Carbonate EDTA titration

Polymers may act as weak chelating agents and thus retain hardness salts in solution in BW. In this event the hardness as determined by EDTA titration is measurable, particular attention should be given to maintaining the recommended level of carbonate or phosphate. In appropriate circumstances, chelating agents may be used in place of phosphate. 

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. 

The B,P.C. eye-drops and eye lotions are simple solutions of zinc sulphate with one or more of the following substances sodium chloride, adrenaline solution, chlorbutol and boric acid. None of these substances interferes with the assay of zinc sulphate by EDTA titration, method (viii) a)y 1 ml 0 02M EDTA = 0-00575 g ZnS04,7H20 adrenaline solution tends to mask the end-point but the amount present in these preparations is not sufficient to prevent the end-point being readily detected. For titration take 30 ml of Eye-drops of Zinc Sulphate B,P.C. (0-25 per cent), 30 ml of Eye-drops of Zinc Sulphate and Adrenaline, B.P.C. (0-25 per cent), and 50 ml of Compound Eye Lotion of Zinc Sulphate, B.P,C, (0-34 per cent with 2 29 per cent of boric acid) if boric acid is to be determined in the last-mentioned preparation, the zinc must first be precipitated with sodium carbonate (see p. 134). 

In a back titration, a slight excess of the metal salt solution must sometimes be added to yield the color of the metal-indicator complex. Where metal ions are easily hydrolyzed, the complexing agent is best added at a suitable, low pH and only when the metal is fully complexed is the pH adjusted upward to the value required for the back titration. In back titrations, solutions of the following metal ions are commonly employed Cu(II), Mg, Mn(II), Pb(II), Th(IV), and Zn. These solutions are usually prepared in the approximate strength desired from their nitrate salts (or the solution of the metal or its oxide or carbonate in nitric acid), and a minimum amount of acid is added to repress hydrolysis of the metal ion. The solutions are then standardized against an EDTA solution (or other chelon solution) of known strength. 

Commercial Hquid sodium alumiaates are normally analyzed for total alumiaa and for sodium oxide by titration with ethylene diaminetetraacetic acid [60-00-4] (EDTA) or hydrochloric acid. Further analysis iacludes the determiaation of soluble alumiaa, soluble siHca, total iasoluble material, sodium oxide content, and carbon dioxide. Aluminum and sodium can also be determiaed by emission spectroscopy. The total iasoluble material is determiaed by weighing the ignited residue after extraction of the soluble material with sodium hydroxide. The sodium oxide content is determiaed ia a flame photometer by comparison to proper standards. Carbon dioxide is usually determiaed by the amount evolved, as ia the Underwood method. 

Notes. (1) Somewhat sharper end points may be obtained if the sample of water is first acidified with dilute hydrochloric acid, boiled for about a minute to drive off carbon dioxide, cooled, neutralised with sodium hydroxide solution, buffer and indicator solution added, and then titrated with EDTA as above. 

Applications Basic methods for the determination of halogens in polymers are fusion with sodium carbonate (followed by determination of the sodium halide), oxygen flask combustion and XRF. Crompton [21] has reported fusion with sodium bicarbonate for the determination of traces of chlorine in PE (down to 5 ppm), fusion with sodium bisulfate for the analysis of titanium, iron and aluminium in low-pressure polyolefins (at 1 ppm level), and fusion with sodium peroxide for the complexometric determination using EDTA of traces of bromine in PS (down to 100ppm). Determination of halogens in plastics by ICP-MS can be achieved using a carbonate fusion procedure, but this will result in poor recoveries for a number of elements [88]. A sodium peroxide fusion-titration procedure is capable of determining total sulfur in polymers in amounts down to 500 ppm with an accuracy of 5% [89]. 

What is the titer (expressed in milligrams per milliliter) of a solution of disodium dihydrogen ethylenediaminetetraacetate (EDTA) with respect to calcium carbonate if 17.29 mL of it was needed to titrate 0.0384 g of calcium carbonate ... 

After equilibrium, filtration, and pH adjustment, the residual calcium ion concentration was then titrated by EDTA solution. A higher residual calcium ion concentration indicates better inhibition activity and, therefore, more effectiveness in controlling calcium carbonate deposition in the treated water. As shown in Table III, at dosages of 1 to 5 ppm, the polyacrylic acid was more effective than the acrylic acid/N-(hydroxyalkyl)-acrylamide copolymers. 

Titration with EDTA is used in the pharmacopoeial assays of bismuthsubcarbonate, calcium acetate, calcium chloride, calcium gluconate, magnesium carbonate, magnesium hydroxide, magnesium trisilicate, bacitracin zinc, zinc chloride and zinc undecanoate. 

