Chapter 27 Gravimetric and Combustion Analysis Dr S
Chapter 27 Gravimetric and Combustion Analysis Dr. S. M. Condren
Representative Gravimetric Analyses Dr. S. M. Condren
Dr. S. M. Condren
Dr. S. M. Condren
Precipitation Ag. NO 3 + Na. Cl -----> Ag. Cl + Na. NO 3 Dr. S. M. Condren
Precipitation Ag. NO 3 + Na. Cl -----> ? Ag. NO 3 + Na. Cl -----> Ag. Cl + Na. NO 3 total ionic equation Ag+ + NO 3 - + Na+ + Cl-----> Ag. Cl + Na+ + NO 3 net ionic equation Ag+ + Cl- -----> Ag. Cl Dr. S. M. Condren
Precipitation. WHY? Solubility Rules 1. The common salts of the alkali metals (Group IA) and the ammonium ion (NH 4+) are soluble. 2. Salts of nitrate (NO 3 -), chlorate (Cl. O 3 -), perchlorate (Cl. O 4 -), and acetate (CH 3 COO-) anions are soluble. 3. All chlorides, bromides, and iodides are soluble, except those of Ag+, Pb+2, and Hg 2+2 (the form that Hg(I) exists in water). Dr. S. M. Condren
Precipitation. WHY? Solubility Rules 4. Sulfates (SO 4 -2) are soluble except those of Ba+2, Pb+2, Hg+2, and Hg 2+2. Dr. S. M. Condren
Precipitation. WHY? Solubility Rules 5. Most metal hydroxides are insoluble. The exceptions are the hydroxides of the alkali metals and the heavier alkaline earth metals (Ca, Sr, Ba). 6. All carbonates (CO 3 -2) and phosphates (PO 4 -3) are insoluble, except those of the Group IA metals and NH 4+ ions. Dr. S. M. Condren
Crystal Growth nucleation particle growth supersaturated Dr. S. M. Condren
Crystal Growth relative supersaturation = (Q - S)/S where Q => actual concentration S => equilibrium concentration Dr. S. M. Condren
Crystal Growth techniques to promote crystal growth 1. Raising the temperature to increase S and thereby decrease relative supersaturation. 2. Adding precipitant slowly with vigorous mixing, to avoid a local, highly supersaturated condition where the stream of precipitant first enters the analyte. 3. Keeping the volume of solution large so that the concentration of analyte and precipitant are low. Dr. S. M. Condren
Dr. S. M. Condren
Precipitation in the Presence of Electrolyte coagulate => “to change or be changed from a liquid into a thickened mass” Dr. S. M. Condren
Precipitation in the Presence of Electrolyte Dr. S. M. Condren
Precipitation in the Presence of Electrolyte adsorption => attached to surface absorption => penetration beyond surface Dr. S. M. Condren
Digestion process of keeping mixture warm while the size of the crystals increase Dr. S. M. Condren
Purity absorbed impurities inclusions - impurity ions which randomly occupy sites in the crystal lattice occulusions - pockets of impurity trapped inside growing crystal coprecipitaion Dr. S. M. Condren
Purity gathering agent - precipitating agent used to collect trace component (process gathering) masking agent post-precipitation peptization Dr. S. M. Condren
Product Composition • • product must be of known composition hygroscopic substance ignition thermogravimetric Dr. S. M. Condren
Thermogravimetric curve for calcium salicylate Dr. S. M. Condren
Example: What weight of Fe 2 O 3 can be obtained from 1. 63 g of Fe 3 O 4? 2 Fe 3 O 4 + [O] -----> 3 Fe 2 O 3 (1. 63 g Fe 2 O 3) #g Fe 2 O 3 = ---------- Dr. S. M. Condren
Example: What weight of Fe 2 O 3 can be obtained from 1. 63 g of Fe 3 O 4? 2 Fe 3 O 4 + [O] -----> 3 Fe 2 O 3 (1. 63 g Fe 2 O 3)(1 mole Fe 3 O 4) #g Fe 2 O 3 = -------------------(231. 54 g Fe 3 O 4) Dr. S. M. Condren
