Gravimetric Factor.

Step-by-Step Breakdown:

•Chemical Reaction:

•BaCl2 + H2SO4 (dilute, hot) --[Digestion at 80-90°C]--> BaSO4 v (Heavy white precipitate) + 2 HCl

•Gravimetric Factor (GF):

•GF = [ Molecular Weight of Analyte (Ba) ] / [ Molecular Weight of Weighed Precipitate (BaSO4) ]

•GF = 137.33 / 233.39 = 0.5884

•Worked Calculation:

•• Weight of sample containing Barium = 0.5000 g

•• Weight of ignited empty crucible = 18.4520 g

•• Weight of crucible + ignited BaSO4 = 18.8945 g

•• Weight of pure BaSO4 precipitate = 18.8945 - 18.4520 = 0.4425 g

•Weight of Barium in Sample = Weight of BaSO4 * GF

•Weight of Barium = 0.4425 g * 0.5884 = 0.2604 g Ba

•Percentage of Barium in Sample = (0.2604 g / 0.5000 g) * 100 = 52.08%

📋Key Takeaways & Exam Highlights

Digestion (Ostwald Ripening): Minimizes co-precipitation (inclusion/occlusion) and produces large, easily filterable crystalline precipitates.
Ashless Filter Paper: Leaves less than 0.0001 g of ash residue upon combustion in a furnace.
Coprecipitation: Contamination of precipitate by substances that are normally soluble under experimental conditions (Occlusion, Surface adsorption, Isomorphous inclusion).
Postprecipitation: Deposition of a second, normally soluble substance onto the primary precipitate surface after a prolonged delay (e.g., $MgC_2O_4$ depositing onto $CaC_2O_4$).

🇮🇳 हिन्दी व्याख्या (3. Gravimetric Analysis: Principles & Assay of Barium as Barium Sulphate)

ग्रेविमीट्रिक एनालिसिस (Gravimetric Analysis) में दवा को अघुलनशील अवक्षेप (जैसे BaSO4) बनाकर छाना, 800°C पर जलाया और सटीक वजन नापकर शुद्धता निकाली जाती है। डाइजेशन (Digestion) से अवक्षेप के कण बड़े और शुद्ध बनते हैं।