Sulfate EDTA titration

EDTA titrations are routinely used to determine water hardness in a laboratory. Raw well water samples can have a significant quantity of dissolved minerals that contribute to a variety of problems associated with the use of such water. These minerals consist chiefly of calcium and magnesium carbonates, sulfates, etc. The problems that arise are mostly a result of heating or boiling the water over a period of time such that the water is evaporated, and the calcium and magnesium salts become concentrated and precipitate in the form of a scale on the walls of the container, hence the term hardness. This kind of problem is evident in boilers, domestic and commercial water heaters, humidifiers, tea kettles, and the like. 

Oxamyl (melhyl-N.N -dimethyl-N- [ (methyl-carbarn oyl)oxy] -1 -thio oxamidate) Plants including leaves, potato, tomato and wheat Ethyl acetate extraction of sample Addition of excess copper sulfate, back-titration with standard EDTA to 1 -(2-pyridylazo)2-naphthol [61]... 

FIGURE 14-13 Photometric titration curves (a) total hardness of water, (b) determination of sulfate. In (a), total water hardness is obtained by titration with 0.10 M EDTA at 610 nm for 100 mL of a solution that contained 2.82 mmol/L total hardness. Eriochrome Black T was the indicator. In (b), 10.0 mU of a solution containing sulfate was titrated with 0.050 M BaCl2 using Thorin as an indicator and a wavelength of 523 nm. The response shown is proportional to transmittance. (From A. L Underwood, Anal. Chem., 1954,26,1322. Figure 1, p. 1323. Copyright 1954 American Chemical Society.)... 

Manganese(II) can be titrated directly to Mn(III) using hexacyanoferrate(III) as the oxidant. Alternatively, Mn(III), prepared by oxidation of the Mn(II)-EDTA complex with lead dioxide, can be determined by titration with standard iron(II) sulfate. 

Standard EDTA Solutions. Disodium dihydrogen ethylenediaminetetraacetate dihydrate is available commercially of analytical reagent purity. After drying at 80°C for at least 24 hr, its composition agrees exactly with the dihydrate formula (molecular weight 372.25). It may be weighed directly. If an additional check on the concentration is required, it may be standardized by titration with nearly neutralized zinc chloride or zinc sulfate solution. 

Lebel [224] has described an automated chelometric method for the determination of sulfate in seawater. This method utilises the potentiometric end-point method for back titration of excess barium against EDTA following precipitation of sulfate as barium sulfate. An amalgamated silver electrode was used in conjunction with a calomel reference electrode in an automatic titration assembly consisting of a 2.5 ml autoburette and a pH meter coupled to a recorder. Recovery of added sulfate was between 99 and 101%, and standard deviations of successive analyses were less than 0.5 of the mean. 

In an experiment to determine the percentage of nickel In hydrated nlckel(ll) sulfate, 2-63 g of the nlckel(ll) sulfate were weighed accurately, dissolved In water and diluted to 100 cm in a standard flask. A 20-0 cm volume of this solution was pipetted Into a conical flask along with an indicator solution. This solution was titrated against a 0-100 mol fi EDTA solution until the end-point was observed. The titrations were repeated until concordant results were obtained. 

Anions that precipitate with certain metal ions can be analyzed with EDTA by indirect titration. For example, sulfate can be analyzed by precipitation with excess Ba2+ at pH 1. 

Other typical reagents generated for coulometric titrations are hydrogen and hydroxyl ions, redox reagents such as ceric, cuprous, ferrous, chromate, ferric, manganic, stannous, and titanous ions, precipitation reagents such as silver, mercurous, mercuric, and sulfate ions, and complex-formation reagents such as cyanide ion and EDTA [8-10]. 

Issa et al. [9] used various metal ions for the volumetric determination of mefenamic acid. Mefenamic acid was precipitated from its neutral alcoholic solution by a standard solution of either silver nitrate, mercurous acetate, or potassium aluminum sulfate. In the argentimetric procedure, residual Ag(I) was titrated with standard NH4SCN. With Hg(OAc)2 or potash alum, the residual metal was determined by adding EDTA and conducting back titration of excess of EDTA with standard Pb(N03)2 using xylenol orange indicator. The applied methods were used for the determination in bulk drug substance, and in its formulations. 

Assay Dissolve about 1 g of sample, accurately weighed, in 50 mL of water, add 50.0 mL of 0.05 M disodium EDTA and 20 mL of pH 4.5 buffer solution (77.1 g of ammonium acetate and 57 mL of glacial acetic acid in 1000 mL of aqueous solution), and boil gently for 5 min. Cool, and add 50 mL of alcohol and 2 mL of dithizone TS. Back titrate with 0.05 M zinc sulfate to a bright rose-pink color. Perform a blank determination (see General Provisions), and make any necessary correction. The milliliters of 0.05 M disodium EDTA consumed is equivalent to 50 minus the milliliters of 0.05 M zinc sulfate used. Each milliliter of 0.05 M disodium EDTA is equivalent to 23.72 mg of A1K(S04)2T2H20. Ammonium Salts Add 1 g of sample to 10 mL of 1 N sodium hydroxide in a small beaker, and heat on a steam bath for 1 min. The odor of ammonia is not perceptible. Fluoride Determine as directed in Method V under Fluoride Limit Test, Appendix IIIB. 

