determination of magnesium by edta titration calculations

0000000676 00000 n %%EOF 0000028404 00000 n Menu. Titration is one of the common method used in laboratories which determines the unknown concentration of an analyte that has been identified. The Titration After the magnesium ions have been precipitated out of the hard water by the addition of NaOH (aq) to form white Mg(OH) 2(s), the remaining Ca 2+ ions in solution are titrated with EDTA solution.. This dye-stuff tends to polymerize in strongly acidic solutions to a red brown product, and hence the indicator is generally used in EDTA titration with solutions having pH greater than 6.5. Determination of Total hardness Repeat the above titration method for sample hard water instead of standard hard water. Magnesium can be easily determined by EDTA titration in the pH10 against Eriochrome BlackT. If the solution initially contains also different metal ions, they should be removed or masked, as EDTA react easily with most cations (with the exception of alkali metals). startxref Repeat titrations for concordant values. 0000041216 00000 n When the reaction between the analyte and titrant is complete, you can observe a change in the color of the solution or pH changes. See Figure 9.11 for an example. A spectrophotometric titration is a particularly useful approach for analyzing a mixture of analytes. This is how you can perform an estimation of magnesium using edta. 0000002997 00000 n 0000000961 00000 n which is the end point. The concentration of Ca2+ ions is usually expressed as ppm CaCO 3 in the water sample. 0000038759 00000 n This can be analysed by complexometric titration. The operational definition of water hardness is the total concentration of cations in a sample capable of forming insoluble complexes with soap. Suppose we need to analyze a mixture of Ni2+ and Ca2+. Thus, by measuring only magnesium concentration in the 2.1 The magnesium EDTA exchanges magnesium on an equivalent basis for any calcium and/or other cations to form a more stable EDTA chelate than magnesium. B = mg CaCO3 equivalent to 1 ml EDTA Titrant. Magnesium ions form a less stable EDTA complex compared to calcium ions but a more stable indicator complex hence a small amount of Mg2+ or Mg-EDTA complex is added to the reaction mixture during the titration of Ca2+ with EDTA. 0 Volume required to neutralise EDTA. Introduction: Hardness in water is due to the presence of dissolved salts of calcium and magnesium. 0000000832 00000 n Table 9.14 provides examples of metallochromic indicators and the metal ions and pH conditions for which they are useful. 0000016796 00000 n 0000000016 00000 n After the equivalence point, EDTA is in excess and the concentration of Cd2+ is determined by the dissociation of the CdY2 complex. Both solutions are buffered to a pH of 10.0 using a 0.100M ammonia buffer. The reason we can use pH to provide selectivity is shown in Figure 9.34a. The indicator, Inm, is added to the titrands solution where it forms a stable complex with the metal ion, MInn. 23 0 obj<>stream Aim: Determine the total hardness of given water samples. Legal. \[K_\textrm f''=\dfrac{[\mathrm{CdY^{2-}}]}{C_\textrm{Cd}C_\textrm{EDTA}}=\dfrac{3.33\times10^{-3}-x}{(x)(x)}= 9.5\times10^{14}\], \[x=C_\textrm{Cd}=1.9\times10^{-9}\textrm{ M}\]. 0000011407 00000 n In addition to its properties as a ligand, EDTA is also a weak acid. Titrating with 0.05831 M EDTA required 35.43 mL to reach the murexide end point. 