Sulfide precipitation titration

Aspirate through ammoniacal cadmium chloride strip sulfur dioxide by aeration dissolve cadmium sulfide precipitate in concentrated HC1 titrate with iodine using a starch indicator. Iodometric titration 0.7 qg/L NR EPA 1978... 

Presence of oxidizable substances in the sample would interfere in the test, thus giving high results. These include S2. S 0,2. and certain metal ions such as Fe2+ in lower oxidation state. Sulfide should be removed by adding 0.5 g zinc acetate, allowing the zinc sulfide precipitate to settle and drawing out the supernatant liquid for analysis. If thiosulfate is present, determine its concentration in an aliquot of sample by iodometric titration using iodine standard. Subract the concentration of thiosulfate from the iodometric sulfite results to calculate the true value of SO,2. ... 

During the acidic extractions evolving sulfide can be trapped in a separate alkaline solution (e.g. Sulfur Antioxidant Buffer, SAOB, Cornwell and Morse 1987) where it can be determined polarographically, by precipitation titration with Pb or by a standard ion sensitive electrode. Sulfide evolving from HCl extraction is called Acid Volatile Sulfur (AVS). 

The potentiometric detection of the endpoint of precipitation titrations is very often used because not many visual indicators are available, in particular when mixtures of analytes are titrated. Halides, cyanide, sulfide, chromate, mercaptans, and thiols can be titrated with silver nitrate, using the silver sulfide-based ISE. Also complex mixtures, such as sulfide, thiocyanide, and chloride ions, or chloride, bromide, and iodide ions, can be titrated potentio-metrically with silver(I) ions. When the solubility of a compound formed during titration is too high, nonaqueous or mixed solvents are used, for example,... 

Carbonate is measured by evolution of carbon dioxide on treating the sample with sulfuric acid. The gas train should iaclude a silver acetate absorber to remove hydrogen sulfide, a magnesium perchlorate drying unit, and a CO2-absorption bulb. Sulfide is determined by distilling hydrogen sulfide from an acidified slurry of the sample iato an ammoniacal cadmium chloride solution, and titrating the precipitated cadmium sulfide iodimetrically. 

The precipitated acetyHde must be decomposed with hydrochloric acid after the titration as a safety measure. Concentrated solutions of silver nitrate or silver perchlorate form soluble complexes of silver acetyHde (89). Ammonia and hydrogen sulfide interfere with the silver nitrate method which is less... 

Quantitative. Classically, silver concentration ia solution has been determined by titration with a standard solution of thiocyanate. Ferric ion is the iadicator. The deep red ferric thiocyanate color appears only when the silver is completely titrated. GravimetricaHy, silver is determined by precipitation with chloride, sulfide, or 1,2,3-benzotriazole. Silver can be precipitated as the metal by electro deposition or chemical reduciag agents. A colored silver diethjldithiocarbamate complex, extractable by organic solvents, is used for the spectrophotometric determination of silver complexes. 

At higher levels, cadmium may be estimated gravimetrically following precipitation with sulfide (20), P-naphthoquinoline (21), or after plating from a cyanide-containing solution onto a stationary platinum cathode. Volumetric procedures rely on preliminary precipitation of the sulfide that is purified and then dissolved in acid whereupon the liberated H2S may be titrated with iodine. An alternative, should zinc be a likely contaminant, is to precipitate with diethyldithiocarbamate and then to redissolve in acid and titrate with sodium ethylenetriaminetetraacetate (HDTA) using Eriochrome Black T as indicator (22). 

To a solution containing 25.00 mL of 0.043 32 M Cu(C104)2 plus 15 mL of 1 M acetate buffer (pH 4.5) were added 25.00 mL of unknown sulfide solution with vigorous stirring. The CuS precipitate was filtered and washed with hot water. Then ammonia was added to the filtrate (which contained excess Cu2+) until the blue color of Cu(NH3) + was observed. Titration with 0.039 27 M EDTA required 12.11 mL to reach the murexide end point. Calculate the molarity of sulfide in the unknown. 

In the titration of thioacetamide with silver nitrate in distilled water and in slightly acidic or basic solution, a black precipitate of silver sulfide formed. The other products of the reaction were ammonium nitrate and acetic acid. Two reaction pathways have been suggested for the course of this reaction, Scheme 3 and equation (24).349,330 In the presence of 0.1 MHN03, the reaction proceeded similarly. However, in 0.5 M or more concentrated HN03 solutions a different reaction took place. Under these conditions a light, pearly precipitate was formed and a silver thioacetamide complex was obtained. 

