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C_\textrm{EDTA}&=\dfrac{M_\textrm{EDTA}V_\textrm{EDTA}-M_\textrm{Cd}V_\textrm{Cd}}{V_\textrm{Cd}+V_\textrm{EDTA}}\\ CJ OJ QJ ^J aJ hLS CJ OJ QJ ^J aJ h, h% CJ OJ QJ ^J aJ h- CJ OJ QJ ^J aJ t v 0 6 F H J L N ` b B C k l m n o r #hH hH >*CJ OJ QJ ^J aJ hH CJ OJ QJ ^J aJ hk hH CJ OJ QJ ^J aJ h% CJ OJ QJ ^J aJ hLS h% CJ OJ QJ ^J aJ hLS CJ OJ QJ ^J aJ h, h% CJ OJ QJ ^J aJ hp CJ OJ QJ ^J aJ h, h% CJ OJ QJ ^J aJ $ 1 4  |n||||]]||n| h, h% CJ OJ QJ ^J aJ hLS CJ OJ QJ ^J aJ hp CJ OJ QJ ^J aJ h, h% CJ OJ QJ ^J aJ hk hk CJ OJ QJ ^J aJ h% CJ OJ QJ ^J aJ #h hH CJ H*OJ QJ ^J aJ hH CJ OJ QJ ^J aJ #hH hH >*CJ OJ QJ ^J aJ &h hH >*CJ H*OJ QJ ^J aJ !o | } h% 5>*CJ OJ QJ ^J aJ mHsH +h, h, 5CJ OJ QJ ^J aJ mHsH { ~ " : kWI8 h, h% CJ OJ QJ ^J aJ hp CJ OJ QJ ^J aJ &h, h% 5CJ OJ QJ \^J aJ &hk hLS 5CJ OJ QJ \^J aJ &hLS h% 5CJ OJ QJ \^J aJ hlx% 5CJ OJ QJ \^J aJ hs CJ OJ QJ ^J aJ &h, h, 6CJ OJ QJ ]^J aJ )hs h% 6CJ H*OJ QJ ]^J aJ hs 6CJ OJ QJ ]^J aJ &h, h% 6CJ OJ QJ ]^J aJ : $ ( * , . h, 5>*CJ H*OJ QJ ^J aJ mHsH.h The description here is based on Method 2340C as published in Standard Methods for the Examination of Water and Wastewater, 20th Ed., American Public Health Association: Washington, D. C., 1998. For example, after adding 5.0 mL of EDTA, the total concentration of Cd2+ is, \[\begin{align} Problem 9.42 from the end of chapter problems asks you to verify the values in Table 9.10 by deriving an equation for Y4-. Other common spectrophotometric titration curves are shown in Figures 9.31b-f. It determines the constituent of calcium and magnesium in the liquids such as sea water, milk etc. You will work in partners as determined by which unknown was chosen. In a titration to establish the concentration of a metal ion, the EDTA that is added combines quantitatively with the cation to form the complex. Total hardness is a measure by which the amount of calcium and magnesium in a given water sample is assessed. This can be done by raising the pH to 12, which precipitates the magnesium as its hydroxide: Mg2+ + 2OH- Mg(OH) 2 &=6.25\times10^{-4}\textrm{ M} Hardness is mainly the combined constituent of both magnesium and calcium. The end point is determined using p-dimethylaminobenzalrhodamine as an indicator, with the solution turning from a yellow to a salmon color in the presence of excess Ag+. In this experiment you will standardize a solution of EDTA by titration against a standard This reagent can forms a stable complex with the alkaline earth metal like calcium ion and magnesium ion in alkaline condition pH above 9.0. Thus, when the titration reaches 110% of the equivalence point volume, pCd is logKf 1. Titration . @ A udRAdR3%hp CJ OJ QJ ^J aJ hLS CJ OJ QJ ^J aJ h, h% CJ OJ QJ ^J aJ #hlx% h% CJ H*OJ QJ ^J aJ h, h% CJ OJ QJ ^J aJ &hk hLS 5CJ OJ QJ \^J aJ h% 5CJ OJ QJ \^J aJ h 5CJ OJ QJ \^J aJ &h, h% 5CJ OJ QJ \^J aJ (hk h% CJ OJ QJ ^J aJ mHsH (hlx% h% CJ OJ QJ ^J aJ mHsH +hlx% hlx% 5CJ OJ QJ ^J aJ mHsH A D ` h k o r { y z " # 3 4 I J V { yk hlx% CJ OJ QJ ^J aJ ,h(5 h% 5B* Calcium and Magnesium ion concentration determination with EDTA titration 56,512 views Dec 12, 2016 451 Dislike Share Save Missy G. 150 subscribers CHEM 249 Extra credit by Heydi Dutan and. Calculations. The first four values are for the carboxylic acid protons and the last two values are for the ammonium protons. Click n=CV button above EDTA4+ in the input frame, enter volume and concentration of the titrant used. The equivalence point of a complexation titration occurs when we react stoichiometrically equivalent amounts of titrand and titrant. At the end point the color changes from wine red to blue. This provides some control over an indicators titration error because we can adjust the strength of a metalindicator complex by adjusted the pH at which we carry out the titration. 