6ADIDnu1cGM?froF%a,;on_Qw!"eEA#z@$\Xx0f 80BUGc77 b`Y]TkEZt0Yu}5A\vm5Fvh5A/VbgvZd We can account for the effect of an auxiliary complexing agent, such as NH3, in the same way we accounted for the effect of pH. The third titration uses, \[\mathrm{\dfrac{0.05831\;mol\;EDTA}{L}\times0.05000\;L\;EDTA=2.916\times10^{-3}\;mol\;EDTA}\], of which 1.524103 mol are used to titrate Ni and 5.42104 mol are used to titrate Fe. Figure 9.29 Illustrations showing the steps in sketching an approximate titration curve for the titration of 50.0 mL of 5.00 103 M Cd2+ with 0.0100 M EDTA in the presence of 0.0100 M NH3: (a) locating the equivalence point volume; (b) plotting two points before the equivalence point; (c) plotting two points after the equivalence point; (d) preliminary approximation of titration curve using straight-lines; (e) final approximation of titration curve using a smooth curve; (f) comparison of approximate titration curve (solid black line) and exact titration curve (dashed red line). 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). Given the Mg2+: EDTA ratio of 1 : 1, calculate the concentration of your EDTA solution. teacher harriet voice shawne jackson; least stressful physician assistant specialties; grandma's marathon elevation gain; describe key elements of partnership working with external organisations; h`. The displacement by EDTA of Mg2+ from the Mg2+indicator complex signals the titrations end point. EDTA solution. Note that after the equivalence point, the titrands solution is a metalligand complexation buffer, with pCd determined by CEDTA and [CdY2]. Figure 9.29c shows the third step in our sketch. &=\dfrac{(5.00\times10^{-3}\textrm{ M})(\textrm{50.0 mL}) - (\textrm{0.0100 M})(\textrm{5.0 mL})}{\textrm{50.0 mL + 5.0 mL}}=3.64\times10^{-3}\textrm{ M} The red points correspond to the data in Table 9.13. One way to calculate the result is shown: Mass of. Click Use button. Calcium is determined at pH 12 where magnesium is quantitatively precipitated as the hydroxide and will not react with EDTA. If MInn and Inm have different colors, then the change in color signals the end point. The same unknown which was titrated will be analyzed by IC. \end{align}\], \[\begin{align} In an acid-base titration, the titrant is a strong base or a strong acid, and the analyte is an acid or a base, respectively. Figure 9.31 Examples of spectrophotometric titration curves: (a) only the titrand absorbs; (b) only the titrant absorbs; (c) only the product of the titration reaction absorbs; (d) both the titrand and the titrant absorb; (e) both the titration reactions product and the titrant absorb; (f) only the indicator absorbs. last modified on October 27 2022, 21:28:28. This may be difficult if the solution is already colored. 0000014114 00000 n The ladder diagram defines pMg values where MgIn and HIn are predominate species. Other metalligand complexes, such as CdI42, are not analytically useful because they form a series of metalligand complexes (CdI+, CdI2(aq), CdI3 and CdI42) that produce a sequence of poorly defined end points. If the metalindicator complex is too weak, however, the end point occurs before we reach the equivalence point. The titration is performed by adding a standard solution of EDTA to the sample containing the Ca. If preparation of such sample is difficult, we can use different EDTA concentration. \end{align}\], Substituting into equation 9.14 and solving for [Cd2+] gives, \[\dfrac{[\mathrm{CdY^{2-}}]}{C_\textrm{Cd}C_\textrm{EDTA}} = \dfrac{3.13\times10^{-3}\textrm{ M}}{C_\textrm{Cd}(6.25\times10^{-4}\textrm{ M})} = 9.5\times10^{14}\], \[C_\textrm{Cd}=5.4\times10^{-15}\textrm{ M}\], \[[\mathrm{Cd^{2+}}] = \alpha_\mathrm{Cd^{2+}} \times C_\textrm{Cd} = (0.0881)(5.4\times10^{-15}\textrm{ M}) = 4.8\times10^{-16}\textrm{ M}\]. 