Ca titration with EDTA

Anthropogenic use of groundwater 3.1.5.1 Sampling Ca titration with EDTA... 

Murexide forms eomplexes with numerous metal eations such as Cu, Ni +, Co, and Ca + and ions deriving from lanthanides. The complex s color depends on the pH and the nature of metallie ions. Murexide permits Ca + titration with EDTA at pH = 11. As the figure shows, the eolor turns red from violet blue. 

Description of the Method. The operational definition of water hardness is the total concentration of cations in a sample capable of forming insoluble complexes with soap. Although most divalent and trivalent metal ions contribute to hardness, the most important are Ca + and Mg +. Hardness is determined by titrating with EDTA at a buffered pH of 10. Eriochrome Black T or calmagite is used as a visual indicator. Hardness is reported in parts per million CaCOs. 

Inorganic Analysis Complexation titrimetry continues to be listed as a standard method for the determination of hardness, Ca +, CN , and Ch in water and waste-water analysis. The evaluation of hardness was described earlier in Method 9.2. The determination of Ca + is complicated by the presence of Mg +, which also reacts with EDTA. To prevent an interference from Mg +, the pH is adjusted to 12-13, precipitating any Mg + as Mg(OH)2. Titrating with EDTA using murexide or Eri-ochrome Blue Black R as a visual indicator gives the concentration of Ca +. 

Determination of iron(III) in the presence of aluminium. Iron(III) (concentration ca 50 mg per 100 mL) can be determined in the presence of up to twice the amount of aluminium by photometric titration with EDTA in the presence of 5-sulphosalicylic acid (2 per cent aqueous solution) as indicator at pH 1.0 at a wavelength of 510 nm. The pH of a strongly acidic solution may be adjusted to the desired value with a concentrated solution of sodium acetate about 8-10 drops of the indicator solution are required. The spectrophotometric titration curve is of the form shown in Fig. 17.23. 

Fig. 5.11. Continuous monitoring of Ca by flow-rate titration with EDTA and using the Cd ISE and Cd EDTA as an electrometric indicator [105].

The complexometric method for determination of Ca(II) and Mg(II) is based on two titrations with EDTA in alkaline solution, one where both ions are determined together and the second after one of them has been masked with a specific complexing agent. The effect of interfering heavy metals such as Cu, Fe, Mn or Zn can be avoided by adding cyanide. The AOAC Official Method 964.01 for determination of acid-soluble... 

Mg in fertilizers is based on such proceedings thereof has been applied on multiple occasions. In milk fermentation, where the samples were dried, calcined in a furnace at 600 °C, the ash was dissolved in 0.03 M HCl, the solution was centrifuged and the supernatant was thus analyzed . The complexometric method for determination of Ca(II) and Mg(II) can be carried out in a single titration with EDTA in alkaline solution, using a Ca-ISE for potentiometric determination of two endpoints. This is accomplished on digitally plotting pCa values measured by the ISE as a function of the volume V of titrant added to the aliquot of analyte the first and second inflection points of the curve mark the Ca(II) and Mg(n) equivalences, respectively. ... 

To determine the amount of calcium in a water sample, e.g. the titration with EDTA (ethylenediaminetetraacetate, C2H4N2(CH2COOH)4) can be used. First of all, NaOH is added to the sample to obtain a pH value of at least 12. Then, a color indicator is admixed and titration with EDTA performed until the color changes. In doing so, all Ca is converted to a Ca-EDTA complex and detected in this form. 

Ca and Mg in water (water hardness) Ca determination Add 2 cm 3 of NaOH solution (0.1 mol dm 3) to 50 cm3 of sample and titrate with EDTA using murexide indicator (table 5.8). Mg determination Destroy murexide colour with 1 cm3 concentrated HQ add 3 cm3 of NH3—NH4C1 buffer and titrate with EDTA using eriochrome black T. 