1ml of 0.1N potassium permanganate is equivalent to 0.2 mg of calcium Therefore, X3 ml of' Y' N potassium permanganate is equivalent to. By direct titration, 5 ml. To maintain a constant pH during a complexation titration we usually add a buffering agent. ! Lets use the titration of 50.0 mL of 5.00103 M Cd2+ with 0.0100 M EDTA in the presence of 0.0100 M NH3 to illustrate our approach. a pCd of 15.32. 0000020364 00000 n The solution is warmed to 40 degrees C and titrated against EDTA taken in the burette. 0000021034 00000 n Perform a blank determination and make any necessary correction. About Press Copyright Contact us Creators Advertise Developers Terms Privacy Policy & Safety How YouTube works Test new features NFL Sunday Ticket Press Copyright . Solving equation 9.13 for [Cd2+] and substituting into equation 9.12 gives, \[K_\textrm f' =K_\textrm f \times \alpha_{\textrm Y^{4-}} = \dfrac{[\mathrm{CdY^{2-}}]}{\alpha_\mathrm{Cd^{2+}}C_\textrm{Cd}C_\textrm{EDTA}}\], Because the concentration of NH3 in a buffer is essentially constant, we can rewrite this equation, \[K_\textrm f''=K_\textrm f\times\alpha_\mathrm{Y^{4-}}\times\alpha_\mathrm{Cd^{2+}}=\dfrac{[\mathrm{CdY^{2-}}]}{C_\textrm{Cd}C_\textrm{EDTA}}\tag{9.14}\]. Titrating with EDTA using murexide or Eriochrome Blue Black R as the indicator gives the concentration of Ca2+. Report the purity of the sample as %w/w NaCN. Because the pH is 10, some of the EDTA is present in forms other than Y4. Formation constants for other metalEDTA complexes are found in Table E4. The second titration uses, \[\mathrm{\dfrac{0.05831\;mol\;EDTA}{L}\times0.03543\;L\;EDTA=2.066\times10^{-3}\;mol\;EDTA}\]. EDTA (L) Molarity. ^208u4-&2`jU" JF`"Py~}L5@X2.cXb43{b,cbk X$ \end{align}\], \[\begin{align} Analysis of an Epsom Salt Sample Example 2 A sample of Epsom Salt of mass0.7567 g was dissolved uniformly in distilled water in a250 mL volumetric flask. Answer Mol arity EDTA (m ol / L) = Volume Zinc ( L) Mol rity m l / 1 mol EDTA 1 mol Zinc 1 . Water hardness is determined by the total concentration of magnesium and calcium. ! The blue line shows the complete titration curve. Furthermore, lets assume that the titrand is buffered to a pH of 10 with a buffer that is 0.0100 M in NH3. Note that the titration curves y-axis is not the actual absorbance, A, but a corrected absorbance, Acorr, \[A_\textrm{corr}=A\times\dfrac{V_\textrm{EDTA}+V_\textrm{Cu}}{V_\textrm{Cu}}\]. A red to blue end point is possible if we maintain the titrands pH in the range 8.511. Before adding EDTA, the mass balance on Cd2+, CCd, is, and the fraction of uncomplexed Cd2+, Cd2+, is, \[\alpha_{\textrm{Cd}^{2+}}=\dfrac{[\mathrm{Cd^{2+}}]}{C_\textrm{Cd}}\tag{9.13}\]. &=\dfrac{(5.00\times10^{-3}\textrm{ M})(\textrm{50.0 mL})}{\textrm{50.0 mL + 25.0 mL}}=3.33\times10^{-3}\textrm{ M} Take a sample volume of 20ml (V ml). Read mass of magnesium in the titrated sample in the output frame. 0000000016 00000 n (3) Tabulate and plot the emission intensity vs. sodium concentration for the NaCl standards and derive the calibration equation for the two sets of measurements (both burner orientations). Because Ca2+ forms a stronger complex with EDTA, it displaces Mg2+ from the Mg2+EDTA complex, freeing the Mg2+ to bind with the indicator. Complexation titrations, however, are more selective. The titration is done with 0.1 mol/l AgNO3 solution to an equivalence point. At the beginning of the titration the absorbance is at a maximum. Calculation of EDTA titration results is always easy, as EDTA reacts with all metal ions in 1:1 ratio: That means number of moles of magnesium is exactly that of number of moles of EDTA used. Using the volumes of solutions used, their determined molarity, you will be able to calculate the amount of magnesium in the given sample of water. In this case the interference is the possible precipitation of CaCO3 at a pH of 10. A variety