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. Record the volume used (as V.). A comparison of our sketch to the exact titration curve (Figure 9.29f) shows that they are in close agreement. In the process of titration, both the volumetric addition of titra 8. After the equilibrium point we know the equilibrium concentrations of CdY2- and EDTA. Titration . Prepare a 0.05 M solution of the disodium salt. T! Background Calcium is an important element for our body. Report the samples hardness as mg CaCO3/L. C_\textrm{EDTA}&=\dfrac{M_\textrm{EDTA}V_\textrm{EDTA}-M_\textrm{Cd}V_\textrm{Cd}}{V_\textrm{Cd}+V_\textrm{EDTA}}\\ Elution of the compounds of interest is then done using a weekly acidic solution. Because not all the unreacted Cd2+ is freesome is complexed with NH3we must account for the presence of NH3. At any pH a mass balance on EDTA requires that its total concentration equal the combined concentrations of each of its forms. ! In the section we review the general application of complexation titrimetry with an emphasis on applications from the analysis of water and wastewater. Let the burette reading of EDTA be V 3 ml. To correct the formation constant for EDTAs acidbase properties we need to calculate the fraction, Y4, of EDTA present as Y4. 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. (% w / w) = Volume. The concentration of a solution of EDTA was determined by standardizing against a solution of Ca2+ prepared using a primary standard of CaCO3. Calculate the Aluminum hydroxide and Magnesium hydroxide content in grams in the total diluted sample. Recall that an acidbase titration curve for a diprotic weak acid has a single end point if its two Ka values are not sufficiently different. If one of the buffers components is a ligand that binds Cd2+, then EDTA must compete with the ligand for Cd2+. 0000001090 00000 n Protocol B: Determination of Aluminum Content Alone Pipet a 10.00 ml aliquot of the antacid sample solution into a 125 ml. 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. (Assume the moles of EDTA are equal to the moles of MgCO3) Chemistry Reactions in Solution Titration Calculations. About Press Copyright Contact us Creators Advertise Developers Terms Privacy Policy & Safety How YouTube works Test new features NFL Sunday Ticket Press Copyright . Because EDTA has many forms, when we prepare a solution of EDTA we know it total concentration, CEDTA, not the concentration of a specific form, such as Y4. 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. Add 12 drops of indicator and titrate with a standard solution of EDTA until the red-to-blue end point is reached (Figure 9.32). Table 9.12 provides values of M2+ for several metal ion when NH3 is the complexing agent. The first method is calculation based method and the second method is titration method using EDTA. Most indicators for complexation titrations are organic dyesknown as metallochromic indicatorsthat form stable complexes with metal ions. For the purposes of this lab an isocratic gradient is used. To prevent an interference the pH is adjusted to 1213, precipitating Mg2+ as Mg(OH)2. 0 endstream endobj 267 0 obj <>/Filter/FlateDecode/Index[82 161]/Length 27/Size 243/Type/XRef/W[1 1 1]>>stream Finally, we can use the third titration to determine the amount of Cr in the alloy. Figure 9.27 shows a ladder diagram for EDTA. 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 Calcium. seems!to!proceed!slowly!near!the!equivalence!point,!after!each!addition!of! In the determination of water hardness, ethylene-diaminetetraacetic acid (EDTA) is used as the titrant that complexes Ca2+ and Mg2+ ions. This is the same example that we used in developing the calculations for a complexation titration curve. 0000024745 00000 n As shown in the following example, we can easily extended this calculation to complexation reactions using other titrants. For the titration of Mg2+, one must buffer the solution to a pH of 10 so that complex formation will be quantitative. Having determined the moles of Ni, Fe, and Cr in a 50.00-mL portion of the dissolved alloy, we can calculate the %w/w of each analyte in the alloy. 