Chapter 12: Gravimetric Methods of Analysis CHE 321: Quantitative Chemical Analysis Dr. Jerome Williams, Ph.D. Saint Leo University

Overview Gravimetric Analysis Precipitating Agents Applications of Gravimetric Methods

Gravimetric Analysis Formation and growth of crystals are very important in analytical chemistry and other areas of science.

Gravimetric Analysis Gravimetric methods are based on determining mass of a pure compound to which the analyte is chemically related. Types of analysis – Precipitation gravimetryVolatilization gravimetry – Gravimetric TitrimetryElectrogravimetry – Atomic Mass Spectrometry

Gravimetric Analysis Precipitation gravimetry: – A precipitating agent should react specifically or at least selectively with the analyte. – Characteristics of ideal precipitating agent 1. Easily filtered & washed free of contaminants 2. Low solubility to minimize loss of sample 3. Unreactive with atmosphere. 4. Known chemical composition after dried or ignited

Gravimetric Analysis Particle Size & Filterability of Precipitates: – Larger particles generally more desirable. – Factors that determine Particle Size: 1. Colloidal vs. Crystalline suspensions 2. Relative supersaturation 3. Mechanism: Nucleation & Particle Growth

Figure 12-5 p289

Figure 12-6 p290

Table 12-1 p290

Table 12-2 p294

Table 12-3 p295

p295

p296

Table 12-4 p297

Figure 12-8 p298