Example: What weight of Fe 2 O 3 can be obtained from 1. 63 g of Fe 3 O 4? 2 Fe 3 O 4 + [O] -----> 3 Fe 2 O 3 (1. 63)(1 mole Fe 3 O 4)(3 mole Fe 2 O 3) #g Fe 2 O 3 = ---------------------(231. 54)(2 mole Fe 3 O 4) Dr. S. M. Condren
Example: What weight of Fe 2 O 3 can be obtained from 1. 63 g of Fe 3 O 4? 2 Fe 3 O 4 + [O] -----> 3 Fe 2 O 3 (1. 63)(1)(3 mole. Fe 2 O 3)(159. 69 g. Fe 2 O 3) #g Fe 2 O 3 = ------------------------(231. 54)(2) (1 mol Fe 2 O 3) Dr. S. M. Condren
Example: What weight of Fe 2 O 3 can be obtained from 1. 63 g of Fe 3 O 4? 2 Fe 3 O 4 + [O] -----> 3 Fe 2 O 3 (1. 63)(1)(3)(159. 69 g. Fe 2 O 3) #g Fe 2 O 3 = ------------------ = 1. 69 g (231. 54)(2)(1) Dr. S. M. Condren
EXAMPLE: What mass of Pb. I 2 will precipitate if 2. 85 g Pb(NO 3)2 is added to 225 m. L of 0. 0550 M KI(aq)? Pb(NO 3)2 + 2 KI ------> Pb. I 2 + 2 KNO 3 Dr. S. M. Condren
EXAMPLE: What mass of Pb. I 2 will precipitate if 2. 85 g Pb(NO 3)2 is added to 225 m. L of 0. 0550 M KI(aq)? Pb(NO 3)2 + 2 KI ------> Pb. I 2 + 2 KNO 3 if use all of the 2. 85 g Pb(NO 3)2 Dr. S. M. Condren
EXAMPLE: What mass of Pb. I 2 will precipitate if 2. 85 g Pb(NO 3)2 is added to 225 m. L of 0. 0550 M KI(aq)? Pb(NO 3)2 + 2 KI ------> Pb. I 2 + 2 KNO 3 if use all of the 2. 85 g Pb(NO 3)2 (2. 85 g Pb(NO 3)2 #g Pb. I 2 = ------------Dr. S. M. Condren
EXAMPLE: What mass of Pb. I 2 will precipitate if 2. 85 g Pb(NO 3)2 is added to 225 m. L of 0. 0550 M KI(aq)? Pb(NO 3)2 + 2 KI ------> Pb. I 2 + 2 KNO 3 if use all of the 2. 85 g Pb(NO 3)2 (2. 85 g Pb(NO 3)2)(1 mol Pb(NO 3)2 #g Pb. I 2 = ----------------------(331 g Pb(NO 3)2) Dr. S. M. Condren
EXAMPLE: What mass of Pb. I 2 will precipitate if 2. 85 g Pb(NO 3)2 is added to 225 m. L of 0. 0550 M KI(aq)? Pb(NO 3)2 + 2 KI ------> Pb. I 2 + 2 KNO 3 if use all of the 2. 85 g Pb(NO 3)2 (2. 85 g Pb(NO 3)2)(1 mol Pb(NO 3)2 #g Pb. I 2 = ----------------------(331 g Pb(NO 3)2) Dr. S. M. Condren
EXAMPLE: What mass of Pb. I 2 will precipitate if 2. 85 g Pb(NO 3)2 is added to 225 m. L of 0. 0550 M KI(aq)? Pb(NO 3)2 + 2 KI ------> Pb. I 2 + 2 KNO 3 if use all of the 2. 85 g Pb(NO 3)2 (2. 85)(1 mol Pb(NO 3)2)(1 mol Pb. I 2) #g Pb. I 2 = ----------------------(331) (1 mol Pb(NO 3)2) Dr. S. M. Condren
EXAMPLE: What mass of Pb. I 2 will precipitate if 2. 85 g Pb(NO 3)2 is added to 225 m. L of 0. 0550 M KI(aq)? Pb(NO 3)2 + 2 KI ------> Pb. I 2 + 2 KNO 3 if use all of the 2. 85 g Pb(NO 3)2 (2. 85)(1)(1 mol Pb. I 2)(461 g Pb. I 2) #g Pb. I 2 = ----------------------(331) (1 mol Pb. I 2) Dr. S. M. Condren
EXAMPLE: What mass of Pb. I 2 will precipitate if 2. 85 g Pb(NO 3)2 is added to 225 m. L of 0. 0550 M KI(aq)? Pb(NO 3)2 + 2 KI ------> Pb. I 2 + 2 KNO 3 if use all of the 2. 85 g Pb(NO 3)2 (2. 85)(1)(1 mol Pb. I 2)(461 g Pb. I 2) #g Pb. I 2 = ----------------------(331) (1 mol Pb. I 2) Dr. S. M. Condren
EXAMPLE: What mass of Pb. I 2 will precipitate if 2. 85 g Pb(NO 3)2 is added to 225 m. L of 0. 0550 M KI(aq)? Pb(NO 3)2 + 2 KI ------> Pb. I 2 + 2 KNO 3 if use all of the 2. 85 g Pb(NO 3)2 (2. 85)(1)(1)(461 g Pb. I 2) #g Pb. I 2 = ---------------- = 3. 97 g (331)(1)(1) Dr. S. M. Condren
Dr. S. M. Condren
Dr. S. M. Condren
Dr. S. M. Condren
Dr. S. M. Condren
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