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. Determination of Hardness: Hardness is expressed as mg/L CaCO 3. calcium and magnesium by complexometric titration with EDTA in the presence of metallo-chromic indicators Calcon or Murexide for Ca 2+ and Eriochrome Black T for total hardness (Ca 2+ + Mg 2+), where Mg 2+ is obtained by difference (Raij, 1966; Embrapa, 1997; Cantarella et al., 2001; Embrapa, 2005). Procedure for calculation of hardness of water by EDTA titration. 3 22. PAGE \* MERGEFORMAT 1 U U U U U U U U U. (not!all!of . 0.2 x X3 xY / 1 x 0.1 = Z mg of calcium. EBAS - equation balancer & stoichiometry calculator, Operating systems: XP, Vista, 7, 8, 10, 11, BPP Marcin Borkowskiul. Your TA will give you further information on how you will obtain your data. Figure 9.29b shows the pCd after adding 5.00 mL and 10.0 mL of EDTA. 0000034266 00000 n 0000020364 00000 n In this method buffer solution is used for attain suitable condition i.e pH level above 9 for the titration. To indicate the equivalence points volume, we draw a vertical line corresponding to 25.0 mL of EDTA. The blue line shows the complete titration curve. The equivalence point of a complexation titration occurs when we react stoichiometrically equivalent amounts of titrand and titrant. Hardness is mainly the combined constituent of both magnesium and calcium. where VEDTA and VCu are, respectively, the volumes of EDTA and Cu. 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, \[\textrm{Cd}^{2+}(aq)+\textrm Y^{4-}(aq)\rightarrow \textrm{CdY}^{2-}(aq)\]. 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 . Perform calculations to determine the concentration of calcium and magnesium ions in the hard water. A blank solution (distilled water) was also titrated to be sure that calculations were correct. A pH indicatorxylene cyanol FFis added to ensure that the pH is within the desired range. Just like during determination of magnesium all metals other than alkali metals can interfere and should be removed prior to titration. (mg) =Volume. The alpha fraction for Y4-is 0.355 at a pH of 10.0. Step 3: Calculate pM values before the equivalence point by determining the concentration of unreacted metal ions. Figure 9.28 Titration curve for the titration of 50.0 mL of 5.00103 M Cd2+ with 0.0100 M EDTA at a pH of 10 and in the presence of 0.0100 M NH3. 5. Finally, a third 50.00-mL aliquot was treated with 50.00 mL of 0.05831 M EDTA, and back titrated to the murexide end point with 6.21 mL of 0.06316 M Cu2+. trailer Repeat the titration twice. The end point is the color change from red to blue. Transfer magnesium solution to Erlenmeyer flask. The point in a titration when the titrant and analyte are present in stoichiometric amounts is called the equivalence point. trailer A more recent method is the titration of magnesium solution with ethylene-diamine tetra-acetate(Carr and Frank, 1956). a mineral analysis is performed, hardness by calculation can be reported. 0000005100 00000 n hbbe`b``3i~0 Finally, we complete our sketch by drawing a smooth curve that connects the three straight-line segments (Figure 9.29e). Figure 9.34 Titration curves illustrating how we can use the titrands pH to control EDTAs selectivity. The red arrows indicate the end points for each titration curve. and pCd is 9.77 at the equivalence point. Report the purity of the sample as %w/w NaCN. Complexometric titration is used for the estimation of the amount of total hardness in water. EDTA can form four or six coordination bonds with a metal ion. EDTA (mol / L) 1 mol Calcium. It is widely used in the pharmaceutical industry to determine the metal concentration in drugs. Step 