of methods are available for locating the end point, including indicators and sensors that respond to a change in the solution conditions. Here the concentration of Cd2+ is controlled by the dissociation of the Cd2+EDTA complex. PAGE \* MERGEFORMAT 1 U U U U U U U U U. To calculate magnesium solution concentration use EBAS - stoichiometry calculator. Hardness of water is a measure of its capacity to precipitate soap, and is caused by the presence of divalent cations of mainly Calcium and Magnesium. Why does the procedure specify that the titration take no longer than 5 minutes? Even if a suitable indicator does not exist, it is often possible to complete an EDTA titration by introducing a small amount of a secondary metalEDTA complex, if the secondary metal ion forms a stronger complex with the indicator and a weaker complex with EDTA than the analyte. %Srr~81@ n0/Mm`:5 A)r=AKVvY Ri9~Uvhug BAp$eK,v$R!36e8"@` EBAS - equation balancer & stoichiometry calculator, Operating systems: XP, Vista, 7, 8, 10, 11, BPP Marcin Borkowskiul. %PDF-1.4 % Next, we draw our axes, placing pCd on the y-axis and the titrants volume on the x-axis. Repeat the titration twice. Finally, we complete our sketch by drawing a smooth curve that connects the three straight-line segments (Figure 9.29e). After filtering and rinsing the precipitate, it is dissolved in 25.00 mL of 0.02011 M EDTA. This is how you can perform an estimation of magnesium using edta. A complexometric titration method is proposed to determine magnesium oxide in flyash blended cement. More than 95% of calcium in our body can be found in bones and teeth. 0000001334 00000 n Determination of Calcium and Magnesium in Water . 2) You've got some . 0000034266 00000 n The most widely used of these new ligandsethylenediaminetetraacetic acid, or EDTAforms strong 1:1 complexes with many metal ions. The solid lines are equivalent to a step on a conventional ladder diagram, indicating conditions where two (or three) species are equal in concentration. As shown in Table 9.11, the conditional formation constant for CdY2 becomes smaller and the complex becomes less stable at more acidic pHs. 0 A 0.1557-g sample is dissolved in water, any sulfate present is precipitated as BaSO4 by adding Ba(NO3)2. <<7daf3a9c17b9c14e9b00eea5d2c7d2c8>]>> 0000031526 00000 n At the equivalence point we know that moles EDTA = moles Cd2 + MEDTA VEDTA = MCd VCd Substituting in known values, we find that it requires Veq = VEDTA = MCdVCd MEDTA = (5.00 10 3 M)(50.0 mL) 0.0100 M = 25.0 mL Chloride is determined by titrating with Hg(NO3)2, forming HgCl2(aq). Use the standard EDTA solution to titrate the hard water. The resulting metalligand complex, in which EDTA forms a cage-like structure around the metal ion (Figure 9.26b), is very stable. Figure 9.33 shows the titration curve for a 50-mL solution of 103 M Mg2+ with 102 M EDTA at pHs of 9, 10, and 11. Correcting the absorbance for the titrands dilution ensures that the spectrophotometric titration curve consists of linear segments that we can extrapolate to find the end point. to the EDTA titration method for the determination of total hardness, based on your past experience with the ETDA method (e.g., in CH 321.) teacher harriet voice shawne jackson; least stressful physician assistant specialties; grandma's marathon elevation gain; describe key elements of partnership working with external organisations; EDTA can form four or six coordination bonds with a metal ion. Solution for Calculate the % Copper in the alloy using the average titration vallue. 