Calcium Content Dissolve about 1.5 g of sample, accurately weighed, in 100 mL of water containing 2 mL of 2.7 A hydrochloric acid. While stirring, preferably with a magnetic stirrer, add about 30 mL of 0.05 M disodium EDTA from a 50-mL buret, then add 15 mL of 1 A sodium hydroxide and 300 mg of hydroxy naphthol blue indicator, and continue the titration to a blue endpoint. Each milliliter of 0.05 M disodium EDTA is equivalent to 2.004 mg of calcium (Ca). Halides Determine as directed in the Chloride Limit Test under Chloride and Sulfate Limit Tests, Appendix IIIB. A 1.2-g sample shows no more turbidity than 0.7 mL of 0.020 A hydrochloric acid. 

Titer Determination Pipet 50.0 mL of Magnesium Sulfate Solution into a 400-mL beaker, and add 200 mL of water, 2 mL of Buffer Solution Initial Preparation, 1.0 mL of a 1 20 potassium cyanide solution, and 5 drops of eriochrome black TS or another suitable indicator. While stirring with a magnetic stirrer, titrate with the Standard EDTA Solution to a true blue endpoint. Record the volume, / , in milliliters, of Standard EDTA Solution equivalent to 50.0 mL of Magnesium Sulfate Solution. 

Add 2 g of sodium fluoride, boil the mixture for 2 to 5 min, and cool in a stream of running water. Titrate the EDTA (which is released by fluoride from its aluminum complex) with 0.01 M Zinc Sulfate to the same transitory yellow-brown or pink endpoint as described above. 

Zinc Sulfate, 0.05 M (8.072 g ZnS04 per 1000 mL) Dissolve about 15 g of zinc sulfate (ZnS04-7H20) in sufficient water to make 1000 mL, and standardize the solution as follows Dilute about 35 mL, accurately measured, with 75 mL of water, add 5 mL of Ammonia-Ammonium Chloride Buffer TS and 0.1 mL of Eriochrome Black TS, and titrate with 0.05 M Disodium EDTA until the solution is deep blue. Calculate the molarity. 

Masking can be achieved by precipitation, complex formation, oxidation-reduction, and kinetically. A combination of these techniques may be employed. For example, Cu " can be masked by reduction to Cu(I) with ascorbic acid and by complexation with I . Lead can be precipitated with sulfate when bismuth is to be titrated. Most masking is accomplished by selectively forming a stable, soluble complex. Hydroxide ion complexes aluminum ion [Al(OH)4 or AlOa"] so calcium can be titrated. Fluoride masks Sn(IV) in the titration of Sn(II). Ammonia complexes copper so it cannot be titrated with EDTA using murexide indicator. Metals can be titrated in the presence of Cr(III) because its EDTA chelate, although very stable, forms only slowly. 

The adsorption experiments were performed as follows 0.100 g of the hexagonal templated zirconia matrix was suspended, under magnetic stirring, for 60 min, into 20 cm of an aqueous solutions of Co(II), Ni(II), Cu(II), and Zn(II) previously-prepared by dissolution of the respective sulfates (with exception of cobalt, for which chloride was used). The flasks containing the suspensions were kept on a water bath at controlled temperature (25 0.5°C). The total amount of metal cations before and after the adsorption process was measured for each individual cation, by volumetric titration with a 3.2x10 mol dm EDTA solution. 

Chromium oxide (Cr203). Up to 0.1% colorimetrically with diphenylcarbizide at 540 nm. Above 0.1% but as a minor constituent, colorimetrically with EDTA at 550 nm. As a major constituent by oxidation to dichromate by peroxodisulfuric acid using a silver nitrate catalyst, destruction of permanganate with HCl and titration against ferrous ammonium sulfate using diphenylamine-4-sulfonate indicator. 

Anions that precipitate metal ions can be analyzed with EDTA by indirect titration. For example, sulfate can be analyzed by precipitation with excess Ba at pH 1. The resulting BaS04( ) is filtered, washed, and boiled with excess EDTA at pH 10 to bring Ba back into solution as Ba(EDTA). The excess EDTA is back titrated with Mg. ... 

After converting silica to alpha-12 molybdosilicic acid, the latter can be titrated with ferrous sulfate in the presence of EDTA, tartaric acid, and chloroacetic acid buffer at pH 2.5, The end point is determined amperometrically with two platinum electrodes (332). 

It requires 31.5 mL of 0.0104 M [EDTA] solution to reach the end point in the titration. A second 0.100-L sample was then treated with sulfate ion to precipitate Ca as calcium sulfate. The Mg was then titrated with 18.7 mL of 0.0104 M [EDTA] . Calculate the concentrations of and Ca in the hard water in mg/L. 

---