1: Calculate the conditional formation constant for the metalEDTA complex. The analogous result for a complexation titration shows the change in pM, where M is the metal ion, as a function of the volume of EDTA. We can solve for the equilibrium concentration of CCd using Kf and then calculate [Cd2+] using Cd2+. The availability of a ligand that gives a single, easily identified end point made complexation titrimetry a practical analytical method. In this case the interference is the possible precipitation of CaCO3 at a pH of 10. Before adding EDTA, the mass balance on Cd2+, CCd, is, and the fraction of uncomplexed Cd2+, Cd2+, is, \[\alpha_{\textrm{Cd}^{2+}}=\dfrac{[\mathrm{Cd^{2+}}]}{C_\textrm{Cd}}\tag{9.13}\]. Beginning with the conditional formation constant, \[K_\textrm f'=\dfrac{[\mathrm{CdY^{2-}}]}{[\mathrm{Cd^{2+}}]C_\textrm{EDTA}}=\alpha_\mathrm{Y^{4-}} \times K_\textrm f = (0.37)(2.9\times10^{16})=1.1\times10^{16}\], we take the log of each side and rearrange, arriving at, \[\log K_\textrm f'=-\log[\mathrm{Cd^{2+}}]+\log\dfrac{[\mathrm{CdY^{2-}}]}{C_\textrm{EDTA}}\], \[\textrm{pCd}=\log K_\textrm f'+\log\dfrac{C_\textrm{EDTA}}{[\mathrm{CdY^{2-}}]}\]. The mean corrected titration volume of the EDTA solution was 16.25 mL (0.01625 L). 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. &=\dfrac{(5.00\times10^{-3}\textrm{ M})(\textrm{50.0 mL})}{\textrm{50.0 mL + 25.0 mL}}=3.33\times10^{-3}\textrm{ M} EDTA Titration You would like to perform a titration of 50.00 mL of a 1.00 x 10-4 M Zn2+ solution with a 1.00 x 10-4 M EDTA solution. The most likely problem is spotting the end point, which is not always sharp. Reaction taking place during titration is. +h;- h% 5CJ OJ QJ ^J aJ mHsHhs CJ OJ QJ ^J aJ h, CJ OJ QJ ^J aJ #hs h% CJ H*OJ QJ ^J aJ h, h% CJ OJ QJ ^J aJ h, h% CJ OJ QJ ^J aJ hk h% CJ OJ QJ ^J aJ &h, h% 5CJ H*OJ QJ ^J aJ &h, h% 5CJ H*OJ QJ ^J aJ #h, h% 5CJ OJ QJ ^J aJ h, 5CJ OJ QJ ^J aJ v x F  n o d 7$ 8$ H$ ^`gd Detection is done using a conductivity detector. This is often a problem when analyzing clinical samples, such as blood, or environmental samples, such as natural waters. Take a sample volume of 20ml (V ml). Calculate the number of grams of pure calcium carbonate required to prepare a 100.0 mL standard calcium solution that would require ~35 mL of 0.01 M EDTA for titration of a 10.00 mL aliquot: g CaCO 3 = M EDTA x 0.035L x 1 mol CaCO 3/1 mol EDTA x MM CaCO 3 x 100.0mL/10.00mL 3. of which 1.524103 mol are used to titrate Ni. [\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}}\\ First, we add a ladder diagram for the CdY2 complex, including its buffer range, using its logKf value of 16.04. h% CJ OJ QJ ^J aJ h`. Of the cations contributing to hardness, Mg2+ forms the weakest complex with EDTA and is the last cation to be titrated. 0000001156 00000 n a pCd of 15.32. The indicators end point with Mg2+ is distinct, but its change in color when titrating Ca2+ does not provide a good end point. It can be determined using complexometric titration with the complexing agent EDTA. ), The primary standard of Ca2+ has a concentration of, \[\dfrac{0.4071\textrm{ g CaCO}_3}{\textrm{0.5000 L}}\times\dfrac{\textrm{1 mol Ca}^{2+}}{100.09\textrm{ g CaCO}_3}=8.135\times10^{-3}\textrm{ M Ca}^{2+}\], \[8.135\times10^{-3}\textrm{ M Ca}^{2+}\times0.05000\textrm{ L Ca}^{2+} = 4.068\times10^{-4}\textrm{ mol Ca}^{2+}\], which means that 4.068104 moles of EDTA are used in the titration. Figure 9.30 is essentially a two-variable ladder diagram. Step 4: Calculate pM at the equivalence point using the conditional formation constant. Note that the titration curves y-axis is not the actual absorbance, A, but a corrected absorbance, Acorr, \[A_\textrm{corr}=A\times\dfrac{V_\textrm{EDTA}+V_\textrm{Cu}}{V_\textrm{Cu}}\]. For example, calmagite gives poor end points when titrating Ca2+ with EDTA. Calcium. 