Singhal et al. [306] have determined oxamyl residues (methyl-N. N -dimclh-yl-N- [methylcarbamoyl] oxy-thioaminimidate) by a method based on reaction with carbon disulfide and copper in which excess copper is added to an extract of the soil and the excess copper is determined by titration with 0.001 M EDTA to the l-(2-pyridylazo)-2-naphthol endpoint. 

The USP [2] describes a method for the titration of EDTA, using a weighed amount of chelometric standard calcium carbonate previously dried. The weight of edetate disodium (in mg) is calculated using the following formula ... 

Numerous tertiary amines that also contain carboxylic acid groups form remarkably stable chelates with many metal ions. Ethylenediamine tetra-acetic acid (EDTA) can be used for determination of 40 elements by direct titration using metal-ion indicators for endpoint detection. Direct titration procedures are limited to metal ions that react rapidly with EDTA. Back titration procedures are useful for the analysis of cations that form very stable EDTA complexes and for which a satisfactory indicator is not available. EDTA is also used for determining water hardness the total concentration of calcium and magnesium expressed in terms of the calcium carbonate equivalent. 

An alternative method is to add a small amount of Mg " to the EDTA solution. This immediately reacts with EDTA to form MgY with very little free Mg " in equilibrium. This, in effect, reduces the molarity of the EDTA. So the EDTA is standardized after adding the Mg " by titrating primary standard calcium carbonate (dissolved in HCl and pH adjusted). When the indicator is added to the calcium solution, it is pale red. But as soon as the titration is started, the indicator is complexed by the magnesiiim and turns wine red. At the end point, it changes to blue, as the indicator is displaced from the magnesium. No correction is required for the Mg added because it is accounted for in the standardization. This solution should not be used to titrate metals other than calcium. 

Hardness of water is usually expressed by assuming that all the hardness is due to dissolved calcium carbonate, which is present as ions. It can be estimated by titration with a standard soap solution or with edta. See also water softening. 

The determination of calcium in meat products, especially in mechanically recovered (or separated) meat (MRM/MSM), is an important estimation of the amount of bone material included in the meat. The AOAC method describes an acid digestion of the sample and reaction of an aliquot of the filtered digest with excess ethylenediaminetetraacetic acid (EDTA) under alkaline conditions to form a chelated complex with calcium ion. The excess EDTA is then titrated with calcium carbonate using hydroxynaph-thol blue as indicator. 

Titrimetric determination The mannitol or glycerol acid-base titration procedure is applied to the dissolved sodium carbonate melt for the determination of milligram amounts of B2O3. A blank prepared from a glass that does not contain boric oxide should be subjected to the same procedure. There are certain interferences the effect of fluoride is eliminated by adding calcium carbonate to the fusion mixture lead and zinc can be filtered off after dissolution of the melt phosphate is precipitated by addition of iron(ni) chloride. The influence of some interference from such elements as aluminum or titanium can be eliminated by adding ethylenediaminetetraacetic acid (EDTA). 

Study of a system of sodium carbonate and Rm2 sodium silicate from a concentrated solution with 45% dry extract (2Si02, Na20). (We shall see in the section on silicates that the nature of the original silicate plays an important role.) The experimental study of the postreaction species obtained was carried out by filtration, potentiometric titration by specific electrode, and complexo-metric titration by EDTA. At equilibrium, the calcium is found in three different forms whose relative proportions vary considerably with the silicate/carbonate proportion ... 

General methods for the estimation of bismuth present in quantity include direct weighing as sulphide precipitation as sulphide, conversion to carbonate and ignition to oxide and precipitation as phosphate. Recently the use of EDTA as a titrant for bismuth has considerably simplified the determination of this metal in pharmaceutical mixtures. Bismuth forms a complex at pH 1 to 2 and at this degree of acidity few other metals likely to be encountered (with the exception of iron) interfere bismuth may therefore be selectively titrated in the presence of, say, aluminium, magnesium, or calcium. Various methods available have been discussed by Brookes and Johnson and the following general procedure is recommended ... 

The magnesium carbonate is determined by igniting about 2 g in a silica dish, dissolving the residue in the minimum volume of dilute hydrochloric acid and diluting to 100 ml with water. 10 ml of this dilution is titrated with 0 05M EDTA as above. 

Pipette 25.00 cm of standard 0.10 M calcium salt solution into a 250 cm conical flask. Dilute to about 100 cm and add 2 cm of the magnesium complexonate suspension (shake before use), 5 cm of the buffer solution (pH = 10) and 2-3 drops of Erochrome Black T indicator. Titrate with the approximately 0.1 M EDTA solution to a steel blue end point. Repeat to obtain concordant results. Calculate, from the average titre, the concentration of EDTA as mol dmAlternatively use accurately weighed 0.2 g purest calcium carbonate dried at 105 C, add water and dil. HCl to dissolve. Boil to expel carbon dioxide dilute to 100 cm and continue as above. 

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