0000000016 00000 n h`. A 0.50 g of sample was heated with hydrochloric acid for 10 min. Background Calcium is an important element for our body. 3. the solutions used in here are diluted. The titration can be carried out with samples with chloride contents of a few ppm - 100%, but the amount of sample has to be adjusted. B = mg CaCO3 equivalent to 1 ml EDTA Titrant. In section 9B we learned that an acidbase titration curve shows how the titrands pH changes as we add titrant. Protocol B: Determination of Aluminum Content Alone Pipet a 10.00 ml aliquot of the antacid sample solution into a 125 ml. (% w / w) = Volume. The resulting spectrophotometric titration curve is shown in Figure 9.31a. 4. |" " " " " " " # # # # # >$ {l{]K=/=h0Z CJ OJ QJ ^J aJ h)v CJ OJ QJ ^J aJ #hk hk 5CJ OJ QJ ^J aJ h 5CJ OJ QJ ^J aJ h)v 5CJ OJ QJ ^J aJ hL 5CJ OJ QJ ^J aJ hk CJ OJ QJ ^J aJ hH CJ OJ QJ ^J aJ hlx% CJ OJ QJ ^J aJ hlx% hlx% CJ OJ QJ ^J aJ hlx% hH CJ OJ QJ ^J aJ (h- hH CJ OJ QJ ^J aJ mHsH (hk hk CJ OJ QJ ^J aJ mHsH>$ ?$ % % P OQ fQ mQ nQ R yS zS T T T U U U U U U U U U U !U 8U 9U :U ;U =U ?U @U xj j h7 UmH nH u h? The determination of the Calcium and Magnesium next together in water is done by titration with the sodium salt of ethylenediaminetetraethanoic acid (EDTA) at pH 8 9, the de- tection is carried out with a Ca electrode. Report the samples hardness as mg CaCO3/L. [\mathrm{CdY^{2-}}]&=\dfrac{\textrm{initial moles Cd}^{2+}}{\textrm{total volume}}=\dfrac{M_\textrm{Cd}V_\textrm{Cd}}{V_\textrm{Cd}+V_\textrm{EDTA}}\\ MgSO4 Mg2++SO42- Experimental: With respect to #"magnesium carbonate"#, this is #17 . The amount of EDTA reacting with Cu is, \[\mathrm{\dfrac{0.06316\;mol\;Cu^{2+}}{L}\times0.00621\;L\;Cu^{2+}\times\dfrac{1\;mol\;EDTA}{mol\;Cu^{2+}}=3.92\times10^{-4}\;mol\;EDTA}\]. The availability of a ligand that gives a single, easily identified end point made complexation titrimetry a practical analytical method. Table 2 Determination of Total Hardness of Water Trials Volume of Sample (mL) Nt. At a pH of 3 EDTA reacts only with Ni2+. Prepare a standard solution of magnesium sulfate and titrate it against the given EDTA solution using Eriochrome Black T as the indicator. Buffer . There is a second method for calculating [Cd2+] after the equivalence point. Pipette 10 mL of the sample solution into a conical flask. to give a conditional formation constant, Kf, that accounts for both pH and the auxiliary complexing agents concentration. 0000023545 00000 n Calmagite is used as an indicator. The initial solution is a greenish blue, and the titration is carried out to a purple end point. Method C, the EDTA titration method, measures the calcium and magnesium ions and may be applied with appro-priate modication to any kind of water. In the initial stages of the titration magnesium ions are displaced from the EDTA complex by calcium ions and are . 0000002393 00000 n Our derivation here is general and applies to any complexation titration using EDTA as a titrant. In addition magnesium forms a complex with the dye Eriochrome Black T. We will also need indicator - either in the form of solution, or ground with NaCl - 100mg of indicator plus 20g of analytical grade NaCl. 1 Answer anor277 . Both analytes react with EDTA, but their conditional formation constants differ significantly. Compare your sketches to the calculated titration curves from Practice Exercise 9.12. 0000022320 00000 n lab report 6 determination of water hardnessdream about someone faking their death. The concentration of Cd2+, therefore, is determined by the dissociation of the CdY2 complex. The pH affects a complexometric EDTA titration in several ways and must be carefully controlled. Repeat titrations for concordant values. Calcium can be precipitated as carbonate or oxalate, although presence of oxalates may make end point detection difficult. A 0.4482-g sample of impure NaCN is titrated with 0.1018 M AgNO3, requiring 39.68 mL to reach the end point. If one of the buffers components is a ligand that binds Cd2+, then EDTA must compete with the ligand for Cd2+. Next, we draw a straight line through each pair of points, extending the line through the vertical