3: Hardness (in mg/L as CaCO 3 . Next, we solve for the concentration of Cd2+ in equilibrium with CdY2. 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. lab report 6 determination of water hardnessdream about someone faking their death. Eriochrome Black-T(EBT) is the metal ion indicator used in the determination of hardness by complexometric titration with EDTA. Figure 9.30 (a) Predominance diagram for the metallochromic indicator calmagite showing the most important form and color of calmagite as a function of pH and pMg, where H2In, HIn2, and In3 are uncomplexed forms of calmagite, and MgIn is its complex with Mg2+. 0000022889 00000 n ! Add 1 or 2 drops of the indicator solution. h, CJ H*OJ QJ ^J aJ mHsH(h Reporting Results A 0.7176-g sample of the alloy was dissolved in HNO3 and diluted to 250 mL in a volumetric flask. In addition, EDTA must compete with NH3 for the Cd2+. At the equivalence point we know that, \[M_\textrm{EDTA}\times V_\textrm{EDTA}=M_\textrm{Cd}\times V_\textrm{Cd}\], Substituting in known values, we find that it requires, \[V_\textrm{eq}=V_\textrm{EDTA}=\dfrac{M_\textrm{Cd}V_\textrm{Cd}}{M_\textrm{EDTA}}=\dfrac{(5.00\times10^{-3}\;\textrm M)(\textrm{50.0 mL})}{\textrm{0.0100 M}}=\textrm{25.0 mL}\]. 0000001334 00000 n The fully protonated form of EDTA, H6Y2+, is a hexaprotic weak acid with successive pKa values of. Indicator. MgSO4 Mg2++SO42- Experimental: B. Step 2: Calculate the volume of EDTA needed to reach the equivalence point. Click Use button. (Use the symbol Na 2 H 2 Y for Na 2 EDTA.) 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. EDTA forms a chelation compound with magnesium at alkaline pH. We also will learn how to quickly sketch a good approximation of any complexation titration curve using a limited number of simple calculations. Other common spectrophotometric titration curves are shown in Figures 9.31b-f. Although each method is unique, the following description of the determination of the hardness of water provides an instructive example of a typical procedure. For a titration using EDTA, the stoichiometry is always 1:1. (b) Titration of a 50.0 mL mixture of 0.010 M Ca2+ and 0.010 M Ni2+ at a pH of 3 and a pH of 9 using 0.010 M EDTA. Now that we know something about EDTAs chemical properties, we are ready to evaluate its usefulness as a titrant. The reaction between Cl and Hg2+ produces a metalligand complex of HgCl2(aq). By direct titration, 5 ml. Truman State University CHEM 222 Lab Manual Revised 01/04/08 REAGENTS AND APPARATUS the solutions used in here are diluted. When the titration is complete, raising the pH to 9 allows for the titration of Ca2+. Figure 9.26 Structures of (a) EDTA, in its fully deprotonated form, and (b) in a six-coordinate metalEDTA complex with a divalent metal ion. The sample is acidified to a pH of 2.33.8 and diphenylcarbazone, which forms a colored complex with excess Hg2+, serves as the indicator. Table 9.10 provides values of Y4 for selected pH levels. ! EDTA Titration for Determination of calcium and magnesium - In this procedure a stock solution of - Studocu chemistry 321: quantitative analysis lab webnote edta titration for determination of calcium and magnesium before attempting this experiment, you may need to Skip to document Ask an Expert Sign inRegister Sign inRegister Home Ask an ExpertNew At a pH of 3 the CaY2 complex is too weak to successfully titrate. The value of Cd2+ depends on the concentration of NH3. Add a pinch of Eriochrome BlackT ground with sodium chloride (100mg of indicator plus 20g of analytical grade NaCl). The resulting metalligand complex, in which EDTA forms a cage-like structure around the metal ion (Figure 9.26b), is very stable.