Sulfate gravimetric analysis

Wil Kastning of the Nebraska State Agriculture Laboratory filters barium sulfate precipitates using filtering crucibles and a vacuum system while performing a gravimetric analysis of fertilizers for sulfate content. 

Water of crystaUization in hydrated salts can be measured by thermo-gravimetric analysis. Zinc can be analyzed in an aqueous solution by AA or ICP. Sulfate can be identified by precipitation with barium chloride solution or by ion chromatography. The zinc content in the heptahydrate is determined by AA, ICP and other instrumental methods. 

S04 Sulfate 0 1, 0/ 0 0 Til symmetry, extremely common ion, used in gravimetric analysis... 

Microwave laboratory ovens are currently quite popular. Where applicable, these greatly shorten drying cycles. For example, slurry samples that require 12 to 16 hours for drying in a conventional oven are reported to be dried within 5 to 6 minutes in a microwave oven. The time needed to dry silver chloride, calcium oxalate, and barium sulfate precipitates for gravimetric analysis is also shortened significantly. ... 

We take advantage of the common ion effect to decrease the solubility of a precipitate in gravimetric analysis. For example, sulfate ion is determined by precipitating BaS04 with added barium chloride solution. Figure 10.3 illustrates the effect of excess barium ion on the solubility of BaS04. 

Actual electrolyte compositions were measured b gravimetric analysis of total sulfur species present after oxidation with hydrogen peroxide. A sample of membrane material was weighed and then dissolved in water. The insoluble matrix materials were filtered and the filtrate treated with excess hydrogen peroxide which oxidizes all sulfur species to sulfate. It was assumed t t oidy sulfur in the form of sulfide was present in the membrane under run conditions. This solution was then acidified with hydrochloric acid to decompose the carbonate to carbon dioxide and water. The solution was then boiled to de-gas the mixture... 

Barium is also notable for the very low solubility of the sulfate, which permits its application to gravimetric analysis for either barium or sulfate. Barium compounds give a characteristic green color to flames which is used in qualitative analysis. Barium salts are all highly toxic with the exception of the most insoluble materials. Metallic barium has the body-centered cubic structure. 

PURPOSE OP EXPERIMENT Prepare KA1(S04)2 12H20, an aluminum alum, from aluminum metal. (Note Experiment 14 describes the gravimetric analysis of the sulfate content in alum.)... 

In gravimetric analysis, the solution-preparation step has its own special significance. The analyte must be separated from interfering species, or the interferents must be masked. For example, if iron(III) is to be estimated as its hydrated oxide in the presence of chromium(III), then the mixture is initially treated with perchloric acid so as to oxidize chromium(III) to chromate (chromium(VI), Cr04 ), followed by addition of ammonia to precipitate the hydrated iron oxide. Sometimes it is necessary to remove interferents, for example, when calcium is to be estimated as calcium sulfate in the presence of barium. The barium is removed as its chromate and the calcium is precipitated quantitatively as its sulfate. 

As an example of a gravimetric analysis, consider the problem of determining the amount of lead in a sample of drinking water. Lead, if it occurs in the water, probably exists as the lead(II) ion, Pb. Lead(II) sulfate is a very insoluble compound of lead(II) ion. When sodium sulfate, Na2S04, is added to a solution containing Pb ", lead(II) sulfate precipitates (that is, PbS04 comes out of the solution as a fine, crystalline solid). If you assume that the lead is present in solution as lead(ll) nitrate, you can write the following equation for the reaction ... 

Titration with added sodium sulfate petroleum ether extraction from acidic ethanol/water Calculated from total and monosulfonate column chromatography separation Titration/gravimetric analysis HPLC... 

The copper content in cupric compounds is usually determined by gravimetric analysis. In the conventional method, Cu is usually reduced to Cu by the addition of sulfurous acid, ammonium hydrogen sulfite, ascorbic acid, or ferrous sulfate. It is then precipitated as cuprous thiocyanate by the addition of ammonium thiocyanate and estimated gravimetrically. 

Hydrazine sulfate is used as a reducing agent in analytical chemistry for gravimetric measurement of nickel, cobalt, and other metals, and in peptide analysis in the separation of polonium from tellurium as an antioxidant in... 

In the determination of sulfate, 2 to 5 g of the analysis sample is mixed with HC1 (2 volumes concentrated HC1 + 3 volumes of water), and the mixture is gently boiled for 30 minutes. After filtering and washing, the undissolved coal may be retained for the determination of pyrite sulfur, or it may be discarded and a fresh sample used for pyrite sulfur. Saturated bromine water is added to the filtrate to oxidize all sulfur forms to sulfate ions and ferrous ions to ferric ions. After boiling to remove excess bromine, the iron is precipitated with excess ammonia and filtered. This precipitate must be retained for the determination of nonpyrite iron if a fresh sample of coal was used for the determination of the pyrite iron. The sulfate is then precipitated with ISaCE, and the BaSC>4 is determined gravimetrically. 

Analysis of the compound for platinum is accomplished gravimetrically by reduction of a known weight of the anhydrous salt to metallic platinum with formic acid.3 For the determination of chloride, 0.3 g. of the anhydrous salt is dissolved in 40 ml. of distilled water containing 250 mg. of hydrazine sulfate the solution is boiled gently until platinum metal is formed and coagulated. Then, without removal of the platinum, the solution is made 1 f in nitric acid and is titrated potentiometrically with standard 0.2 F silver nitrate solution. Anal. Calcd. for Na2PtCl6 Pt, 42.99 Cl, 46.88. Found Pt, 42.78 Cl, 46.73. 

Section 12 of ASTM Chemical Analysis of Gypsum and Gypsum Products (C 471) deals with the determination of sulfur trioxide in gypsum gravimetrically. Basically, gypsum is dissolved in dilute hydrochloric acid, and sulfate is precipitated as barium sulfate by addition of hot/boiling barium chloride solution. 

Species analysis is performed with various analytical methods, and some examples are described in the following section. Sulfate can be determined depending on the amount in various waters (drinking, surface, waste and saline waters), either colorimetri-cally after reaction with chloranilate in forming the colored acid chloranilate ion, automated as methylthymol blue, as barium sulfate either gravimetrically or nephelometri-cally (turbidimetric) and directly with IC... 

Using the proper choice of separation column, ion chromatography appears to be applicable for the sequential multicomponent analysis of other anions such as sulfate, chloride, fluoride and nitrate. The detection limits will be substantially lower than the classical gravimetric and potentiometric methods currently used. Ion selective electrodes are available for chloride and fluoride. 

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