line representing the equivalence points volume (Figure 9.29d). EDTA, which is shown in Figure 9.26a in its fully deprotonated form, is a Lewis acid with six binding sitesfour negatively charged carboxylate groups and two tertiary amino groupsthat can donate six pairs of electrons to a metal ion. EDTA (mol / L) 1 mol Calcium. (mg) =Volume. concentration and the tap water had a relatively normal level of magnesium in comparison. An analysis done on a series of samples with known concentrations is utilized to build a calibration curve. Add 1 mL of ammonia buffer to bring the pH to 100.1. For 0.01M titrant and assuming 50mL burette, aliquot taken for titration should contain about 0.35-0.45 millimoles of magnesium (8.5-11mg). 0000014114 00000 n 0000021941 00000 n The quantitative relationship between the titrand and the titrant is determined by the stoichiometry of the titration reaction. This can be analysed by complexometric titration. For example, an NH4+/NH3 buffer includes NH3, which forms several stable Cd2+NH3 complexes. Let us explain the principle behind calculation of hardness. The reaction between EDTA and all metal ions is 1 mol to 1 mol.Calculate the molarity of the EDTA solution. startxref Step 4: Calculate pM at the equivalence point using the conditional formation constant. seems!to!proceed!slowly!near!the!equivalence!point,!after!each!addition!of! Why is the sample buffered to a pH of 10? Determination of Hardness: Hardness is expressed as mg/L CaCO 3. When the reaction is complete all the magnesium ions would have been complexed with EDTA and the free indicator would impart a blue color to the solution. Each mole of Hg2+ reacts with 2 moles of Cl; thus, \[\mathrm{\dfrac{0.0516\;mol\;Hg(NO_3)_2}{L}\times0.00618\;L\;Hg(NO_3)_2\times\dfrac{2\;mol\;Cl^-}{mol\;Hg(NO_3)_2}\times\dfrac{35.453\;g\;Cl^-}{mol\;Cl^-}=0.0226\;g\;Cl^-}\], are in the sample. Add a pinch of Eriochrome BlackT ground with sodium chloride (100mg of indicator plus 20g of analytical grade NaCl). Titrate with EDTA solution till the color changes to blue. h% CJ OJ QJ ^J aJ h`. This may be difficult if the solution is already colored. Standardization of EDTA: 20 mL of the standard magnesium sulfate solution is pipetted out into a 250 mL Erlenmeyer flask and diluted to 100 mL . In the process of titration, both the volumetric addition of titra For example, calmagite gives poor end points when titrating Ca2+ with EDTA. 0000008621 00000 n The experimental approach is essentially identical to that described earlier for an acidbase titration, to which you may refer. The concentration of Cl in a 100.0-mL sample of water from a freshwater aquifer was tested for the encroachment of sea water by titrating with 0.0516 M Hg(NO3)2. Just like during determination of magnesium all metals other than alkali metals can interfere and should be removed prior to titration. \[\textrm{MIn}^{n-}+\textrm Y^{4-}\rightarrow\textrm{MY}^{2-}+\textrm{In}^{m-}\]. dh 7$ 8$ H$ ^gd Dissolve the salt completely using distilled or de-ionized water. Finally, complex titrations involving multiple analytes or back titrations are possible. First, we calculate the concentrations of CdY2 and of unreacted EDTA. Titration is one of the common method used in laboratories which determines the unknown concentration of an analyte that has been identified. To illustrate the formation of a metalEDTA complex, lets consider the reaction between Cd2+ and EDTA, \[\mathrm{Cd^{2+}}(aq)+\mathrm{Y^{4-}}(aq)\rightleftharpoons \mathrm{CdY^{2-}}(aq)\tag{9.9}\], where Y4 is a shorthand notation for the fully deprotonated form of EDTA shown in Figure 9.26a. 6ADIDnu1cGM?froF%a,;on_Qw!"eEA#z@$\Xx0f 80BUGc77 b`Y]TkEZt0Yu}5A\vm5Fvh5A/VbgvZd In this study The highest mean level of calci um was obtained in melon (22 0 mg/100g) followed by water leaf (173 mg/100g), then white beans (152 mg/100g . Figure 9.29b shows the pCd after adding 5.00 mL and 10.0 mL of EDTA. From Table 9.10 and Table 9.11 we find that Y4 is 0.35 at a pH of 10, and that Cd2+ is 0.0881 when the concentration of NH3 is 0.0100 M. Using these values, the conditional formation constant is, \[K_\textrm f''=K_\textrm f \times \alpha_\mathrm{Y^{4-}}\times\alpha_\mathrm{Cd^{2+}}=(2.9\times10^{16})(0.37)(0.0881)=9.5\times10^{14}\], Because Kf is so large, we can treat the titration reaction, \[\textrm{Cd}^{2+}(aq)+\textrm Y^{4-}(aq)\rightarrow \textrm{CdY}^{2-}(aq)\]. Adding a small amount of Mg2+EDTA to the titrand gives a sharper end point. (b) Diagram showing the relationship between the concentration of Mg2+ (as pMg) and the indicators color. Adding a small amount of Mg2+EDTA to the buffer ensures that the titrand includes at least some Mg2+. Both solutions are buffered to a pH of 10.0 using a 0.100M ammonia buffer. Indicator. Eriochrome Black-T(EBT) is the metal ion indicator used in the determination of hardness by complexometric titration with EDTA. 2. If the sample does not contain any Mg2+ as a source of hardness, then the titrations end point is poorly defined, leading to inaccurate and imprecise results. The earliest examples of metalligand complexation titrations are Liebigs determinations, in the 1850s, of cyanide and chloride using, respectively, Ag+ and Hg2+ as the titrant. Figure 9.32 End point for the titration of hardness with EDTA using calmagite as an indicator; the indicator is: (a) red prior to the end point due to the presence of the Mg2+indicator complex; (b) purple at the titrations end point; and (c) blue after the end point due to the presence of uncomplexed indicator. The amount of calcium present in the given sample can be calculated by using the equation. If at least one species in a complexation titration absorbs electromagnetic radiation, we can identify the end point by monitoring the titrands absorbance at a carefully selected wavelength. This means that the same concentration of eluent is always pumped through the column. U! Step 2: Calculate the volume of EDTA needed to reach the equivalence point. Determination of Hardness of Water and Wastewater. CJ H*OJ QJ ^J aJ h`. Cyanide is determined at concentrations greater than 1 mg/L by making the sample alkaline with NaOH and titrating with a standard solution of AgNO3, forming the soluble Ag(CN)2 complex. To evaluate the titration curve, therefore, we first need to calculate the conditional formation constant for CdY2. 0000000676 00000 n The sample, therefore, contains 4.58104 mol of Cr. in triplicates using the method of EDTA titration. In this section we will learn how to calculate a titration curve using the equilibrium calculations from Chapter 6. This point coincides closely to the endpoint of the titration, which can be identified using an . For example, we can identify the end point for a titration of Cu2+ with EDTA, in the presence of NH3 by monitoring the titrands absorbance at a wavelength of 745 nm, where the Cu(NH3)42+ complex absorbs strongly. ! At any pH a mass balance on EDTA requires that its total concentration equal the combined concentrations of each of its forms. As is the case with acidbase titrations, we estimate the equivalence point of a complexation titration using an experimental end point. Figure 9.31 Examples of spectrophotometric titration curves: (a) only the titrand absorbs; (b) only the titrant absorbs; (c) only the product of the titration reaction absorbs; (d) both the titrand and the titrant absorb; (e) both the titration reactions product and the titrant absorb; (f) only the indicator absorbs. The reaction between Mg2+ ions and EDTA can be represented like this. EDTA (L) Molarity. The other three methods consisted of direct titrations (d) of mangesium with EDTA to the EBT endpoint after calcium had been removed.