Conveniently, the TDS content of public water supplies parallels the total electrolyte concentration, so that both the TDS and total electrolyte concentrations can be gauged, at least approximately, by measuring the conductivity of the water 1.00 /iS cm corresponds to 0.65 ppm TDS. Calcium and magnesium contents were traditionally determined by titration with EDTA at pH 10, at which both Ca " " and Mg + axe complexed, and then in a fresh sample at pH 12-13, at which Mg(OH)2 precipitates... 

Figure 13-6 shows pH ranges in which various metal ion indicators (discussed in the next section) are useful for finding end points. The chart also provides a strategy for selective titration of one ion in the presence of another. For example, a solution containing both Fe and Ca could be titrated with EDTA at pH 4. At this pH, Fe is titrated without interference from Ca. ... 

To measure hardness, water is treated with ascorbic acid to reduce Fe to Fe and with cyanide to mask Fe, Cu, and several other minor metal ions. Titration with EDTA at pH 10 in ammonia buffer gives [Ca ] + [Mg ]. [Ca ] can be determined separately if the titration is carried out at pH 13 without ammonia. At this pH, Mg(OH)2 precipitates and is inaccessible to EDTA. 

For the preparation of the Ca(HC03)2 solutions several grams of CaC03 were suspended in 0.5 L water and flushed with gaseous CO2 for about 2 h. In order to remove excess CaC03 the solution was filtered. In addition, the solutions were filtered again before each application. The concentration of the Ca(HC03)2 solutions prepared by this method was approximately 8 mM (determined by titration with EDTA). The pH of this solution was 7.2. 

Fig. 11-L A spectrophotomeiric titration curve of Mg + Ca + Sr with EDTA at pH 10 using Eriochrom Black T as indicator (at 640 nm).

Another means to increase the selectivity is to carry out a preliminary separation of the ion to be titrated if, of course, it is easy to perform. Eor example, Ca +, Ni +, Mg +, and Cu + can be isolated as precipitates of, respectively, oxalate, dimethylglyoximate, ammonium magnesium phosphate, and Cu thiocyanate (see Part V of this book). After dissolution of these precipitates, the liberated metal cation is titrated with EDTA. In some rare cases, the metallic ion may be selectively extracted from the solution into an organic solvent and then determined with EDTA in convenient experimental conditions, for example, after dilution of the organic phase with water. 

It is interesting to notice that the titration with EDTA of Ca + alone is possible in the presence of eriochrome black T, but no sharp endpoint is obtained. A little quantity of the Na2 [MgEDTA] complex must be added to the vessel solution containing Ca + in order for the indication to be possible. The latter complex is by far more stable than the Ca-indicator complex. In these conditions, the Mg + ions are liberated according to the reaction... 

It is easily conceivable that a Ca + and Mg + mixture may be globally titrated in such a way with EDTA. The last edition of the European pharmacopeia prescribed the Ca titration with calcon as the indicator. 

Usability of such miniature galvanic cells equipped with CP-based reference membrane was confirmed experimentally [21]. One of such microcells, with a solid-contact type Ca-sensitive electrode and the PEDOT-SSA reference membrane, was used for end-point detection in the course of calcium titration with EDTA in a borate buffer (pH 9.2). The potential changes were measured against an external Ag/AgCl electrode and potential change for the PEDOT-SSA membrane was negligible during the whole titration. 

Why is magnesium-EDTA chelate added to a magnesium-free water sample before it is to be titrated with EDTA for Ca ... 

Ca" can then titrated with EDTA using calcon indicator ... 

A small amount of material which reacts with the titrating agent and which is itself specifically indicated by an ion-selective electrode is added to the sample solution In this way Ca ions can be titrated with EDTA with the help of a Cu electrode and a trace of Cu ions. Such a titration curve is iQustrated in Fig. 44. Cu forms a more... 