A measured amount of standard iodine solution is placed in a 500-mL flask. The amount of iodine should be the excess over the expected quantity of sulfide in the sample. Add distilled water and bring the volume to 20 mL. Add 2 mL of 6 A HC1. Pipette 200 mL of sample into the flask. If the sulfide in the sample was precipitated as ZnS, transfer the precipitate with 100 mL distilled water into the flask. Add iodide solution and HC1. If iodine color disappears, add more iodine standard solution into the flask, until the color remains. Titrate with Na2S203 standard. Before the end point, when the color changes to straw yellow or brown, add a few mL of starch solution and continue titration by dropwise addition of Na2S203 standard until the blue color disappears. Record the volume of titrant added. 

Sulfacetamide and other sulfonamides in pharmaceutical dosage forms have been determined with a silver sulfide electrode over the concentration range lO -lO 1 M. The sulfonamide is dissolved in dimethylformamide, 0.01 N silver nitrate is added, the solution filtered, and the resulting precipitate washed and the excess silver nitrate determined by potentiometric titration with 0.01 N sodium chloride (67,68). 

A new method for the determination sulfldes is based on titration by precipitation and fluorimetric detection of the end-point [102]. The indicator is a dye derived from acridine, the fluorescence of which is statically quenched by sulfide The concentrations measured range between 1 and 10 mM by titration with silver nitrate. 

The product is boiled with water, and the resulting precipitate of silver sulfide is collected by filtration, washed, dried, and weighed. Another sample of product is dissolved completely in concentrated nitric acid, any excess acid is removed by boiling, and the total silver ion is determined by titration with standard ammonium thiocyanate solution. Another sample of product is oxidized with concentrated nitric acid in a bomb tube, and after removal of silver and nitrate the sulfur is determined by precipitation as barium sulfate by addition of barium chloride solution. 

Given the vride variety of ion-selective electrodes already commercially available and the many more specialized ones that can be fabricated, titrations involving the precipitation or complexation of ions are widely used. Halides, cyanide, thiocyanate, sulfide, chromate, and thiols can be titrated with silver nitrate, using the appropriate... 

If the glass contains lead and/or barium oxide, the glass should be treated with a mixture of hydrofluoric and sulfuric acids and the insoluble lead and barium sulfates filtered off before the titration. Lead may also be precipitated with hydrogen sulfide. Small amounts of aluminum and iron may be masked with triethanolamine. Greater amounts of aluminum and iron must be preseparated by precipitation as their hydrated oxides in the procedure for gravimetric determination of alumina. If the content of iron oxide, alumina, and titania is large, they can be separated using a 25% solution of urotropin. 

Other example is the determination of fuel parameters including the diene value and mercaptan sulfur. First, the robot weighs the sample, refluxes it in the presence of maleic anhydride, and extracts the analytes into an aqueous phase, which is poured into the titration vessel, where the robot inserts the photometric or potentiometric probe. For the determination of mercaptan sulfur, the robot also weighs the sample and removes sulfide by precipitation with a CdS04 solution and liquid-liquid extraction. Once the fuel is sulfide free, which is checked by using a photometric probe, it is poured into the titration vessel by the robot arm, which also plunges an Ag electrode prior to addition of the titrant (an AgNOs solution). In both cases, the automated titrator acts as a module of the robotic station and is operated by the robotic arm. 

Precipitate and wash metal sulfide. Dissolve in 3 M HCl with excess standard 13 and back titrate with thiosulfate. 

Hartmann and Hillig (1930) found the potassium acid tartrate procedure unsatisfactory because when alcohol is added pectins and other colloidal materials are precipitated and occlude other acids. To avoid this they recommend adding alcohol first to remove the pectins and to precipitate the acids in the filtrate with lead acetate. The precipitate is then dissolved and treated with hydrogen sulfide to remove the lead. Recovery of 97% to 100.2% of the tartaric acid from mixtures with malic and citric acid was reported. The procedure of Beis (1934) for the determination of tartrates and tartaric acid is based on the relative insolubility of the tartrates in alcohol. Titration before and after removal of the tartrates was used to obtain the tartrates by difference. Other procedures appear to be more suitable. 

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