Part I. A system of elemental analysis. Part II. The standard potential of the iodine-iodine monocyanide half cell. Part III. The use of thioacetamide for the homogenous phase precipitation of inorganic sulfides
NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. A system of elemental analysis for pedagogical use has been developed. Non-metallic solids are fused with sodium hydroxide, sodium carbonate and sodium nitrate and the melt is treated...
| Summary: | NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.
A system of elemental analysis for pedagogical use has been developed. Non-metallic solids are fused with sodium hydroxide, sodium carbonate and sodium nitrate and the melt is treated with water to give a residue of the basic element oxides, hydroxides and carbonates, and a solution containing the amphoteric and acidic elements. Metallic solids are dissolved in nitric acid and the hot solution is treated with sodium chlorate. The solution is made alkaline with sodium hydroxide and the separation into groups is the same as is obtained by the fusion treatment. The procedures are capable of yielding semi-quantitative results and thus they permit approximate estimation of the elements.
The standard potential of the iodine-iodine monocyanide half cell has been determined. Measurements were made through the concentration ranges 0.2 to 4 F HClO4 and 0.06 to 0.3 F total cyanide and the value -0.6248 [plus or minus] 0.0026 v was obtained for the potential. The constant for the disproportionation of iodine in hydrocyanic acid solutions was determined by solubility measurements to be 0.870 [plus or minus] 0.009.
The hydrolysis of thioacetamide to acetamide and hydrogen sulfide in dilute acid solutions was found to be first order with respect to both thioacetamide and hydrogen ion concentrations; under the conditions of the experiments in this study only a small fraction of the acetamide formed was hydrolyzed to acetic acid and ammonia. The second order rate constant for the hydrolysis reaction was found to be 0.21 [plus or minus] 0.02 liter/mole minute at 90[degrees] C. The energy of activiation was determined and is 19.1 kcal mole through the temperature range from 60 [degrees] to 90 [degrees] C.
The precipitation of lead sulfide by thioacetamide was found to proceed through two distinct mechanisms depending upon the pH of the solution. At low pH the precipitation involves the hydrolysis of thioacetamide to give hydrogen sulfide which then reacts with the lead. At higher pH the rate of precipitation shows first order dependence upon both thioacetamide and lead ion concentrations and inverse half order dependence upon hydrogen ion concentration. The rate constant and energy of activation have been calculated to be 1.15 [plus or minus] 0.12 x 10[superscript -3] liter[superscript 1/2] mole[superscript -1/2] minute[superscript -1] and 15.5 kcal/mole respectively. A discussion of the analytical use of thioacetamide is presented. |
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