Analyses, (a) Original zinc-ion solution. Dilute 2.00 mL (pipette) to 100 mL in a graduated flask. Pipette 10.0 mL of the diluted solution into a 250 mL conical flask, add ca 90 mL of water, 2 mL of the buffer solution, and sufficient of the solochrome black indicator mixture to impart a pronounced red colour to the solution. Titrate with standard 0.01 M EDTA to a pure blue colour (see Section 10.59). 

Pipette 25 mL barium ion solution (ca 0.01 M) into a 250 mL conical flask and dilute to about 100 mL with de-ionised water. Adjust the pH of the solution to 12 by the addition of 3-6 mL of 1M sodium hydroxide solution the pH must be checked with a pH meter as it must lie between 11.5 and 12.7. Add 50 mg of methyl thymol blue/potassium nitrate mixture [see Section 10.50(C)] and titrate with standard (0.01 M) EDTA solution until the colour changes from blue to grey. 

Into a conical flask, pipette a 50.0 or 100.0 mL aliquot of the solution and adjust the pH to 1-2 with aqueous ammonia solution (use pH test-paper). Add five drops of xylenol orange indicator and titrate with additional 0.05 M EDTA until the colour changes sharply from red to yellow. This gives the bismuth content. Record the total (combined) volume of EDTA solution used. Now add small amounts of hexamine (ca 5g) until an intense red-violet coloration persists, and titrate with the standard EDTA to a yellow end point the further consumption of EDTA corresponds to the lead-plus-cadmium content. 

Discussion. Salicylic acid and iron(III) ions form a deep-coloured complex with a maximum absorption at about 525 nm this complex is used as the basis for the photometric titration of iron(III) ion with standard EDTA solution. At a pH of ca 2.4 the EDTA-iron complex is much more stable (higher stability constant) than the iron-salicylic acid complex. In the titration of an iron-salicylic acid solution with EDTA the iron-salicylic acid colour will therefore gradually disappear as the end point is approached. The spectrophotometric end point at 525 nm is very sharp. 

PVC (200 mg) was dissolved in 20 mL THF and precipitated with 50 mL EtOH. Several drops of 0.1 % pyrocatechol violet solution were added to the heated filtrate until a blue colour appeared. This solution was titrated with 0.001 M EDTA until the change via green to yellow. In the presence of Mg, Ca, and Zn, Eriochrome Black was added before titration. 

If the analyte metal ion forms a stable EDTA complex rapidly, and an end point can be readily detected, a direct titration procedure may be employed. More than thirty metal ions may be so determined. Where the analyte is partially precipitated under the reaction conditions thereby leading to a slow reaction, or where a suitable indicator cannot be found, back titration procedures are used. A measured excess of EDTA is added and the unreacted EDTA titrated with a standard magnesium or calcium solution. Provided the analyte complex is stronger than the Ca-EDTA or Mg-EDTA complex a satisfactory end point may be obtained with eriochrome black T as indicator. An alternative procedure, where end points are difficult to observe, is to use a displacement reaction. In this case, a measured excess of EDTA is added as its zinc or magnesium complex. Provided the analyte complex is the stronger, the analyte will displace the zinc or magnesium. 

The fully reduced state of CCP is probably of no physiological significance. However, the visible region spectrum of the fully reduced enzyme is very sensitive to the presence or absence of bound Ca + ions. In the absence of Ca + ions the a-band maximum of the reduced enzyme, recorded during the course of the redox titrations described earlier, is at 551 nm with a shoulder at 557 nm. In contrast, in fully reduced Ca +-loaded enzyme the maximum is at 557 nm with a shoulder 551 nm (52). These spectra should be compared with those of the fully reduced Psew-domonas CCP in its inactive and active forms, respectively, which show similar differences (81). Further similarities exist between the X-band EPR spectra of the active CCP from P. aeruginosa in the MV state and that of the Ca +-loaded CCP from P. denitrificans and, moreover, the X-band EPR spectrum of MV P denitrificans CCP that had previously been treated with EDTA (Table I). 

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